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1.
  • Abbas, Ghulam, et al. (författare)
  • Quasi Three-Dimensional Tetragonal SiC Polymorphs as Efficient Anodes for Sodium-Ion Batteries
  • 2023
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:17, s. 8976-8988
  • Tidskriftsartikel (refereegranskat)abstract
    • In the present work, we investigate, for the first time, quasi 3D porous tetragonal silicon–carbon polymorphs t(SiC)12 and t(SiC)20 on the basis of first-principles density functional theory calculations. The structural design of these q3-t(SiC)12 and q3-t(SiC)20 polymorphs follows an intuitive rational approach based on armchair nanotubes of a tetragonal SiC monolayer where C–C and Si–Si bonds are arranged in a paired configuration for retaining a 1:1 ratio of the two elements. Our calculations uncover that q3-t(SiC)12 and q3-t(SiC)20 polymorphs are thermally, dynamically, and mechanically stable with this lattice framework. The results demonstrate that the smaller polymorph q3-t(SiC)12 shows a small band gap (∼0.59 eV), while the larger polymorph of q3-t(SiC)20 displays a Dirac nodal line semimetal. Moreover, the 1D channels are favorable for accommodating Na ions with excellent (>300 mAh g–1) reversible theoretical capacities. Thus confirming potential suitability of the two porous polymorphs with an appropriate average voltage and vanishingly small volume change (<6%) as anodes for Na-ion batteries.
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2.
  • Afroz, Laila, et al. (författare)
  • Nanocomposite Catalyst (1 – x)NiO-xCuO/yGDC for Biogas Fueled Solid Oxide Fuel Cells
  • 2023
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:21, s. 10918-10928
  • Tidskriftsartikel (refereegranskat)abstract
    • The composites of Ni–Cu oxides with gadolinium doped ceria (GDC) are emerging as highly proficient anode catalysts, owing to their remarkable performance for solid oxide fuel cells operated with biogas. In this context, the nanocomposite catalysts (1 – x)NiO-xCuO/yGDC (x = 0.2–0.8; y = 1,1.3) are synthesized using a solid-state reaction route. The cubic and monoclinic structures are observed for NiO and CuO phases, respectively, while CeO2 showed cubic fluorite structure. The scanning electron microscopic images revealed a rise in the particle size with an increase in the copper and GDC concentration. The optical band gap values are calculated in the range 2.82–2.33 eV from UV–visible analysis. The Raman spectra confirmed the presence of vibration modes of CeO2 and NiO. The electrical conductivity of the nanocomposite anodes is increased as the concentration of copper and GDC increased and reached at 9.48 S cm–1 for 0.2NiO-0.8CuO/1.3GDC composition at 650 °C. The electrochemical performance of (1 – x)NiO-xCuO/yGDC (x = 0.2–0.8; y = 1,1.3)-based fuel cells is investigated with biogas fuel at 650 °C. Among all of the as-synthesized anodes, the fuel cell with composition 0.2NiO-0.8CuO/1.3GDC showed the best performance, such as an open circuit voltage of 0.84 V and peak power density of 72 mW cm–2. However, from these findings, it can be inferred that among all other compositions, the 0.2NiO-0.8CuO/1.3GDC anode is a superior combination for the high electrochemical performance of solid oxide fuel cells fueled with biogas.
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3.
  • Ahmad, Shargeel, et al. (författare)
  • Photon Up-Conversion via Epitaxial Surface-Supported Metal-Organic Framework Thin Films with Enhanced Photocurrent
  • 2018
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:2, s. 249-253
  • Tidskriftsartikel (refereegranskat)abstract
    • We report a new triplet-triplet annihilation photon up-conversion (TTA-UC) system using an epitaxial Zn-perylene surface-supported metal-organic framework (SURMOF) grown on metal oxide surface as "emitter", and a platinum octaethylporphyrin (PtOEP) as "sensitizer" in [Co(bpy)(3)](2+/3+) acetonitrile solution. It has been demonstrated that the photocurrent can be significantly enhanced relative to epitaxial Zn-perylene SURMOF due to the TTA-UC mechanism. This initial result holds promising applications toward SURMOF-based solar energy conversion devices.
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4.
  • Aktekin, Burak, et al. (författare)
  • Cation Ordering and Oxygen Release in LiNi0.5-xMn1.5+xO4-y (LNMO) : In Situ Neutron Diffraction and Performance in Li Ion Full Cells
  • 2019
  • Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 2:5, s. 3323-3335
  • Tidskriftsartikel (refereegranskat)abstract
    • Lithium ion cells utilizing LiNi0.5Mn1.5O4 (LNMO) as the positive electrode are prone to fast capacity fading, especially when operated in full cells and at elevated temperatures. The crystal structure of LNMO can adopt a P4(3)32 (cation-ordered) or Fd (3) over barm (disordered) arrangement, and the fading rate of cells is usually mitigated when samples possess the latter structure. However, synthesis conditions leading to disordering also lead to oxygen deficiencies and rock-salt impurities and as a result generate Mn3+. In this study, in situ neutron diffraction was performed on disordered and slightly Mn-rich LNMO samples to follow cation ordering-disordering transformations during heating and cooling. The study shows for the first time that there is not a direct connection between oxygen release and cation disordering, as cation disordering is observed to start prior to oxygen release when the samples are heated in a pure oxygen atmosphere. This result demonstrates that it is possible to tune disordering in LNMO without inducing oxygen deficiencies or forming the rock-salt impurity phase. In the second part of the study, electrochemical testing of samples with different degrees of ordering and oxygen content has been performed in LNMO vertical bar vertical bar LTO (Li4Ti5O12) full cells. The disordered sample exhibits better performance, as has been reported in other studies; however, we observe that all cells behave similarly during the initial period of cycling even when discharged at a 10 C rate, while differences arise only after a period of cycling. Additionally, the differences in fading rate were observed to be time-dependent rather than dependent on the number of cycles. This performance degradation is believed to be related to instabilities in LNMO at higher voltages, that is, in its lower lithiation states. Therefore, it is suggested that future studies should target the individual effects of ordering and oxygen content. It is also suggested that more emphasis during electrochemical testing should be placed on the stability of samples in their delithiated state.
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5.
  • Aktekin, Burak, et al. (författare)
  • Concentrated LiFSI-€“Ethylene Carbonate Electrolytes and Their Compatibility with High-Capacity and High-Voltage Electrodes
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:1, s. 585-595
  • Tidskriftsartikel (refereegranskat)abstract
    • The unusual physical and chemical properties of electrolytes with excessive salt contents have resulted in rising interest in highly concentrated electrolytes, especially for their application in batteries. Here, we report strikingly good electrochemical performance in terms of conductivity and stability for a binary electrolyte system, consisting of lithium bis(fluorosulfonyl)imide (LiFSI) salt and ethylene carbonate (EC) solvent. The electrolyte is explored for different cell configurations spanning both high-capacity and high-voltage electrodes, which are well known for incompatibilities with conventional electrolyte systems: Li metal, Si/graphite composites, LiNi0.33Mn0.33Co0.33O2 (NMC111), and LiNi0.5Mn1.5O4 (LNMO). As compared to a LiTFSI counterpart as well as a common LP40 electrolyte, it is seen that the LiFSI:EC electrolyte system is superior in Li-metal–Si/graphite cells. Moreover, in the absence of Li metal, it is possible to use highly concentrated electrolytes (e.g., 1:2 salt:solvent molar ratio), and a considerable improvement on the electrochemical performance of NMC111-Si/graphite cells was achieved with the LiFSI:EC 1:2 electrolyte both at the room temperature and elevated temperature (55 °C). Surface characterization with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) showed the presence of thicker surface film formation with the LiFSI-based electrolyte as compared to the reference electrolyte (LP40) for both positive and negative electrodes, indicating better passivation ability of such surface films during extended cycling. Despite displaying good stability with the NMC111 positive electrode, the LiFSI-based electrolyte showed less compatibility with the high-voltage spinel LNMO electrode (4.7 V vs Li+/Li).
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6.
  • Aktekin, Burak, et al. (författare)
  • How Mn/Ni Ordering Controls Electrochemical Performance in High-Voltage Spinel LiNi0.44Mn1.56O4 with Fixed Oxygen Content
  • 2020
  • Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:6, s. 6001-6013
  • Tidskriftsartikel (refereegranskat)abstract
    • The crystal structure of LiNi0.5O4 (LNMO) can adopt either low-symmetry ordered (Fd (3) over barm) or high-symmetry disordered (P4(3)32) space group depending on the synthesis conditions. A majority of published studies agree on superior electrochemical performance of disordered LNMO, but the underlying reasons for improvement remain unclear due to the fact that different thermal history of the samples affects other material properties such as oxygen content and particle morphology. In this study, ordered and disordered samples were prepared with a new strategy that renders samples with identical properties apart from their cation ordering degree. This was achieved by heat treatment of powders under pure oxygen atmosphere at high temperature with a final annealing step at 710 degrees C for both samples, followed by slow or fast cooling. Electrochemical testing showed that cation disordering improves the stability of material in charged (delithiated) state and mitigates the impedance rise in LNMO parallel to LTO (Li4Ti5O12) and LNMO parallel to Li cells. Through X-ray photoelectron spectroscopy (XPS), thicker surface films were observed on the ordered material, indicating more electrolyte side reactions. The ordered samples also showed significant changes in the Ni 2p XPS spectra, while the generation of ligand (oxygen) holes was observed in the Ni-O environment for both samples using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). Moreover, high-resolution transmission electron microscopy (HRTEM) images indicated that the ordered samples show a decrease in ordering near the particle surface after cycling and a tendency toward rock-salt-like phase transformations. These results show that the structural arrangement of Mn/Ni (alone) has an effect on the surface and "nearsurface" properties of LNMO, particularly in delithiated state, which is likely connected to the bulk electronic properties of this electrode material.
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7.
  • Ali, Amjad, et al. (författare)
  • Effect of Manganese Catalysts on the Performance of Anodes in Direct Carbon Fuel Cells
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 5:6, s. 6878-6885
  • Tidskriftsartikel (refereegranskat)abstract
    • The efficiency of direct carbon fuel cells is higher than that of solid oxide fuel cells. The direct carbon fuel cell transforms chemical energy into electrical energy. In this work, the La0.4Sr0.6MnxTi1-xO3-delta (x = 0.02, 0.04, 0.06, 0.08) anode material has been synthesized by the combustion method to examine the device performance. X-ray analysis confirmed the single-perovskite cubic structure with an average crystalline size of 80 nm. An electrical conductivity of 2.1 S cm-1 and fuel cell performance of 100 mW cm-2 at 600 degrees C are measured with sub-bituminous fuel. Theoretical results describe the minor contribution of manganese (Mn) in the valence band and the major one in the conduction band, and with minimum energy, the Mn electrons may jump in the conduction band. Moreover, density functional theory confirmed that with an increase in the Mn concentration, Mn and Ti energy states appear at the Fermi level, which reveals that the conductivity of the compound has improved, agreeing with the experimental results that the Mn concentration led to the enhancement of the conductivity.
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8.
  • Ali, Amjad, et al. (författare)
  • Electrochemical Analysis of a Titanate-Based Anode for Direct Carbon Fuel Cells
  • 2020
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:9, s. 9182-9189
  • Tidskriftsartikel (refereegranskat)abstract
    • The grand challenge in the commercialization of direct carbon fuel cell (DCFC) technology is the development of a cost-effective and thermally stable material, which facilitates fast ionic and electronic conduction and exhibits good resistance for carbon deposition at electrodes. Titanate-based materials have high ionic and electronic conductivity at higher temperature. Perovskite anodes based on titanate and transition metals show a good catalytic activity for hydrocarbon fuels. Therefore, perovskite materials, based on lanthanum strontium and copper titanate La0.4Sr0.6CuxTi1-3O3-delta (x = 0.02, 0.04, 0.06, and 0.08), were synthesized using the sol-gel method and examined as anodes for DCFCs. The powders were analyzed using various characterization techniques. X-ray diffraction shows that the material has a cubic perovskite structure. The conductivity of the synthesized powder LS8CT was found to be 4.21 Scm(-1) at 600 degrees C. The button cell developed using LS8CT exhibits a performance of 61mWcm 72. at 600 degrees C. The computational study using the Wien2k code has been performed, which shows that the Fermi level is at nonzero density of states (DOS) and reveals that the compound is metallic in nature. Therefore, no forbidden region occurs between the maxima of the valence band and minima of the conduction band. Results of DOS confirm the metallic nature of the compound. On the basis of theoretical and experimental studies, it can be depicted that substitution of Cu in La0.3Sr0.7TiO3 increases the conductivity. Therefore, a La0.4Sr0.6CuxTi1-xO3-delta perovskite material can be used as an anode for DCFCs.
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9.
  • Alkadir Abdulahi, Birhan, 1985, et al. (författare)
  • Open-Circuit Voltage Modulations on All-Polymer Solar Cells by Side Chain Engineering on 4,8-Di(thiophen-2-yl)benzo[1,2- b:4,5- b′]dithiophene-Based Donor Polymers
  • 2018
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:6, s. 2918-2926
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years, all-polymer solar cells (all-PSCs), incorporating active layers based on blends of electron-donor (D) and acceptor (A) polymers, have drawn attention because of the advantages they hold in the flexibility of choosing the D:A combinations to modulate their energy levels and to improve their overall open-circuit voltages (V oc ) and power conversion efficiencies (PCE)s. V oc is one of the key parameters for the determination of the PCEs of PSCs. In this work, we synthesized six donor polymers with three different side chains appended to the 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene (BDT) units. By substituting carbon with sulfur and silicon atoms at the 5-position of the thiophenes attached to the BDT units, the highest occupied molecular orbital (HOMO) levels of the donor polymers could be successfully lowered. As anticipated, the V oc values of the resulting all-PSCs increased along with the lowering of the HOMO levels of the donor polymers. Among the six all-PSCs, the PBDT-BDD:PNDI-T10 all-PSC realized a balance between the photovoltage and photocurrent, where a decent PCE of 5.6% was obtained with a V oc of 0.9 V and a photocurrent of 10.5 mA/cm 2 .
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10.
  • Andersson, Rassmus, et al. (författare)
  • Designing Polyurethane Solid Polymer Electrolytes for High-Temperature Lithium Metal Batteries
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:1, s. 407-418
  • Tidskriftsartikel (refereegranskat)abstract
    • Potentially high-performance lithium metal cells in extreme high-temperature electrochemical environments is a challenging but attractive battery concept that requires stable and robust electrolytes to avoid severely limiting lifetimes of the cells. Here, the properties of tailored polyester and polycarbonate diols as the soft segments in polyurethanes are investigated and electrochemically evaluated for use as solid polymer electrolytes in lithium metal batteries. The polyurethanes demonstrate high mechanical stability against deformation at low flow rates and moreover at temperatures up above 100 degrees C, enabled by the hard urethane segments. The results further indicate transferrable ion transport properties of the pure polymers when incorporated as the soft segments in the polyurethanes, offering designing opportunities of the polyurethane by tuning the soft segment ratio and composition. Long-term electrochemical cycling of polyurethane-containing cells in lithium metal batteries at 80 degrees C proves the stability at elevated temperatures as well as the compatibility with lithium metal with stable cycling maintained after 2000 cycles.
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11.
  • Aryal, Um Kanta, et al. (författare)
  • 2D MXene-Based Electron Transport Layers for Nonhalogenated Solvent-Processed Stable Organic Solar Cells
  • 2023
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:9, s. 4549-4558
  • Tidskriftsartikel (refereegranskat)abstract
    • Implementation of 2D materials is one of the promising routes for improving the efficiency and stability of organic solar cells (OSCs). Due to their tunable optical and electronic properties, MXenes, a family of 2D transition metal carbides and nitrides, have attracted considerable attention and demonstrated their potential for next-generation solar cells. In this work, Ti3C2Tx MXene was added into ZnO precursors and applied as a modified composite electron transport layer (ETL) in PM6:N3-based inverted OSCs. The nonhalogenated solvent o-xylene was employed as the active layer solvent for the development of stable, efficient, and eco-friendly OSCs. By optimizing the concentration of Ti3C2Tx in the ZnO ETL, the solar cells exhibited power conversion efficiencies (PCEs) of 14.1 and 13.7% for 0.5 and 2 wt % MXene, respectively, as compared to neat ZnO layer devices with a PCE of 14.9%. Interestingly, the MXene-based PM6:N3 OSC devices showed superior device stability compared to the reference cells. It is demonstrated that the MXene introduced in the composite ZnO-based ETL mitigates the photocatalytic decomposition of the organic active layer on the ZnO surface, as analyzed via optical spectroscopy and hard X-ray photoelectron spectroscopy, which appears as a main reason for improved device stability. We thus report on the usage of MXene in green solvent-processed OSCs to enhance the lifetime of solar cells and thus address an important bottleneck in high-performance nonfullerene acceptor solar cells.
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12.
  • Ayaz, Muhammad, et al. (författare)
  • Improved Dye Regeneration through Addition of a Triphenylamine Electron Donor in Iodide-Based Electrolytes for Dye-Sensitized Solar Cells
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:4, s. 4240-4246
  • Tidskriftsartikel (refereegranskat)abstract
    • The addition of a small organic electron donor, tris(p-anisyl)amine (TPAA), to an iodide/triiodide electrolyte for dye-sensitized solar cells was found to give pronounced effects on charge transfer reactions. When using the organic dye LEG4 as a sensitizer, an improved solar cell performance was found, which could be attributed to the extremely rapid dye regeneration reaction when TPAA is added. In contrast, for the ruthenium dye N719, no significant solar cell improvement was found, despite rapid dye regeneration. Using transient absorption measurements, it was found that reduction of the intermediate TPAA(+) by iodide is sluggish. This allows for significant recombination of electrons in TiO2 to TPAA(+) when the adsorbed dye layer does not have sufficient electron-blocking properties.
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13.
  • Babucci, Melike, et al. (författare)
  • Depth-Dependent Atomic-Scale Structural Changes in (Ag,Cu)(In,Ga)Se2 Absorbers Relevant for Thin-Film Solar Cells
  • 2023
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:18, s. 9264-9275
  • Tidskriftsartikel (refereegranskat)abstract
    • Alloying a Cu(In,Ga)Se-2 (CIGS) solar cell absorber with silver to form (Ag,Cu)(In,Ga)Se-2 (ACIGS) is an effective route for improving the performance of CIGS-based thin-film solar cells by increasing the optical band gap and open-circuit voltage. While the role of Ag on the solar cell's performance and crystal structure has been analyzed, important gaps in our understanding remain, especially regarding the atomistic (short-range) structure. Previous X-ray absorption spectroscopy (XAS) results have shown that local atomic arrangements in Ag-free CIGS deviate from the long-range crystallographic structure deduced from X-ray diffraction (XRD). However, it is unclear how these structural deviations evolve with Ag alloying, particularly in the presence of Ga depth gradient. In this work, we employ angle-resolved XAS to probe the local environment of Se atoms within different depths of ACIGS absorbers with varying Ag content and Ga depth gradient. By complementing XAS results with X-ray diffraction measurements for long-range structures, glow discharge optical emission spectroscopy for elemental profiles, and scanning transmission electron microscopy for morphologies, changes in element-specific bond lengths, cell parameters, and anion displacement depending on compositions of Group [I] (Cu, Ag) and Group [III] (In, Ga) elements were mapped. The results suggest that the local atomic arrangement of the investigated ACIGS thin-film solar cell samples is depth-dependent and deviates from the long-range crystallographic structure. Possible reasons include tetragonal distortion or the presence of other phases or off-stoichiometry compounds. For the sample with the highest Ag content, increased bond lengths of Se-Group [I] atoms and Se-Ga are observed from the absorber bulk toward the near-absorber/buffer interface, whereas, in Ag-free CIGS, no significant changes are found. Results further indicate nonlinear anion displacement with Ag addition in the absorber bulk or with depth composition variation, which is likely to affect the electronic properties of solar cells. These findings offer a better understanding of the atomic-scale properties of ACIGS absorbers in actual thin-film solar cells containing in-depth composition variations.
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14.
  • Banerjee, Amitava, et al. (författare)
  • Rashba Triggered Electronic and Optical Properties Tuning in Mixed Cation-Mixed Halide Hybrid Perovskites
  • 2019
  • Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 2:10, s. 6990-6997
  • Tidskriftsartikel (refereegranskat)abstract
    • The inherent spin-orbit coupling (SOC) effect in non-centrosymmetric crystal structure has laid the foundation of Rashba splitting phenomena. This Rashba splitting directly governs the charge carrier recombination, which eventually controls the carrier lifetime and diffusion length and therefore the solar cell efficiency for such hybrid perovskite materials. In this work, we have performed a rigorous structural search prediction of the mixed cation-mixed halide hybrid perovskites FA(0.83)MA(0.17)Pb(I0.83Br0.17)(3) and FA(0.875)MA(0.125 )Pb(I0.875Br (0.125))(3), which are the two nearest neighbor structures of record efficiency (22.1%) holder FA(0.85)MA(0.15)Pb(I0.85Br0.15)(3) in the structural composition phase space. We have found the prediction routes for a structural search such as the mixed perovskite structure govern the Rashba splitting energy value, depending on whether it has been predicted from FPI (FAPbI(3)) or MPB (MAPbBr(3)) as parent structure, which are leading to the mixed phase FA(0.83)MA(0.17)Pb(I0.83Br0.17)(3) and FA(0.875)MA(0.125)Pb(I0.875Br0.125)(3) respectively. The strong dependency of the splitting energy on the structural phase evolution along with the stoichiometry and space group is also observed, where in the mixed phase, 0.045 difference in concentration could lead to a remarkable difference in the splitting energy, which is more pronounced in the valence band as compared to the conduction band. We have also determined the Goldschmidt tolerance factor to envisage structural stability of the newly predicted crystal structures based on the corresponding chemical route in the composition phase space.
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15.
  • Banerjee, Amitava, et al. (författare)
  • Scrupulous Probing of Bifunctional Catalytic Activity of Borophene Monolayer : Mapping Reaction Coordinate with Charge Transfer
  • 2018
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:8, s. 3571-3576
  • Tidskriftsartikel (refereegranskat)abstract
    • We have envisaged the hydrogen evolution and oxygen evolution reactions (HER and OER) on two-dimensional (2D) noble metal free borophene monolayer based on first-principles electronic structure calculations. We have investigated the effect of Ti functionalization on borophene monolayer from the perspective of HER and OER activities enhancement. We have probed the activities based on the reaction coordinate, which is conceptually related to the adsorption free energies of the intermediates of HER and OER, as well as from the vibrational frequency analysis with the corresponding charge transfer mechanism between the surface and the adsorbate. Tifunctionalized borophene has emerged as a promising material for HER and OER mechanisms. We believe that our probing method, based on reaction coordinate coupled with vibrational analysis that has been validated by the charge transfer mechanism, would certainly become as a robust prediction route for HER and OER mechanisms in coming days.
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16.
  • Barthwal, M., et al. (författare)
  • Effect of Nanomaterial Inclusion in Phase Change Materials for Improving the Thermal Performance of Heat Storage : A Review
  • 2021
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:8, s. 7462-7480
  • Tidskriftsartikel (refereegranskat)abstract
    • Dispersion of nanoparticles is one of the potential solutions to improve the thermophysical properties of phase change (or transition) materials (PCMs) and enhance the performance of latent thermal energy storage (LTES) systems. The PCM ought to have a high latent heat of fusion, and zero or negligible coefficient of thermal expansion. A good PCM should have melting and solidification compatibility with negligible or zero subcooling, and it should not react with the common chemical reagents. The present known PCMs possess low thermal conductivity that results into a longer solidification and melting time of PCMs. In the past two decades, researchers have reported improved thermal conductivity and heat-storing capacity of PCMs employing graphite nanoparticles/fibers, carbon nanotubes/fibers, metal, and metal oxide nanoparticles. This work reviews the reported experimental and numerical studies describing the consequences of nanoparticle inclusions of various shapes and sizes on the thermal properties of the PCMs. This review attempts to make a consolidated database of the studies related to nanoadditive inclusion into PCMs for various applications. Graphene dispersed into PCM has resulted into 14 times thermal conductivity enhancement. As far as metal oxide nanoparticles are concerned, TiO2 and Al2O3 nanoparticles outperformed others. The compatibility between the nanoadditive and PCM is necessary to tailor favorable thermal properties. This work reviews numerous studies of different nanoparticle-PCM duos. © 2021 American Chemical Society.
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17.
  • Bini, Kim, 1987, et al. (författare)
  • Alcohol-Soluble Conjugated Polymers as Cathode Interlayers for All-Polymer Solar Cells
  • 2018
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:5, s. 2176-2182
  • Tidskriftsartikel (refereegranskat)abstract
    • Conjugated polymers with polar side-chain components have successfully been used as cathode interfacial materials (CIMs) to improve the performances of polymer solar cells with fullerenes as acceptors. However, their uses and functions in all-polymer solar cells (all-PSCs) have not been well-investigated. Therefore, in this work, four conjugated polymers bearing different functional side chains, including dimethylamine, diethanolamine, and imidazole, were used as CIMs to study their effects on all-PSCs. With a combination of high-performing acceptor and donor polymers as active layers, the performances of the devices based on the four CIMs were compared with conventional devices with LiF/Al and Al as cathode. Compared to the devices with only Al as cathode, the devices comprising conjugated polymers as CIMs presented large improvement in power conversion efficiency from 2.7% to around 5.3%, which is comparable to the devices with LiF/Al as cathode. The encouraging results demonstrated that the use of conjugated interfacial polymers is a robust way to improve the performances of all-PSCs and can elegantly circumvent the use of low work function metals as cathodes. This is very important for roll-to-roll processing of flexible and large-scale solar cells.
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18.
  • Bunea, Ada-Ioana, et al. (författare)
  • Micropatterned Carbon-on-Quartz Electrode Chips for Photocurrent Generation from Thylakoid Membranes
  • 2018
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:7, s. 3313-3322
  • Tidskriftsartikel (refereegranskat)abstract
    • Harvesting the energy generated by photosynthetic organisms through light-dependent reactions is a significant step toward a sustainable future energy supply. Thylakoid membranes are the site of photosynthesis, and thus particularly suited for developing photo-bioelectrochemical cells. Novel electrode materials and geometries could potentially improve the efficiency of energy harvesting using thylakoid membranes. For commercial applications, electrodes with large surface areas are needed. Photolithographic patterning of a photoresist, followed by pyrolysis, is a flexible and fast approach for the fabrication of carbon electrodes with tailored properties. In this work, electrode chips consisting of patterned carbon supported on quartz were designed and fabricated. The patterned electrode area is 1 cm2, and the measurement chamber footprint is 0.5 cm2, 1 order of magnitude larger than previously tested electrodes for thylakoid membrane immobilization. The use of a transparent substrate allows back-side illumination, protecting the bioelectrochemical system from the environment and vice versa. Two different mediators, monomeric ([Ru(NH3)6]3+) and polymeric ([Os(2,2′-bipyridine)2-poly(N-vinylimidazole)10Cl]+/2+), are used for evaluating photocurrent generation from thylakoid membranes with different electrode geometries. Current densities up to 71 μA cm–2 are measured upon illumination through the transparent electrode chip with solar simulated irradiance (1000 W m–2).
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19.
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20.
  • Burcea, Razvan, et al. (författare)
  • Influence of Generated Defects by Ar Implantation on the Thermoelectric Properties of ScN
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:9, s. 11025-11033
  • Tidskriftsartikel (refereegranskat)abstract
    • Nowadays, making thermoelectric materials more efficient in energy conversion is still a challenge. In this work, to reduce the thermal conductivity and thus improve the overall thermoelectric performances, point and extended defects were generated in epitaxial 111-ScN thin films by implantation using argon ions. The films were investigated by structural, optical, electrical, and thermoelectric characterization methods. The results demonstrated that argon implantation leads to the formation of stable defects (up to 750 K operating temperature). These were identified as interstitial-type defect dusters and argon vacancy complexes. The insertion of these specific defects induces acceptor-type deep levels in the band gap, yielding a reduction in the free-carrier mobility. With a reduced electrical conductivity, the irradiated sample exhibited a higher Seebeck coefficient while maintaining the power factor of the film. The thermal conductivity is strongly reduced from 12 to 3 W.m(-1). K-1 at 300 K, showing the influence of defects in increasing phonon scattering. Subsequent high-temperature annealing at 1573 K leads to the progressive evolution of these defects: the initial dusters of interstitials evolved to the benefit of smaller dusters and the formation of bubbles. Thus, the number of free carriers, the resistivity, and the Seebeck coefficient are almost restored but the mobility of the carriers remains low and a 30% drop in thermal conductivity is still effective (k(total) similar to 8.5 Wm(-1).K-1). This study shows that control defect engineering with defects introduced by irradiation using noble gases in a thermoelectric coating can be an attractive method to enhance the figure of merit of thermoelectric materials.
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21.
  • Butorin, Sergei, et al. (författare)
  • Effect of Ag Doping on Electronic Structure of Cluster Compounds AgxMo9Se11 (x = 3.4, 3.9)
  • 2018
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:8, s. 4032-4039
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of AgxMo9Se11 as a potential material for thermoelectric applications was studied using high-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) and the resonant inelastic X-ray scattering (RIXS) technique. The experiments were supported by first-principle calculations using density functional theory (DFT). The analysis of obtained spectra indicate the presence of subvalent (less than 1+) Ag in AgxMo9Se11. The advanced HERFD-XAS measurements allowed us to resolve the contribution of the electronic states at the Fermi level of AgxMo9Se11 and to monitor its dependence on the x value. A comparison of the experimental data with the results of the DFT calculations suggests the importance of the Ag2-type sites with the shortest Ag–Se distance for affecting the properties of AgxMo9Se11.
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22.
  • Cavallo, Carmen, 1986, et al. (författare)
  • Effect of the Niobium Doping Concentration on the Charge Storage Mechanism of Mesoporous Anatase Beads as an Anode for High-Rate Li-Ion Batteries
  • 2021
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:1, s. 215-225
  • Tidskriftsartikel (refereegranskat)abstract
    • A promising strategy to improve the rate performance of Li-ion batteries is to enhance and facilitate the insertion of Li ions into nanostructured oxides like TiO2. In this work, we present a systematic study of pentavalent-doped anatase TiO2 materials for third-generation high-rate Li-ion batteries. Mesoporous niobium-doped anatase beads (Nb-doped TiO2) with different Nb5+ doping (n-type) concentrations (0.1, 1.0, and 10% at.) were synthesized via an improved template approach followed by hydrothermal treatment. The formation of intrinsic n-type defects and oxygen vacancies under RT conditions gives rise to a metallic-type conduction due to a shift of the Fermi energy level. The increase in the metallic character, confirmed by electrochemical impedance spectroscopy, enhances the performance of the anatase bead electrodes in terms of rate capability and provides higher capacities both at low and fast charging rates. The experimental data were supported by density functional theory (DFT) calculations showing how a different n-type doping can be correlated to the same electrochemical effect on the final device. The Nb-doped TiO2 electrode materials exhibit an improved cycling stability at all the doping concentrations by overcoming the capacity fade shown in the case of pure TiO2 beads. The 0.1% Nb-doped TiO2-based electrodes exhibit the highest reversible capacities of 180 mAh g-1 at 1C (330 mA g-1) after 500 cycles and 110 mAh g-1 at 10C (3300 mA g-1) after 1000 cycles. Our experimental and computational results highlight the possibility of using n-type doped TiO2 materials as anodes in high-rate Li-ion batteries.
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23.
  • Chai, Zhigang, et al. (författare)
  • Ni–Ag Nanostructure-Modified Graphitic Carbon Nitride for Enhanced Performance of Solar-Driven Hydrogen Production from Ethanol
  • 2020
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:10, s. 10131-10138
  • Tidskriftsartikel (refereegranskat)abstract
    • Solar-driven splitting of alcohol utilizing photocatalysts is a promising route to obtain H2 and fine chemicals. Ni nanoparticles have shown great potential for light-driven splitting of alcohol, and their size, exposed facets, and electronic properties play key roles in the performance of photocatalysts. Therefore, purposefully modifying Ni is of great importance. In this report, Ni–Ag nanostructures were fabricated in situ on graphitic carbon nitride by a sequential photodeposition method. The solar-driven hydrogen production from ethanol was dramatically enhanced on the Ni–Ag nanostructure-modified graphitic carbon nitride compared with pure Ni nanoparticle-modified graphitic carbon nitride. It was found that the beneficial role of Ag is to disperse and stabilize small Ni nanoparticles and, importantly, expose catalytic sites that are less prone to accumulate ethanol decomposition products (acetate species), as proven by in situ diffuse reflectance infrared Fourier transform spectroscopy.
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24.
  • Chen, Heyin, et al. (författare)
  • Investigating Surface Reactivity of a Ni-Rich Cathode Material toward CO2, H2O, and O2 Using Ambient Pressure X-ray Photoelectron Spectroscopy
  • 2023
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:22, s. 11458-11467
  • Tidskriftsartikel (refereegranskat)abstract
    • Layered Ni-rich transition metal oxide materials are considered the most promising cathodes for use in commercial Li-ion batteries. Due to their instability in air, an impurity layer forms during storage under ambient conditions, and this layer increases electrochemical polarization during charging and discharging, which ultimately leads to a lower cycling capacity. In this work, we found that storage of the LiNi0.8Mn0.1Co0.1O2 (NMC 811) material in ultrahigh vacuum (UHV) can restore the surface by reducing the amount of native carbonate species in the impurity layer. In this work, in situ soft X-ray ambient pressure photoelectron spectroscopy is used to directly follow the interaction between common gases found in air and the NMC 811 surface. During gas exposure of the NMC 811 surface to pure CO2, O2, and a mixture of both pure gases, surface-adsorbed CO2 or/and O2 were detected; however, permanent changes could not be identified under UHV after the gas exposure. In contrast, a permanent increase in metal hydroxide species was observed on the sample surface following H2O vapor exposure, and an increased intensity in the carboxylate peak was observed after exposure to a mixture of CO2/O2/H2O. Thus, the irreversible degradation reaction with CO2 is triggered in the presence of H2O (on relevant time scales defined by the experiment). Additional measurements revealed that X-ray irradiation induces the formation of metal carbonate species on the NMC 811 surface under CO2 and H2O vapor pressure.
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25.
  • Chen, Xi, et al. (författare)
  • 2D Silicon-Germanium-Layered Materials as Anodes for Li-Ion Batteries
  • 2021
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:11, s. 12552 -12561
  • Tidskriftsartikel (refereegranskat)abstract
    • To address the volume changes of Si-based and Ge-based anode materials during lithiation and delithiation, two-dimensional (2D) composites like siloxene and germanane have recently been developed. These 2D materials can insert alkali cations without an alloying reaction, thereby limiting the associated volume expansion. While Si has a high theoretical capacity and low cost, its electrical conductivity is low; on the other hand, Ge provides a higher electronic conductivity but at a higher cost. Therefore, we propose a series of 2D Si-Ge alloys, that is, Si1-xGex with 0.1 < x < 0.9, referred to as siliganes, with reasonable cost and encouraging electrochemical performance. The layered siliganes were obtained by fully deintercalating Ca cations from the Ca(Si1-xGex)2 parent phases and used as Li-ion battery (LIB) anodes. XRD, SEM, Raman spectroscopy, and infrared spectroscopy were used to characterize the materials and identify the mechanisms occurring during cycling in LIBs. Siligane_Si0.9Ge0.1 was identified as the best candidate; at a current density of 0.05 A g-1, after 10 cycles, it showed a reversible capacity of 1325 mA h g-1, with high capacity retention and coulombic efficiency.
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26.
  • Cheng, Haoliang, et al. (författare)
  • Atomic Layer Deposition of SnO2 as an Electron Transport Material for Solid-State P-type Dye-Sensitized Solar Cells
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:10, s. 12022-12028
  • Tidskriftsartikel (refereegranskat)abstract
    • Tin oxide (SnO2) as an electron transport material was prepared by atomic layer deposition in dye-sensitized NiO films to fabricate solid-state p-type dye-sensitized solar cells using two organic dyes PB6 and TIP as photosensitizers. Due to the excellent electron mobility and satisfactory penetration of SnO2 material into the NiO film, a record photocurrent density over 1 mA cm–2 was achieved with a power conversion efficiency of 0.14%. The effect of an inserted Al2O3 layer between the dye-sensitized NiO and SnO2 layer on photovoltaic performance of the devices was also investigated. The results suggest that the charge recombination between NiO and SnO2 can be significantly suppressed, showing prolonged charge lifetime and enhanced photovoltage.
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27.
  • Comparotto, Corrado, et al. (författare)
  • Chalcogenide Perovskite BaZrS3 : Thin Film Growth by Sputtering and Rapid Thermal Processing
  • 2020
  • Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:3, s. 2762-2770
  • Tidskriftsartikel (refereegranskat)abstract
    • Tandem solar cells based on hybrid organic-inorganic metal halide perovskites have reached efficiencies up to 28%, but major concerns for long-term stability and the presence of Pb have raised interest in searching for fully earth-abundant, intrinsic chemically stable, and nontoxic alternatives. With a direct band gap around 1.8 eV and stability in air up to at least 500 degrees C, BaZrS3 is a promising candidate. This work presents the first approach of synthesizing a thin film of such compound by sputtering at ambient temperature with a subsequent rapid thermal process. Despite the short fabrication time, the width of the XRD diffraction peaks and the energy and distribution of the photoluminescence response show comparable crystalline quality to that from bulk synthesis methods. Good crystallization required around 900 degrees C. Such a high temperature could be incompatible with fabrication of tandem solar cells.
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28.
  • Comparotto, Corrado, et al. (författare)
  • Synthesis of BaZrS3 Perovskite Thin Films at a Moderate Temperature on Conductive Substrates
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:5, s. 6335-6343
  • Tidskriftsartikel (refereegranskat)abstract
    • Chalcogenide perovskites are being considered for various energy conversion applications, not least photovoltaics. BaZrS3 stands out for its highly stable, earth-abundant, and nontoxic nature. It exhibits a very strong light-matter interaction and an ideal band gap for a top subcell in a two-junction photovoltaic device. So far, thin-film synthesis-necessary for proper optoelectronic characterization as well as device integration-remains underdeveloped. Sputtering has been considered, among others, but the need for an annealing step of at least 900 degrees C has been a cause for concern: such a high temperature could lead to damaging the bottom layers of prospective tandem devices. Still, a solid-state fabrication route has already demonstrated that BaZrS3 can form at much lower temperatures if excess S is present. In this work, sputtered Ba-Zr precursors capped by SnS are sulfurized at under 600 degrees C for 20 min. Although some Sn is still present at the surface after sulfurization, the resulting crystalline quality is comparable to samples synthesized at much higher temperatures. The results are rationalized, and the effect of key process variables is examined. This study represents the first successful synthesis of BaZrS3 perovskite that is compatible with conductive substrates-an important step forward for device integration.
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29.
  • Dang, Hai Son, et al. (författare)
  • High performing hydroxide exchange membranes with flexible tetra-piperidinium side chains linked by alkyl spacers
  • 2018
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:5, s. 2222-2231
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of the present work is to, in a single material, combine a number of molecular design strategies that have proven successful in the preparation of high-performance anionexchange membranes (AEMs) for alkaline fuel cells. Hence, we here report on highly conductive and alkali-stable poly(phenylene oxide)s carrying flexible side chains attached via alkyl spacer units, where each side chain contains four quaternary piperidinium (QPip) cations with interconnecting alkyl chain segments. These materials are completely soluble in, e.g., methanol and form mechanically tough transparent AEMs with efficiently segregated ions, as indicated by X-ray scattering. At 80 °C, the hydroxide ion conductivity reaches up to 170 and 221 mS cm-1 at ion exchange capacities (IECs) of 2.1 and 2.6 mequiv g-1, respectively. Taking into account the IEC value and water uptake, the tetra-QPip side chain AEMs are found to be significantly more efficient hydroxide ion conductors than corresponding AEMs with mono-QPip side chains. Both the IEC value and hydroxide conductivity of the AEMs show a minor decrease after storage in 1 M aq NaOH at 90 °C during 240 h. However, this decline is not associated with any ionic loss or polymer structure degradation, as confirmed by 1H NMR spectroscopy and thermogravimetrical analysis, even after 380 h storage under the same conditions.
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30.
  • Danyliv, Olesia, et al. (författare)
  • Self-Standing, Robust Membranes Made of Cellulose Nanocrystals (CNCs) and a Protic Ionic Liquid : Toward Sustainable Electrolytes for Fuel Cells
  • 2021
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society. - 2574-0962. ; 4:7, s. 6474-6485
  • Tidskriftsartikel (refereegranskat)abstract
    • Energy-conversion devices based on the phenomenon of proton conduction, for example, polymer electrolyte membrane fuel cells (PEMFCs), require low cost and sustainable electrolytes with high ionic conductivity and good mechanical properties under anhydrous conditions and at temperatures up to 150 °C. Biopolymers possess an intrinsic thermomechanical stability but an insufficient proton conductivity in the dry state, which however may be imparted by a protic ionic liquid (PIL). This work presents the preparation and properties of composite membranes made of cellulose nanocrystals (CNCs) and a PIL. The membranes are thermally stable and display an ionic conductivity within the range 10-4-10-3 S/cm for temperatures between 120 and 160 °C. Moreover, the analysis of the biopolymer's apparent dimensions at nanoscale reveals a dependence of the CNCs' defects, twisting, and aggregation in the presence of the PIL. Preliminary tests using a simple fuel cell setup demonstrate a response of the membranes to the inlet of H2 gas, with a generation of electrical current. These findings provide a solid groundwork for further development and future studies of biopolymer/PIL electrolytes for energy applications. © 2021 The Authors.
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31.
  • Das, Prasanna, et al. (författare)
  • Near-UV-to-Near-IR Hyperbolic Photonic Dispersion in Epitaxial (Hf,Zr)N/ScN Metal/Dielectric Superlattices
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 5:4, s. 3898-3904
  • Tidskriftsartikel (refereegranskat)abstract
    • Hyperbolic metamaterials (HMMs) with extreme dielectric anisotropy have shown great promise in nanophotonic applications such as superlensing, enhancement of spontaneous emission, negative refraction, and the diverging photonic density of states. Noble metal-based metal/dielectric multilayers (e.g., Au/ SiO2 and Ag/TiO2) and metallic (Au and Ag) nanowires embedded inside a dielectric matrix have been traditionally used to demonstrate HMM properties and for implementations into devices. Noble metals are, however, unstable at high temperatures, complementary metal oxide semiconductor incompatible, and difficult to deposit in thin-film form due to their high surface energies that limit their potential applications. TiN has emerged as an alternative plasmonic material to Au in recent years, and epitaxial TiN/Al0.72Sc0.28N metal/semiconductor superlattices were developed that exhibit excellent HMM properties. As TiN exhibits epsilon-near-zero (ENZ) at similar to 500 nm, TiN/Al0.72Sc0.28N HMM also operates from similar to 500 nm to long-wavelength regions. However, for several energy-conversion-related applications as well as for fundamental studies, it is desirable to achieve HMM wavelengths from the near-UV to the near-IR region of the spectrum. In this article, we demonstrate hyperbolic photonic dispersion in (Hf,Zr)N/ScN, a class of metal/semiconducting superlattice metamaterial that covers the near-UV to the near-IR spectral range. Epitaxial HfN/ScN, ZrN/ScN, and Hf0.5Zr0.5N/ScN superlattices are deposited on (001) MgO substrates and characterized with synchrotron-radiation X-ray diffraction as well as high-resolution electron microscopy techniques. Superlattices grow with cube-on-cube epitaxy and with sharp interfaces. Optical characterization reveals both type-I and type-II hyperbolic photonic dispersions as well as low losses and high figures-of-merit. Along with its high-temperature thermal stability, demonstration of HMM properties in (Hf,Zr)N/ScN metal/dielectric superlattices makes them potential candidates for HMM devices.
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32.
  • Das, Tisita, et al. (författare)
  • Functionalization and Defect-Driven Water Splitting Mechanism on a Quasi-Two-Dimensional TiO2 Hexagonal Nanosheet
  • 2019
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 2:7, s. 5074-5082
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, we have dealt with the functionalization of a newly reported quasi-2D hexagonal nanosheet (HNS) of titanium dioxide (TiO2) for photocatalytic water splitting to generate hydrogen and oxygen. Functionalization has been carried out by creating a single oxygen vacancy defect as well as by incorporating substitutional doping with C, N, P, and S atoms at the O site of TiO2 HNS. The effects of functionalization and vacancy defects on the structural and electronic properties of HNS have been investigated by determining the corresponding projected density of states. It has been observed that functionalization causes a shift in the VBM and CBM of HNS, which in principle influences the catalytic activity. In addition, we have determined the work function for these materials in order to correlate them with the electrochemical activities of different considered HNSs. The catalytic activity has been predicted by determining the reaction coordinate as constructed from the free energies of the different reaction intermediates involved in HER and OER Among all of the systems that we have studied, HNS with an oxygen monovacancy has emerged as the best possible candidate for the water-splitting mechanism.
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33.
  • Delekta, Szymon Sollami, et al. (författare)
  • Wet Transfer of Inkjet Printed Graphene for Microsupercapacitors on Arbitrary Substrates
  • 2019
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 2:1, s. 158-163
  • Tidskriftsartikel (refereegranskat)abstract
    • Significant research interest is being devoted to exploiting the properties of graphene but the difficult integration on various substrates limits its use. In this regard, we developed a transfer technique that allows the direct deposition of inkjet printed graphene devices on arbitrary substrates, even 3D objects and living plants. With this technique, we fabricated micro-supercapacitors, which exhibited good adhesion on almost all substrates and no performance degradation induced by the process. Specifically, the microsupercapacitor on an orchid leaf showed an areal capacitance as high as 441 mu F cm(-2) and a volumetric capacitance of 1.16 F cm(-3). This technique can boost the use of graphene in key technological applications, such as self powered epidermal electronics and environmental monitoring systems.
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34.
  • Deshpande, Swapnil S., et al. (författare)
  • Carbon Nitride Monolayers as Efficient Immobilizers toward Lithium Selenides : Potential Applications in Lithium-Selenium Batteries
  • 2021
  • Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 4:4, s. 3891-3904
  • Tidskriftsartikel (refereegranskat)abstract
    • The low cost, high energy density, and nontoxic nature have made lithium-selenium batteries (LiSeBs) a promising option for large-scale energy storage applications. However, the issue of capacity loss during consecutive charge/discharge cycles has put a serious question mark on the commercialization of LiSeBs. In a quest to suppress the issue of capacity loss due to the dissolution of active lithium polyselenides (Li2Sen, n = 1-8) into the electrolyte, the so-called shuttle effect, we have employed first-principles density functional theory calculations to study the anchoring properties of two carbon nitrides monolayers, namely, nitrogenated holey graphene (C2N) and carbon nitride (C3N). We find that the presence of nitrogen (N) atoms, in both C2N and C3N, enable them to bind Li2Sen clusters stronger than that of graphene. We further discover that the anchoring properties of C2N (-2.03 to -3.82 eV) are stronger than that of C3N (-1.21 to -1.30 eV) due to higher concentrations of N atoms and relatively bigger pore size in the former than the later. In addition to the appropriate bindings, improved conductivities upon the adsorption Li2Sen further reinforce the promise of C2N and C3N as potential anchoring materials for LiSeBs. We believe that our computational results would pave the way toward the experimental synthesis of efficient anchoring materials based on the studied systems.
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35.
  • Dürr, Robin N., et al. (författare)
  • Robust and Efficient Screen-Printed Molecular Anodes with Anchored Water Oxidation Catalysts
  • 2021
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:10, s. 10534-10541
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, we present the preparation and performance of screen-printed anodes for electrochemical water splitting in neutral media. With the combination of printed electrodes and molecular water oxidation catalysts, we successfully take advantage of a low-cost and up-scalable fabrication method of graphitic electrodes with the outstanding catalytic activity and stability of oligomeric ruthenium-based molecular water oxidation catalysts, offering a promising electroanode for water oxidation applications.
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36.
  • Endrodi, Balazs, et al. (författare)
  • One-Step Electrodeposition of Nanocrystalline TiO2 Films with Enhanced Photoelectrochemical Performance and Charge Storage
  • 2018
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:2, s. 851-858
  • Tidskriftsartikel (refereegranskat)abstract
    • With the rapid development of renewable energy technologies there is an urgent need to find synthesis routes that address the needs of materials in a reproducible and affordable way. In this study, we present a one-step electrochemical method for the deposition of nanocrystalline titanium dioxide films on different carbon substrates. By optimizing the synthetic conditions, electrodeposition of nanocrystalline and porous titanium dioxide layers was achieved in only a few minutes. To deconvolute the complex effect of the solution pH and temperature, as well as the deposition potential, a set of systematic experiments was carried out on glassy carbon electrodes. The robustness and general applicability of this synthetic approach is demonstrated by extending it to graphene film electrodes. The phase composition of TiO2 was controlled by varying the solution composition. The photoelectrochemical performance of the electrodeposited titanium dioxide films was better than, or at least comparable to the benchmark P25 titanium dioxide films. Hydrogen-ion intercalation measurements for the TiO2/graphene electrodes indicated promising charge storage capacity, which might be exploited in the future in Li-ion batteries.
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37.
  • Escobar Steinvall, Simon, et al. (författare)
  • Nanoscale Growth Initiation as a Pathway to Improve the Earth-Abundant Absorber Zinc Phosphide
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:5, s. 5298-5306
  • Tidskriftsartikel (refereegranskat)abstract
    • Growth approaches that limit the interface area between layers to nanoscale regions are emerging as a promising pathway to limit the interface defect formation due to mismatching lattice parameters or thermal expansion coefficient. Interfacial defect mitigation is of great interest in photovoltaics as it opens up more material combinations for use in devices. Herein, an overview of the vapor-liquid-solid and selective area epitaxy growth approaches applied to zinc phosphide (Zn3P2), an earth-abundant absorber material, is presented. First, we show how different morphologies, including nanowires, nanopyramids, and thin films, can be achieved by tuning the growth conditions and growth mechanisms. The growth conditions are also shown to greatly impact the defect structure and composition of the grown material, which can vary considerably from the ideal stoichiometry (Zn3P2). Finally, the functional properties are characterized. The direct band gap could accurately be determined at 1.50 ± 0.1 eV, and through complementary density functional theory calculations, we can identify a range of higher-order band gap transitions observed through valence electron energy loss spectroscopy and cathodoluminescence. Furthermore, we outline the formation of rotated domains inside of the material, which are a potential origin of defect transitions that have been long observed in zinc phosphide but not yet explained. The basic understanding provided reinvigorates the potential use of earth-abundant II-V semiconductors in photovoltaic technology. Moreover, the transferrable nanoscale growth approaches have the potential to be applied to other material systems, as they mitigate the constraints of substrate-material combinations causing interface defects.
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38.
  • Fast, Jonatan, et al. (författare)
  • Optical-Beam-Induced Current in InAs/InP Nanowires for Hot-Carrier Photovoltaics
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:6, s. 7728-7734
  • Tidskriftsartikel (refereegranskat)abstract
    • Using the excess energy of charge carriers excited above the band edge (hot carriers) could pave the way for optoelectronic devices, such as photovoltaics exceeding the Shockley-Queisser limit or ultrafast photodetectors. Semiconducting nanowires show promise as a platform for hot-carrier extraction. Proof of principle photovoltaic devices have already been realized based on InAs nanowires, using epitaxially defined InP segments as energy filters that selectively transmit hot electrons. However, it is not yet fully understood how charge-carrier separation, relaxation, and recombination depend on device design and on the location of optical excitation. Here, we introduce the use of an optical-beam-induced current (OBIC) characterization method, employing a laser beam focused close to the diffraction limit and a high precision piezo stage, to study the optoelectric performance of the nanowire device as a function of the position of excitation. The photocurrent response agrees well with modeling based on hot-electron extraction across the InP segment via diffusion. We demonstrate that the device is capable of producing power and estimate the spatial region within which significant hot-electron extraction can take place to be on the order of 300 nm away from the barrier. When comparing to other experiments on similar nanowires, we find good qualitative agreement, confirming the interpretation of the device function, while the extracted diffusion length of hot electrons varies. Careful control of the excitation and device parameters will be important to reach the potentially high device performance theoretically available in these systems.
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39.
  • Franchi, Daniele, et al. (författare)
  • Effect of the Ancillary Ligand on the Performance of Heteroleptic Cu(I) Diimine Complexes as Dyes in Dye-Sensitized Solar Cells
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:2, s. 1460-1470
  • Tidskriftsartikel (refereegranskat)abstract
    • A series of heteroleptic Cu(I) diimine complexes with different ancillary ligands and 6,6'-dimethyl-2,2'-bipyridine-4,4'-dibenzoic acid (dbda) as the anchoring ligand were selfassembled on TiO2 surfaces and used as dyes for dye-sensitized solar cells (DSSCs). The binding to the TiO2 surface was studied by hard X-ray photoelectron spectroscopy for a brominecontaining complex, confirming the complex formation. The performance of all complexes was assessed and rationalized on the basis of their respective ancillary ligand. The DSSC photocurrent-voltage characteristics, incident photon-to-current conversion efficiency (IPCE) spectra, and calculated lowest unoccupied molecular orbital (LUMO) distributions collectively show a push-pull structural dye design, in which the ancillary ligand exhibits an electron-donating effect that can lead to improved solar cell performance. By analyzing the optical properties of the dyes and their solar cell performance, we can conclude that the presence of ancillary ligands with bulky substituents protects the Cu(I) metal center from solvent coordination constituting a critical factor in the design of efficient Cu(I)-based dyes. Moreover, we have identified some components in the I-/I-3(-)-based electrolyte that causes dissociation of the ancillary ligand, i.e., TiO2 photoelectrode bleaching. Finally, the detailed studies on one of the dyes revealed an electrolyte-dye interaction, leading to a dramatic change of the dye properties when adsorbed on the TiO2 surface.
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40.
  • Francon, Hugo, et al. (författare)
  • Toward Li-ion Graphite Anodes with Enhanced Mechanical and Electrochemical Properties Using Binders from Chemically Modified Cellulose Fibers
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:8, s. 9333-9342
  • Tidskriftsartikel (refereegranskat)abstract
    • Cellulose nanofibers (CNFs) are bio-sourced nanomaterials, which, after proper chemical modification, exhibit a unique ability to disperse carbon-rich micro- and nanomaterials and can be used in the design of mechanically strong functional nanocomposites. When used in the preparation of graphite anodes for Li-ion batteries, they have the potential to outperform conventional binders such as carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) both electrochemically and mechanically. In this study, cellulose-rich fibers were subjected to three different chemical modifications (including carbonyl-, carboxyl-, and aldehyde-functionalization) to facilitate their fibrillation into CNFs during the preparation of aqueous slurries of graphite and carbon black. Using these binders, graphite anodes were prepared through conventional blade coating. Compared to CMC/SBR reference anodes, all anodes prepared with modified cellulosic fibers as binders performed better in the galvanostatic cycling experiments and in the mechanical cohesion tests they were subjected to. Among them, the aldehyde- and carboxyl-rich fibers performed the best and resulted in a 10% increase in specific capacity with a simultaneous two- and three-fold increase of the electrode material's stress-at-failure and strain-at-break, respectively. In-depth characterizations attributed these results to the distinctive nanostructure and surface chemistry of the composites formed between graphite and these fiber-based binders. 
  •  
41.
  • Gao, Jiajia, et al. (författare)
  • Exploring Lewis-Base Effects to Improve the Efficiency of [Co(bpy)(3)](2+/3+)-Mediated Dye-Sensitized Solar Cells
  • 2020
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:6, s. 5705-5711
  • Tidskriftsartikel (refereegranskat)abstract
    • The state-of-the-art cobalt(II/III) tris(bipyridyl) redox shuttles open a chapter for pursuing highly efficient dye-sensitized solar cells (DSSCs). Previous work has demonstrated that light exposure of the Co(III) along with the Lewis base additive, tert-butylpyridine (TBP), effectively improves the solar cell efficiency. With this as a platform, a new Lewis base, i.e., tert-butylpyridine N-oxide (TBP-O), is introduced as an electrolyte co-additive instead of TBP alone. The resulting D3S-sensitized solar cells exhibit an efficiency of 6.6% at full solar illumination, which further increases to 8.1% by exposing the new electrolyte mixture to the light and thus outperforms typical Li+-containing DSSCs. A mechanism with regard to the interactions between Co(III) and Lewis base additives supported by electrochemical and spectroscopic studies is suggested to explain the performance improvement. The study illustrates negative effects of TBP on the charge- and mass-transfer kinetics at the electrode/electrolyte interface and reveals that the effects are eliminated by a light-induced reaction between Co(III) and TBP-O.
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42.
  • Gimpel, Thomas, et al. (författare)
  • Electrochemical Carbon Dioxide Reduction on Femtosecond Laser-Processed Copper Electrodes : Effect on the Liquid Products by Structuring and Doping
  • 2021
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:6, s. 5927-5934
  • Tidskriftsartikel (refereegranskat)abstract
    • A femtosecond laser process is presented increasing the surface area of copper electrocatalysts for an electrochemical CO2 reduction reaction (CO2RR). The laser treatment allows us to tune the surface morphology and the chemical composition of the copper electrocatalysts. This tunability is used to correlate the role of the surface area and catalyst dopants with the selectivity of the CO2RR. The liquid products of the CO2RR are monitored through ex situ nuclear magnetic resonance spectroscopy. The products’ distribution shows that the electrode surface area plays a key role in the electrochemical conversion of CO2 into multicarbon liquid products. We show that sulfur dopants boost the production of formate. Remarkably, by co-doping sulfur and fluoride, we show that the chalcogenide dopant counteracts the known boosting effect of fluoride to convert CO2 into multicarbon products. Oxygen doping in the range of 2–19 atom % does not significantly affect the distribution of liquid products from CO2 electroreduction. In a broad perspective, this work highlights the potential of the femtosecond laser process to fine-tune surfaces to produce photo- and electrocatalyst materials.
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43.
  • Gradzka-Kurzaj, Iwona, et al. (författare)
  • Molecular Water Oxidation Catalysis : Characterization of Subnanosecond Processes and Ruthenium "Green Dimer" Formation
  • 2021
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:3, s. 2440-2450
  • Tidskriftsartikel (refereegranskat)abstract
    • Dye-sensitized photoelectrochemical cells were prepared with popular ruthenium sensitizer (RuP) and ruthenium catalyst (RuCAT) coadsorbed on mesoporous titania. The cells were studied in 0.1 M Na2SO4(aq) by spectroscopic methods, including femtosecond transient absorption spectroscopy. The formation of RuCAT dimer can be observed by the naked eye due to the change of color from dark-red to green. The dimer displays a characteristic absorption feature with lambda(max) approximate to 670-680 nm and its formation was found to be accelerated upon irradiation. Electron injection from RuP into titania occurs partially from the excited singlet state decaying on the ultrafast time scale (<0.2 ps) and partially from the triplet state with a time constant of several tens of ps. The decay of the excited RuCAT dimer takes place with a main component of about 1 ps. The quenching of the oxidized RuP by electron transfer from RuCAT is observed with a time constant 150-200 ps and is independent of the excitation fluence. This fast first step of catalyst oxidation further explains the chronoamperometry data recorded for photoanodes made of coadsorbed RuP and RuCAT. Finally, RuCAT in solution shows a remarkable short lifetime of the excited state, with a longest component of about 20 ps.
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44.
  • Gugole, Marika, 1993, et al. (författare)
  • Comparison of Electrodeposited and Sputtered Tungsten Trioxide Films for Inorganic Electrochromic Nanostructures
  • 2023
  • Ingår i: ACS Applied Optical Materials. - : American Chemical Society (ACS). - 2771-9855 .- 2574-0962. ; 1:2, s. 558-568
  • Tidskriftsartikel (refereegranskat)abstract
    • Electrochromic materials and their implementation with structural colors are currently being intensely researched because of their promising applications as non-emissive display devices utilizing ambient light. In particular, several fully inorganic devices that rely on electrochromic tungsten trioxide (WO3) have been presented. For preparing nanoscale films of this material, sputtering is the most established technique, but electrodeposition has recently been shown to be capable of achieving exceptionally high electro-optical modulation contrast without the need for expensive equipment. In this work, we investigate the possibilities of electrodeposited WO3 and present a systematic comparison with sputtered WO3 with respect to performance in electrochromic devices. Importantly, we show that “ultralarge” electro-optical modulation (∼95% change in transmission) is possible for both types of films. However, it is only the sputtered films that enable such high contrast in a stable electrolyte such as LiClO4 in propylene carbonate. The electrodeposited films are less uniform and difficult to make thicker than ∼500 nm. We find no evidence that the electrochromic properties of the electrodeposited WO3 are intrinsically better than those of sputtered WO3. However, the electrodeposited films are much rougher and/or porous on the nanoscale, which increases the switching speed considerably. We conclude that electrodeposited WO3 is mainly useful in applications in which high contrast is not essential while switching speed is. As an example, we present the first electrodeposited WO3 integrated with structural colors by sandwiching the material between two metal films. By electrical control, the reflective colors can then be tuned at least one order of magnitude faster (a few seconds) than previously reported while having fair color quality and without any loss of brightness.
  •  
45.
  • Gustafsson, Olof, et al. (författare)
  • Low-Temperature Cation Ordering in High Voltage Spinel Cathode Material
  • 2023
  • Ingår i: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 6:9, s. 5000-5008
  • Tidskriftsartikel (refereegranskat)abstract
    • The spinel cathode LiNi0.5Mn1.5O4 (LNMO) is a promising material for battery applications; however, issues regarding its cycling stability need to be addressed to fully utilize its potential. Specifically, LNMO suffers from rapid capacity loss following prolonged electrochemical cycling where the capacity drop occurs at an earlier stage for its transition metal ordered form. Further, the disordered form has been found to partially order during cycling, leading to the question if the failing of the disordered form is driven by Ni and Mn ordering in the structure. However, ordering is usually initiated at temperatures above 700 degrees C in the fully lithiated state, sparking the question if the energy barrier for the ordering process is lowered at the reduced Li content. In the work presented here, in situ neutron diffraction was used to further elucidate the ordering temperature and thermal stability of LixNi0.5Mn1.5O4 (0.000 (10) < x < 0.675 (10)). The temperature for Ni and Mn ordering was found to be dramatically lowered to 310-320 degrees C for LixNi0.5Mn1.5O4 compositions of 0.222 (8) < x < 0.675 (10), explained by a lower energy barrier for formation of intermediate Frenkel defect states. Li ordering and a lowering of symmetry to P213, together with formation of both a NiMn2O4-type spinel phase and a NiMnO3-type phase, could also be observed. The formation of NiMn2O4- and NiMnO3-type phases could be linked to reorganization of transition metals (TM) within the spinel structure and were found to be in competition with Ni and Mn ordering. At higher Li contents, transition metal diffusion tended to favor Ni and Mn ordering, while NiMn2O4- and NiMnO3-type phases were formed to a greater extent at lower Li contents. These results highlight the importance of suppressing transition metal reorganization in LiNi0.5Mn1.5O4, via increased TM diffusion energy barriers, as a key strategy for minimizing structural rearrangements and ultimately improving its electrochemical cyclability.
  •  
46.
  • Hanauer, S., et al. (författare)
  • Photothermal Conversion of Solar Infrared Radiation by Plasmonic Nanoantennas for Photovoltaic-Thermoelectric Hybrid Devices
  • 2023
  • Ingår i: Acs Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:4, s. 2128-2133
  • Tidskriftsartikel (refereegranskat)abstract
    • Photovoltaics have become one of the low-cost options for electricity generation. However, the lack of absorption of the near-infrared and infrared solar spectrum intrinsically limits its efficiency. Here, we present an approach for photothermal conversion of solar infrared radiation in photovoltaic-thermoelectric systems using plasmonic nanoantennas. Through numerical calculations-driven shape engineering, we identified Ni diabolo nanoantennas as efficient solar infrared spectrum harvesters. Nanofabrication with electron-beam lithography further revealed its impact on nanoantenna optical properties at the single-nanoantenna level. In the large-scale low-cost approach, however, photothermal surfaces of nanocone plasmonic antennas, made with a simple and robust fabrication process, still deliver a significant 6.1 degrees C temperature increase under solar infrared illumination. The reported results pave the way toward the development of hybrid photovoltaic-thermoelectric systems with an optimal utilization of the solar spectrum.
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47.
  • He, Lanlan, et al. (författare)
  • Insights into the Explicit Mechanism and Dynamic Rate of Regeneration of Sensitizing Organic Dyes by Transition-Metal Redox Mediators in Solar Cells Using Ab Initio Molecular Dynamics
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:12, s. 14638-14645
  • Tidskriftsartikel (refereegranskat)abstract
    • Ab initio molecular dynamics simulations were employed to investigate the regeneration of the oxidized organic dye LEG4+by the reducing agents Fc0and Co[(bpy)3]2+. Dynamical Mulliken spin population analyses suggest that the oxidized LEG4+may be regenerated by Fc0and Co[(bpy)3]2+directly in specific configurations providing that the Fe2+and Co2+are in a low-spin state. An exponential coupling relation was found between the distance between the dye and the redox mediators. The rate of the LEG4+regeneration by Fc0and Co[(bpy)3]2+ranges between 5.41 μs-1∼3.80 ps-1and 0.58 μs-1∼0.04 ps-1, respectively, which spans the window of all experimentally reported rates.
  •  
48.
  • Hedman, Jonas, et al. (författare)
  • Fiber Optic Monitoring of Composite Lithium Iron Phosphate Cathodes in Pouch Cell Batteries
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:1, s. 870-881
  • Tidskriftsartikel (refereegranskat)abstract
    • - Developing techniques for real-time monitoring of the complex and dynamic environment in lithium-ion batteries is crucial for optimal use of the cells and to develop the next generation of batteries. In this work, we demonstrate the use of fiber optic evanescent wave (FOEW) sensors for monitoring lithium iron phosphate (LFP) composite cathodes in pouch cells. The fiber optic sensors were placed on top of the LFP electrodes, and the pouch cells were found to cycle well with significantly improved electrochemical performance compared to fully embedded fibers in Swagelok cells. Galvanostatic, voltammetric, and pulsed current techniques demonstrated that the optical response correlated well with the capacity, and a clear difference in sensor response was seen when the sensors were placed at the surface of composite electrodes compared to fibers embedded in the cathode. The optical response from LFP at different rates was also investigated, but no apparent influence on intensity output was found even though polarization was observed in the voltage profiles at higher currents. It was also demonstrated that the electrolyte itself functioned as a fiber cladding and that the salt concentration in the electrolyte did not influence the optical signal. In addition, given the short penetration depth of the evanescent waves, the sensor response is most likely dominated by the surface conditions of electrode particles near the sensing region. These findings provide further insight into the application and performance of FOEW sensors integrated into batteries, as well as the possibility of developing low-cost fiber optic sensors for battery monitoring under working conditions.
  •  
49.
  • Hedman, Jonas, et al. (författare)
  • Fiber Optic Sensors for Detection of Sodium Plating in Sodium-Ion Batteries
  • 2022
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:5, s. 6219-6227
  • Tidskriftsartikel (refereegranskat)abstract
    • Optical fiber sensors integrated into sodium-ion batteries could provide a battery management system (BMS) with information to identify early warning signs of plating, preventing catastrophic failure and maintaining safe operation during fast charging. This work shows the possibility of directly detecting plating of sodium metal in electrochemical cells by means of operando fiber optic evanescent wave (FOEW) spectroscopy. The results include measurements with FOEW sensors on bare copper substrates as well as on hard carbon anodes during operation in both half- and full-cell configurations. Full cells using hard carbon anodes and Prussian white cathodes with high areal capacities (>1.5 mAh cm(-2)) and integrated FOEW sensors are shown to cycle well in pouch cells. The results also include measurements to demonstrate plating on hard carbon during sodiation at different rates.
  •  
50.
  • Honarfar, Alireza, et al. (författare)
  • Photoexcitation dynamics in electrochemically charged CdSe quantum dots : From hot carrier cooling to auger recombination of negative trions
  • 2020
  • Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:12, s. 12525-12531
  • Tidskriftsartikel (refereegranskat)abstract
    • Fulfilling the potential of colloidal semiconductor quantum dots (QDs) in electrically driven applications remains a challenge largely since operation of such devices involves charged QDs with drastically different photophysical properties compared to their well-studied neutral counterparts. In this work, the full picture of excited state dynamics in charged CdSe QDs at various time scales has been revealed via transient absorption spectroscopy combined with electrochemistry as a direct manipulation tool to control the negative charging of CdSe QDs. In trions, excited states of single charged QDs, the additional electron in the conduction band speeds up the hot electron cooling by enhanced electron-electron scattering followed by charge redistribution and polaron formation in a picosecond time scale. The trions are finally decayed by the Auger process in a 500 ps time scale. Double charging in QDs, on the other hand, decelerates the polaron formation process while accelerates the following Auger decay. Our work demonstrates the potential of photoelectrochemistry as a platform for ultrafast spectroscopy of charged species and paves the way for further studies to develop comprehensive knowledge of the photophysical processes in charged QDs more than the well-known Auger decay, facilitating their use in future optoelectronic applications.
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