| 1. |
- Aktekin, Burak, et al.
(author)
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How Mn/Ni Ordering Controls Electrochemical Performance in High-Voltage Spinel LiNi0.44Mn1.56O4 with Fixed Oxygen Content
- 2020
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In: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:6, s. 6001-6013
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Journal article (peer-reviewed)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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| 2. |
- Ali, Amjad, et al.
(author)
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Electrochemical Analysis of a Titanate-Based Anode for Direct Carbon Fuel Cells
- 2020
-
In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:9, s. 9182-9189
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Journal article (peer-reviewed)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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| 3. |
- Chai, Zhigang, et al.
(author)
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Ni–Ag Nanostructure-Modified Graphitic Carbon Nitride for Enhanced Performance of Solar-Driven Hydrogen Production from Ethanol
- 2020
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:10, s. 10131-10138
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Journal article (peer-reviewed)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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| 4. |
- Comparotto, Corrado, et al.
(author)
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Chalcogenide Perovskite BaZrS3 : Thin Film Growth by Sputtering and Rapid Thermal Processing
- 2020
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In: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:3, s. 2762-2770
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Journal article (peer-reviewed)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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| 5. |
- Gao, Jiajia, et al.
(author)
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Exploring Lewis-Base Effects to Improve the Efficiency of [Co(bpy)(3)](2+/3+)-Mediated Dye-Sensitized Solar Cells
- 2020
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:6, s. 5705-5711
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Journal article (peer-reviewed)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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| 6. |
- Honarfar, Alireza, et al.
(author)
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Photoexcitation dynamics in electrochemically charged CdSe quantum dots : From hot carrier cooling to auger recombination of negative trions
- 2020
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:12, s. 12525-12531
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Journal article (peer-reviewed)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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| 7. |
- Hu, Wei, et al.
(author)
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Axisymmetric and Asymmetric Naphthalene-Bisthienothiophene Based Nonfullerene Acceptors: On Constitutional Isomerization and Photovoltaic Performance
- 2020
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:6, s. 5734-5744
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Journal article (peer-reviewed)abstract
- Two pairs of constitutional isomers of fused-octacyclic nonfullerene acceptors (NFAs) based on a naphthalene-bisthienothiophene core with or without fluorination at the ending groups have been developed. Compared with the axisymmetric NFAs N66-IC and N66-2FIC with two six-member-ring bridges, their asymmetric constitutional isomers N65-IC and N65-2FIC both with one six-member-ring bridge and one five-member-ring bridge exhibit remarkable red-shifted absorption, higher crystallinity, and slightly down-shifted LUMO energy levels. Organic solar cells based on PBDB-T-2F:N65-2FIC achieved a promising power conversion efficiency of 10.19%, which is three times higher than that of its counterpart PBDB-T-2F:N66-2FIC cell (3.46%). While being blended with PBDB-T as the donor material, the asymmetric acceptor analogue N65-IC based solar cell pronounces a PCE of 9.03%, being significantly improved from that of 5.45% for the PBDB-T:N66-IC based cell, which is in consistency with the results from those cells from their both fluorinated donor and acceptor counterparts. Design rules on either both fluorinated, both nonfluorinated, or cross-combined donor/acceptors for device fabrication has been explored. In addition, PBDB-T-2F:N65-2FIC possesses very promising device stability with 85% of its initial PCE after an exposure time of 1500 h under one sun illumination, which is meaningful for their future commercial devices.
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| 8. |
- Jian, Jingxin, et al.
(author)
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Cu2O/ZnO p-n Junction Decorated with NiOx as a Protective Layer and Cocatalyst for Enhanced Photoelectrochemical Water Splitting
- 2020
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In: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:11, s. 10408-10414
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Journal article (peer-reviewed)abstract
- Cuprous oxide (Cu2O) has attracted much interest as a photocathode for photoelectrochemical (PEC) water splitting because of its elemental abundance and the favorable band gap, but its poor stability in aqueous solutions hinders the practical PEC application. Compared to the mostly used TiO2 and noble metal cocatalysts for coating the Cu2O photocathode, this work demonstrates a strategy to fabricate a noble metal-free photocathode. We construct a Cu2O/ZnO p-n junction photocathode decorated with the NiOx layer as both the protective layer and the hydrogen evolution reaction (HER) cocatalyst. The NiOx cocatalyst exhibits a small Tafel slope of 35.9 mV/dec and a very low overpotential of 115 mV to drive a current of 10 mA/cm(2), which are very close to the HER activity of the noble metal platinum. With decorated NiOx the Cu2O/ZnO/NiOx photocathode exhibits significantly improved stability and photocurrent density with a Faradaic efficiency of H-2 gas evolution of 95 +/- 4%, distinctly outperforming the Cu2O, Cu2O/ZnO, and Cu2O/ZnO/TiO2 photocathodes. Moreover, electrochemical impedance analysis evidenced that NiOx as a cocatalyst also facilitates the transfer of photogenerated electrons across the electrode/electrolyte interface for water reduction. This work demonstrates that NiOx is not only a stable protective layer against corrosion but also a highly active H-2 evolution cocatalyst. These findings provide new insights for the design of noble metal-free photocathodes toward solar fuel development.
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| 9. |
- Khossossi, Nabil, et al.
(author)
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Rational Design of 2D h-BAs Monolayer as Advanced Sulfur Host for High Energy Density Li-S Batteries
- 2020
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 3:8, s. 7306-7317
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Journal article (peer-reviewed)abstract
- The emergence of compact lithium-sulfur (Li-S) batteries with improved performances is becoming one of the most desirable aspects of future energy technologies. Beyond Li-ion batteries, Li-S is of great relevance to follow as it adapts to the specificity of each application. It is among the most suitable elements for high-performance energy storage systems, given its high theoretical capacity (1674 mA h g(-1)) and energy density (2600 W h kg(-1)) relative to Li-ion batteries (300 W h kg(-1)). Nevertheless, the high-cell polarization and the shuttle effect constitute an enormous challenge toward the concrete applications of Li-S batteries. In the framework of this work, density functional theory calculations have been carried out to analyze the potential of h-BAs nanosheets as a promising host material for Li-S batteries. Binding and electronic characteristics of lithium polysulfides (LiPSs) adsorbed on h-BAs surface have been explored. Reported findings highlight the potential of the hBAs monolayer as a moderate host material, given that the binding energies of different LiPSs vary from 0.47 to 3.55 eV. More detailed analysis of the complex binding mechanisms is carried out by investigating the components of van der Waals physical/chemical interactions. The defected surface of the h-BAs monolayer has optimum binding energies with LiPSs for Li-S batteries. All these findings provide valuable insights into the binding and electronic characteristics of the h-BAs monolayer as a moderate host material for Li-S batteries.
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| 10. |
- Kim, Eun Jeong, et al.
(author)
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Oxygen Redox Activity through a Reductive Coupling Mechanism in the P3-Type Nickel-Doped Sodium Manganese Oxide
- 2020
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In: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962. ; 3:1, s. 184-191
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Journal article (peer-reviewed)abstract
- Increasing dependence on rechargeable batteries for energy storage calls for the improvement of energy density of batteries. Toward this goal, introduction of positive electrode materials with high voltage and/or high capacity is in high demand. The use of oxygen chemistry in lithium and sodium layered oxides has been of interest to achieve high capacity. Nevertheless, a complete understanding of oxygen-based redox processes remains elusive especially in sodium ion batteries. Herein, a novel P3-type Na0.67Ni0.2Mn0.8O2, synthesized at low temperature, exhibits oxygen redox activity in high potentials. Characterization using a range of spectroscopic techniques reveals the anionic redox activity is stabilized by the reduction of Ni, because of the strong Ni 3d-O 2p hybridization states created during charge. This observation suggests that different route of oxygen redox processes occur in P3 structure materials, which can lead to the exploration of oxygen redox chemistry for further development in rechargeable batteries.
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