| 1. |
- Marra, Eva, et al.
(författare)
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ORR activity and stability of carbon supported Pt3Y thin films in PEMFCs
- 2023
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 472
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate stability of oxygen reduction reaction (ORR) on a Pt3Y thin film under relevant fuel cell conditions, we performed an accelerated stress test (AST) consisting of 3600 potential cycles between 0.4 and 1.4 V at 1 V s−1 in a single proton exchange membrane fuel cell (PEMFC). The ORR activities were evaluated via polarization curves before and after the AST. Electrochemical active surface area (ECSA) was obtained by CO-stripping voltammetry whereas the morphological changes were monitored by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Variations in surface composition and electronic structures were evaluated by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). After AST, the polarization curves show loss of ORR activity in all voltages for both Pt and Pt3Y. Except at very high voltages (E > 0.85 VRHE), the ORR activity of Pt3Y after AST is very close to that of Pt before AST. This correlates well with the results from the deconvolution of Pt-4f XPS spectra where the binding energy of metallic Pt in Pt3Y is comparable to pure Pt (71.22 eV). SEM and TEM images demonstrate that the morphologies of the aged Pt3Y and as-sputtered Pt are similar, whereas EDX results confirm a steady bulk composition of Pt3Y thin films throughout the entire electrochemical test. By correlating all these results, we conclude that the loss of ORR activity for Pt3Y is due to an increase in the thickness of the Pt overlayer which induces a relaxation of the Pt overlayer decreasing the compressive strain effect. For pure Pt, the loss of ORR activity is associated with a growth of the Pt domains associated with Ostwald ripening process.
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| 2. |
- Brown, Rosemary, 1990, et al.
(författare)
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Plasma-Induced Heating Effects on Platinum Nanoparticle Size during Sputter Deposition Synthesis in Polymer and Ionic Liquid Substrates
- 2021
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 37:29, s. 8821-8828
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Tidskriftsartikel (refereegranskat)abstract
- Nanoparticle catalyst materials are becoming ever more important in a sustainable future. Specifically, platinum (Pt) nanoparticles have relevance in catalysis, in particular, fuel cell technologies. Sputter deposition into liquid substrates has been shown to produce nanoparticles without the presence of air and other contaminants and the need for precursors. Here, we produce Pt nanoparticles in three imidazolium-based ionic liquids and PEG 600. All Pt nanoparticles are crystalline and around 2 nm in diameter. We show that while temperature has an effect on particle size for Pt, it is not as great as for other materials. Sputtering power, time, and postheat treatment all show slight influence on the particle size, indicating the importance of temperature during sputtering. The temperature of the liquid substrate is measured and reaches over 150 °C during deposition which is found to increase the particle size by less than 20%, which is small compared to the effect of temperature on Au nanoparticles presented in the literature. High temperatures during Pt sputtering are beneficial for increasing Pt nanoparticle size beyond 2 nm. Better temperature control would allow for more control over the particle size in the future.
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| 3. |
- Brown, Rosemary, 1990, et al.
(författare)
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Surface Composition of a Highly Active Pt3Y Alloy Catalyst for Application in Low Temperature Fuel Cells
- 2020
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Ingår i: Fuel Cells. - : Wiley. - 1615-6846 .- 1615-6854. ; 20:4, s. 413-419
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Tidskriftsartikel (refereegranskat)abstract
- Currently, platinum is the most widely used catalyst for low temperature proton exchange membrane fuel cells (PEMFC). However, the kinetics at the cathode are slow, and the price of platinum is high. To improve oxygen reduction reaction (ORR) kinetics at the cathode, platinum can be alloyed with rare earth elements, such as yttrium. We report that Pt3Y has the potential to be over 2 times more active for the ORR compared with Pt inside a real fuel cell. We present detailed photoemission analysis into the nature of the sputtered catalyst surface, using synchrotron radiation photoelectron spectroscopy (SRPES) to examine if surface adsorbates or impurities are present and can be removed. Pretreatment removes most of the yttrium oxide in the surface leaving behind a Pt overlayer which is only a few monolayers thick. Evidence of a substochiometric oxide peak in the Y 3d core level is presented, this oxide extends into the surface even after Ar+ sputter cleaning in-situ. This information will aid the development of new highly active nanocatalysts for employment in real fuel cell electrodes.
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| 4. |
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| 5. |
- Eriksson, Björn, et al.
(författare)
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Enhanced oxygen reduction activity with rare earth metal alloy catalysts in proton exchange membrane fuel cells
- 2021
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 387
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Tidskriftsartikel (refereegranskat)abstract
- Alloying platinum is an approach to increase the oxygen reduction reaction (ORR) activity and at the same time reduce the amount of precious platinum catalyst in proton exchange membrane fuel cells (PEMFC). In this work the cathode activity of thin films of rare earth metals (REM) alloys, Pt Y, Pt Gd and Pt Tb, produced by sputter deposition onto gas diffusion layers, are evaluated in a fuel cell by means of polarization curves in O /H , and cyclic- and CO-stripping voltammetry in N /5% H . Prior to evaluation, the model electrodes were acid-treated to obtain a Pt skin covering the PtREM alloy bulk, as was revealed by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The core shell alloys of Pt Y and Pt Gd catalysts show a specific activity enhancement at 0.9 V of 2.5 times compared to pure Pt. The slightly lower enhancement factor of 2.0 for Pt Tb is concluded to be due to leaching of the REM, that resulted in a thicker, and subsequently less strained, Pt overlayer. The high activity, combined with the minor changes in surface composition, achieved in the fuel cell environment shows that PtREM core shell catalysts are promising for the cathode reaction in PEMFC.
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| 6. |
- Lindahl, Niklas, 1981, et al.
(författare)
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Fuel Cell Measurements with Cathode Catalysts of Sputtered Pt3Y Thin Films
- 2018
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 11:9, s. 1438-1445
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Tidskriftsartikel (refereegranskat)abstract
- Fuel cells are foreseen to have an important role in sustainable energy systems, provided that catalysts with higher activity and stability are developed. In this study, highly active sputtered thin films of platinum alloyed with yttrium (Pt 3 Y) are deposited on commercial gas diffusion layers and their performance in a proton exchange membrane fuel cell is measured. After acid pretreatment, the alloy is found to have up to 2.5 times higher specific activity than pure platinum. The performance of Pt 3 Y is much higher than that of pure Pt, even if all of the alloying element was leached out from parts of the thin metal film on the porous support. This indicates that an even higher performance is expected if the structure of the Pt 3 Y catalyst or the support could be further improved. The results show that platinum alloyed with rare earth metals can be used as highly active cathode catalyst materials, and significantly reduce the amount of platinum needed, in real fuel cells.
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| 7. |
- Wickman, Björn, 1980, et al.
(författare)
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Modeling mass transport with microkinetics in monolithic NOx storage and reduction catalyst
- 2007
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 42-43:1-4, s. 123-127
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Tidskriftsartikel (refereegranskat)abstract
- A 2D axisymetric model of a NOx storage and reduction catalyst monolith channel combining mass transport with a detailed kinetic model was created to evaluate the importance of mass transport in a Pt/BaO/Al2O3 washcoat. Results show that there are small radial gradients in stored species concentration early during transients. The Sherwood number calculated during the transient storage phase will not be constant in time nor space as a film correlation would predict, but instead shows a region of higher Sherwood number propagating through the channel as the storage reaches completion. It is concluded that incorporating detailed mass transport provides a better spatially resolved picture of the dynamics of the proposed reaction mechanism and minimises the risk of arriving at false intrinsic kinetics during the development of a microkinetic model.
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| 8. |
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| 9. |
- Bengtsson, Mattias, 1994, et al.
(författare)
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Decontamination of Mercury-Containing Aqueous Streams by Electrochemical Alloy Formation on Copper
- 2019
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 58:21, s. 9166-9172
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Tidskriftsartikel (refereegranskat)abstract
- Mercury in aqueous streams poses severe health and environmental concerns and requires improved techniques for decontamination. One such technique is electrochemical alloy formation on platinum, which can effectively decontaminate mercury-containing aqueous streams at concentrations relevant for both industrial and natural waters. This study examines the viability of copper as an alternative to platinum. Mercury removal is faster on copper and works both with and without an applied cathodic potential. Without it, however, copper dissolution becomes a problem. Copper dissolution is preventable in neutral pH and in sulfuric acid solutions under potential control, and dissolved copper ions can be plated back onto the electrode. In the presence of nitrate or chloride anions, copper electrodes degrade rapidly even under potential control. Thus, there are practical restrictions for mercury decontamination via electrochemical alloy formation on copper, but it can be applied to solutions where copper is stable under potential control.
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| 10. |
- Bergmann, Michael Alexander, 1989, et al.
(författare)
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Electrochemical etching of AlGaN for the realization of thin-film devices
- 2019
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 115:18, s. 182103-
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Tidskriftsartikel (refereegranskat)abstract
- Heterogeneously integrated AlGaN epitaxial layers will be essential for future optical and electrical devices like thin-film flip-chip ultraviolet (UV) light-emitting diodes, UV vertical-cavity surface-emitting lasers, and high-electron mobility transistors on efficient heat sinks. Such AlGaN-membranes will also enable flexible and micromechanical devices. However, to develop a method to separate the AlGaN-device membranes from the substrate has proven to be challenging, in particular, for high-quality device materials, which require the use of a lattice-matched AlGaN sacrificial layer. We demonstrate an electrochemical etching method by which it is possible to achieve complete lateral etching of an AlGaN sacrificial layer with up to 50% Al-content. The influence of etching voltage and the Al-content of the sacrificial layer on the etching process is investigated. The etched N-polar surface shows the same macroscopic topography as that of the as-grown epitaxial structure, and the root-mean square roughness is 3.5 nm for 1 µm x 1 µm scan areas. Separated device layers have a well-defined thickness and smooth etched surfaces. Transferred multi-quantum-well structures were fabricated and investigated by time-resolved photoluminescence measurements. The quantum wells showed no sign of degradation caused by the thin-film process.
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| 11. |
- Bilesan, Mohammad Reza, et al.
(författare)
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Efficient separation of precious metals from computer waste printed circuit boards by hydrocyclone and dilution-gravity methods
- 2021
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Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526. ; 286
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Tidskriftsartikel (refereegranskat)abstract
- To fulfill the different aspects of green chemistry and to achieve full use of the secondary resources (waste printed circuit boards (WPCB)), the necessity of developing green methods for recovery of precious metals (Au, Pd, and Ag) is highly demanded. In this study, a novel environment-friendly physical separation approach; the combination of crushing, grinding, sieving as pretreatment steps alongside hydrocyclone and the dilution-gravity method (DGM) as the main final steps; is proposed. Inductively coupled plasma-mass spectrometry (ICP-MS), atomic absorption spectroscopy (AAS), and energy-dispersive X-ray spectroscopy (EDS) characterization methods were utilized to understand the effects of different separation steps applied in this research. The size and shape of grinded materials and the ones produced after hydrocyclone and DGM were evaluated using scanning electron microscopy. The results showed that the sieving step separated the highest gold fraction in the finer classification (<75 μm) while placed the copper (70 wt.%) into the coarser contents. The overflow to underflow outlet diameter ratio and inlet pressure was evaluated to determine the separation efficiency of a hydrocyclone effect of parameters. In the best-case scenario at 3 bar hydrocyclone operation pressure where the overflow to underflow outlet diameter (Do/Du) was 6.5, the highest metal fraction (87 wt.%) was achieved in the sink of the DGM. In this case, the total separation efficiency of gold, palladium, silver, and copper was 75%, 78%, 64%, 72%, respectively. Thus, this study demonstrates the feasibility of utilizing the sieving as mentioned above classification pretreatment steps followed by hydrocyclone and DGM methods as promising approaches for recovering precious metals from WPCBs that contain annually almost 50 million tons of e-waste.
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| 12. |
- Brown, Rosemary, 1990, et al.
(författare)
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Unraveling the Surface Chemistry and Structure in Highly Active Sputtered Pt3Y Catalyst Films for the Oxygen Reduction Reaction
- 2020
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 12:4, s. 4454-4462
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Tidskriftsartikel (refereegranskat)abstract
- Platinum is the most widely used and best performing sole element for catalyzing the oxygen reduction reaction (ORR) in low-temperature fuel cells. Although recyclable, there is a need to reduce the amount used in current fuel cells for their extensive uptake in society. Alloying platinum with rare-earth elements such as yttrium can provide an increase in activity of more than seven times, reducing the amount of platinum and the total amount of catalyst material required for the ORR. As yttrium is easily oxidized, exposure of the Pt-Y catalyst layer to air causes the formation of an oxide layer that can be removed during acid treatment, leaving behind a highly active pure platinum overlayer. This paper presents an investigation of the overlayer composition and quality of Pt3Y films sputtered from an alloy target. The Pt3Y catalyst surface is investigated using synchrotron radiation X-ray photoelectron spectroscopy before and after acid treatment. A new substoichiometric oxide component is identified. The oxide layer extends into the alloy surface, and although it is not completely removed with acid treatment, the catalyst still achieves the expected high ORR activity. Other surface-sensitive techniques show that the sputtered films are smooth and bulk X-ray diffraction reveals many defects and high microstrain. Nevertheless, sputtered Pt3Y exhibits a very high activity regardless of the film's oxide content and imperfections, highlighting Pt3Y as a promising catalyst. The obtained results will help to support its integration into fuel cell systems.
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| 13. |
- Ekström, Henrik, et al.
(författare)
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Nanometer-thick films of titanium oxide acting as electrolyte in the polymer electrolyte fuel cell
- 2007
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 52:12, s. 4239-4245
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Tidskriftsartikel (refereegranskat)abstract
- 0–18 nm-thick titanium, zirconium and tantalum oxide films are thermally evaporated on Nafion 117 membranes, and used as thin spacer electrolyte layers between the Nafion and a 3 nm Pt catalyst film. Electrochemical characterisation of the films in terms of oxygen reduction activity, high frequency impedance and cyclic voltammetry in nitrogen is performed in a fuel cell at 80 ◦C and full humidification. Titanium oxide films with thicknesses up to 18 nm are shown to conduct protons, whereas zirconium oxide and tantalum oxide block proton transport already at a thickness of 1.5 nm. The performance for oxygen reduction is higher for a bi-layered film of 3 nm platinum on 1.5 or 18 nm titanium oxide, than for a pure 3 nm platinum film with no spacer layer. The improvement in oxygen reduction performance is ascribed to a higher active surface area of platinum, i.e. no beneficial effect of combining platinum with zirconium, tantalum or titanium oxides on the intrinsic oxygen reduction activityis seen. The results suggest that TiO2 may be used as electrolyte in fuel cell electrodes, and that low-temperature proton exchange fuel cells could be possible using TiO2 as electrolyte.
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| 14. |
- Feldt, Emma, 1995, et al.
(författare)
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Temperature and concentration dependence of the electrochemical PtHg4 alloy formation for mercury decontamination
- 2023
-
Ingår i: Separation and Purification Technology. - 1873-3794 .- 1383-5866. ; 319
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Tidskriftsartikel (refereegranskat)abstract
- New and improved methods to remove toxic mercury from contaminated waters and waste streams are highly sought after. Recently, it was shown that electrochemical alloy formation of PtHg4 on a platinum surface with mercury ions from solution can be utilized for decontamination, with several advantages over conventional techniques. Herein, we examine the alloy formation process in more detail by mercury concentration measurements using inductively coupled plasma mass spectrometry in batch measurements as well as electrochemical quartz crystal microbalance analysis both in batch and in flowing water with initial mercury concentrations ranging from 0.25 to 75000 µg L−1 Hg2+. Results show that mercury is effectively removed from all solutions and the rate of alloy formation is constant over time, as well as for very thick layers of PtHg4. The apparent activation energy for the electrochemical alloy formation was determined to be 0.29 eV, with a reaction order in mercury ion concentration around 0.8. The obtained results give new insights that are vital in the assessment and further development of electrochemical alloy formation as a method for large scale mercury decontamination.
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| 15. |
- Frydendal, Rasmus, et al.
(författare)
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Benchmarking the Stability of Oxygen Evolution Reaction Catalysts: The Importance of Monitoring Mass Losses
- 2014
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Ingår i: ChemElectroChem. - : Wiley. - 2196-0216. ; 1:12, s. 2075-2081
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Tidskriftsartikel (refereegranskat)abstract
- Because of the rising need for energy storage, potentially facilitatedby electrolyzers, improvements to the catalysis of theoxygen evolution reaction (OER) become increasingly relevant.Standardized protocols have been developed for determiningcritical figures of merit, such as the electrochemical surfacearea, mass activity and specific activity. Even so, when new andmore active catalysts are reported, the catalyst stability tendsto play a minor role. In this work, we monitor corrosion onRuO2 and MnOx by combining the electrochemical quartz crystalmicrobalance (EQCM) with inductively coupled plasma massspectrometry (ICP–MS). We show that a meaningful estimationof the stability cannot be achieved based on purely electrochemicaltests. On the catalysts tested, the anodic dissolutioncurrent was four orders of magnitude lower than the total current.We propose that even if long-term testing cannot be replaced,a useful evaluation of the stability can be achievedwith short-term tests by using EQCM or ICP–MS.
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| 16. |
- Hellman, Anders, 1974, et al.
(författare)
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Electro-oxidation of water on hematite: Effects of surface termination and oxygen vacancies investigated by first-principles
- 2015
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 640, s. 45-49
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Tidskriftsartikel (refereegranskat)abstract
- The oxygen evolution reaction on hydroxyl- and oxygen-terminated hematite was investigated using first-principle calculations within a theoretical electrochemical framework. Both pristine hematite and hematite containing oxygen vacancies were considered. The onset potential was determined to be 1.79 V and 2.09 V vs. the reversible hydrogen electrode (RHE) for the pristine hydroxyl- and oxygen-terminated hematite, respectively. The presence of oxygen vacancies in the hematite surface resulted in pronounced shifts of the onset potential to 3.09 V and 1.83 V. respectively. Electrochemical oxidation measurements conducted on thin-film hematite anodes, resulted in a measured onset potential of 1.66 V vs. RHE. Furthermore, the threshold potential between the hydroxyl- and oxygen-terminated hematite was determined as a function of pH. The results indicate that electrochemical water oxidation on hematite occurs on the oxygen-terminated hematite, containing oxygen vacancies.
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| 17. |
- Helmer, Pernilla, et al.
(författare)
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Investigation of 2D Boridene from First Principles and Experiments
- 2022
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Recently, a 2D metal boride - boridene - has been experimentally realized in the form of single-layer molybdenum boride sheets with ordered metal vacancies, through selective etching of the nanolaminated 3D parent borides (Mo2/3Y1/3)(2)AlB2 and (Mo2/3Sc1/3)(2)AlB2. The chemical formula of the boridene was suggested to be Mo4/3B2-xTz, where T-z denotes surface terminations. Here, the termination composition and material properties of Mo4/3B2-xTz from both theoretical and experimental perspectives are investigated. Termination sites are considered theoretically for termination species T = O, OH, and F, and the energetically favored termination configuration is identified at z = 2 for both single species terminations and binary termination mixes of different stoichiometries in ordered and disordered configurations. Mo4/3B2-xTz is shown to be dynamically stable for multiple termination stoichiometries, displaying semiconducting, semimetallic, or metallic behavior depending on how different terminations are combined. The approximate chemical formula of a freestanding film of boridene is attained as Mo1.33B1.9O0.3(OH)(1.5)F-0.7 from X-ray photoelectron spectroscopy (XPS) analysis which, within error margins, is consistent with the theoretical results. Finally, metallic and additive-free Mo4/3B2-xTz shows high catalytic performance for the hydrogen evolution reaction, with an onset potential of 0.15 V versus the reversible hydrogen electrode.
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| 18. |
- Huerta-Flores, Ali M., et al.
(författare)
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Extended visible light harvesting and boosted charge carrier dynamics in heterostructured zirconate-FeS2 photocatalysts for efficient solar water splitting
- 2018
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Ingår i: Journal of Materials Science: Materials in Electronics. - : Springer Science and Business Media LLC. - 1573-482X .- 0957-4522. ; 29:22, s. 18957-18970
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Tidskriftsartikel (refereegranskat)abstract
- Limited visible light absorption, slow charge transference, and high recombination are some of the main problems associated with low efficiency in photocatalytic processes. For these reasons, in the present work, we develope novel zirconate-FeS2 heterostructured photocatalysts with improved visible light harvesting, effective charge separation and high photocatalytic water splitting performance. Herein, alkali and alkaline earth metal zirconates are prepared by a solid state reaction and coupled to FeS2 through a simple wet impregnation method. The incorporation of FeS2 particles induces visible light absorption and electron injection in zirconates, while the appropriate coupling of the semiconductors in the heterostructure allows an enhanced charge separation and suppression of the recombination. The obtained heterostructures exhibit high and stable photocatalytic activity for water splitting under visible light, showing competitive efficiencies among other reported materials. The highest hydrogen evolution rate (4490 mu molg(-1)h(-1)) is shown for BaZrO3-FeS2 and corresponds to more than 20 times the activity of the bare BaZrO3. In summary, this work proposes novel visible light active heterostructures for efficient visible light photocatalytic water splitting.
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| 19. |
- Huerta-Flores, Ali M., et al.
(författare)
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Green synthesis of earth-abundant metal sulfides (FeS2, CuS, and NiS2) and their use as visible-light active photocatalysts for H2 generation and dye removal
- 2018
-
Ingår i: Journal of Materials Science: Materials in Electronics. - : Springer Science and Business Media LLC. - 1573-482X .- 0957-4522. ; 29:13, s. 11613-11626
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Tidskriftsartikel (refereegranskat)abstract
- Earth-abundant metal sulfides (for example, FeS2, CuS, and NiS2) are promising materials to be used as photocatalysts due to their suitable electronic and optical properties. In this work, we present a fast and low-cost hydrothermal method to synthesize these materials. They are integrally characterized and evaluated as photocatalysts for the H2evolution reaction and the degradation of indigo carmine (IC). FeS2exhibits the highest photocatalytic efficiency (32 µmol g−1 h−1of H2evolution and 88% of indigo carmine degradation) under visible light, and this activity is attributed to a larger crystallite size, smaller particle size, and lower recombination, compared to CuS and NiS2. Moreover, three different sacrificial reagents are studied for the H2evolution reaction, including Na2S/Na2SO3, EDTA, and ethanol. Na2S/Na2SO3shows the highest enhancement in the activity, increasing the rate of H2production more than 15 times. This behavior is related to the lower oxidation potential of Na2S/Na2SO3. Moreover, we evaluate the activity of the materials for the electrochemical hydrogen evolution reaction (HER). In summary, this work provides valuable information for effective applications of these earth-abundant metal sulfides for energy and environmental photocatalytic processes.
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| 20. |
- Iandolo, Beniamino, 1985, et al.
(författare)
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Correlating flat band and onset potentials for solar water splitting on model hematite photoanodes
- 2015
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 5:75, s. 61021-61030
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Tidskriftsartikel (refereegranskat)abstract
- Hematite (α-Fe2O3) is a very promising material for solar water splitting that requires a high anodic potential to initiate the oxygen evolution reaction (OER). In this work, we explore the correlation between the downshift in flat band potential of hematite, Vfb, and in onset potential of OER, Vonset, caused by prolonged annealing. We observed a cathodic shift (i.e., towards lower potentials) of 200 mV of Vonset on model photoanodes consisting of ultra-thin hematite films, upon increasing the oxidation time during fabrication and without any further modifications. Detailed physical characterization, electrochemical impedance spectroscopy, and Mott-Schottky analysis revealed a quantitative correlation between the cathodic shift of Vonset and a lowering of Vfb. We identified a reduction in concentration of grain boundaries with increasing oxidation time, as the mechanism behind the observed shift of the Vfb. The approach presented here can be seen as a complementary strategy to co-catalysts and other post-fabrication treatments to lower Vonset. Moreover, it is generically applicable to photoelectrodes used to carry out oxidation and reduction half-cell reactions.
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| 21. |
- Iandolo, Beniamino, 1985, et al.
(författare)
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Faradaic efficiency of O-2 evolution on metal nanoparticle sensitized hematite photoanodes
- 2014
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 16:3, s. 1271-1275
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Tidskriftsartikel (refereegranskat)abstract
- Functionalization of transition metal oxides using metallic nanoparticles is an interesting route towards efficient photoelectrochemical hydrogen production via water splitting. Although an enhanced photocurrent in photoanodes upon functionalization with metallic nanostructures has been observed in several studies, to the best of our knowledge no measurements of the Faradaic efficiency (FE) of the oxygen evolution reaction (OER) have been reported for such systems. This work characterizes the FE on a model system consisting of ultra-thin films of hematite (Fe2O3) sensitized with Ti/Au nanodisks. Compared to bare hematite references, sensitized samples showed significantly enhanced photocurrents as well as O-2 evolution. Experimental evidence suggests that the observed enhancement was not due to photocatalytic activity of the nanodisks. The FE has been determined to be 100%, within the experimental errors, for both sensitized and reference samples. Also, this work demonstrates that the sensitized samples were stable for at least 16 hours photocurrent testing. The concepts shown in this work are generally applicable to any situation in which a semiconductor has its water splitting performance enhanced by metallic nanostructures.
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| 22. |
- Iandolo, Beniamino, 1985, et al.
(författare)
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Tailoring Charge Recombination in Photoelectrodes Using Oxide Nanostructures
- 2016
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 16:4, s. 2381-2386
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Tidskriftsartikel (refereegranskat)abstract
- Optimizing semiconductor devices for solar energy conversion requires an explicit control of the recombination of photogenerated electron hole pairs. Here we show how the recombination of charge carriers can be controlled in semiconductor thin films by surface patterning with oxide nanodisks. The control mechanism relies on the formation of dipole-like electric fields at the interface that, depending on the field direction, attract or repel minority carriers from underneath the disks. The charge recombination rate can be controlled through the choice of oxide material and the surface coverage of nanodisks. We provide proof-of-principle demonstration of this approach by patterning the surface of Fe2O3, one of the most studied semiconductors for light-driven water splitting, with TiO2 and Cu2O nanodisks. We expect this method to be generally applicable to a range of semiconductor-based solar energy conversion devices.
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| 23. |
- Iandolo, Beniamino, 1985, et al.
(författare)
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The rise of hematite: origin and strategies to reduce the high onset potential for the oxygen evolution reaction
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:33, s. 16896-16912
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Tidskriftsartikel (refereegranskat)abstract
- Hematite (alpha-Fe2O3) has emerged as a promising material for photoelectrochemical (PEC) water splitting thanks to its abundance, stability in an aqueous environment, favorable optical bandgap and position of the electronic valence band. Nevertheless, its performance as a photoanode is considerably lower than what is theoretically achievable. In particular, the high electrochemical potential usually needed to initiate water oxidation is detrimental to the prospect of using hematite for practical devices. In this review we elucidate the appealing, as well as the challenging, aspects of using hematite for PEC water splitting and focus on the recent efforts towards lowering the onset potential of water oxidation. We examine and rationalize several strategies pursued to achieve this goal involving manipulation of the hematite/electrolyte interface, as well as improving relevant properties of hematite itself.
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| 24. |
- JOHANSSON, DAVID, et al.
(författare)
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Nanoplasmonic sensing of Pb-acid and Li-ion batteries
- 2016
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Ingår i: Presented at the 2nd International Conference on Sensors and Electronic Instrumental Advances (SEIA), Barcelona, Spain, September 22 – 23, 2016. - : INT FREQUENCY SENSOR ASSOC-IFSA. ; , s. 57-59, s. 57-59
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Konferensbidrag (refereegranskat)abstract
- The increasing sophistication and performance of batteries are connected with more complex chemical and physical battery processes and increase the need of more direct and informative measurements, both in the R&D phase and for monitoring and control during operation of vehicles. Todays potentiometric based measurement sensors are not sufficiently accurate for optimal battery sensing. To avoid the built in wide safety margins new, more informative monitoring signals are therefore desired or needed. In this study the optical technology NanoPlasmonic Sensing (NPS) has been used to in-situ monitor the charge and discharge processes of lead-acid and Li-ion batteries. The optical signals were found to correlate well with charging/discharging of both battery technologies.
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| 25. |
- Kodan, Nisha, et al.
(författare)
-
Favourable band edge alignment and increased visible light absorption in β-MoO3/α-MoO3 oxide heterojunction for enhanced photoelectrochemical performance
- 2018
-
Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 43:33, s. 15773-15783
-
Tidskriftsartikel (refereegranskat)abstract
- Optimum band gap values, favourable band edge positions and stability in the electrolyte are critical parameters required for a semiconductor to have efficient photoelectrode properties. The present investigation carried out on the phase pure α & β MoO3 thin film shows that the low bandgap β-MoO3 possesses a mis-alignment with the water oxidation potential, while a more suitable band alignment is observed for the comparatively large bandgap α-MoO3. Both experimental and DFT calculations show that the valence edge of the orthorhombic (α-MoO3) phase is located at a higher energy (0.9 eV higher in VB-XPS and 1 eV higher in the DOS plots) than the monoclinic (β-MoO3) phase, while the conduction edge value is roughly at the same energy level (−2.5 eV) in both polymorphs. Based on the above investigations, an all oxide heterojunction comprising of β-MoO3/α-MoO3 is found to be suitable for improved PEC performance due to favourable energy band diagram and increased visible light absorption in β-MoO3. Significantly higher cathodic photocurrent is observed for the β-MoO3/α-MoO3 (1.6 mA/cm2 at applied bias of −0.3VRHE under simulated 1 sun irradiation) as compared to the very low anodic response in β-MoO3 (∼1.0 nA/cm2) and α-MoO3 (32 μA/cm2).
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| 26. |
- Kudra, Marina, 1992, et al.
(författare)
-
High quality three-dimensional aluminum microwave cavities
- 2020
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 117:7
-
Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive study of internal quality factors in superconducting stub-geometry three-dimensional cavities made of aluminum. We use wet etching, annealing, and electrochemical polishing to improve the as machined quality factor. We find that the dominant loss channel is split between the two-level system loss and an unknown source with a 40:60 proportion. A total of 17 cavities of different purity, resonance frequency, and size were studied. Our treatment results in reproducible cavities, with 10 of them showing internal quality factors above 80 x 10(6) at a power corresponding to an average of a single photon in the cavity. The best cavity has an internal quality factor of 115 x 10(6) at a single photon level. (C) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http:// creativecommons.org/licenses/by/4.0/).
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| 27. |
- Kumar, S., et al.
(författare)
-
Dominant {100} facet selectivity for enhanced photocatalytic activity of NaNbO3 in NaNbO3/CdS core/shell heterostructures
- 2017
-
Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:2, s. 481-495
-
Tidskriftsartikel (refereegranskat)abstract
- Design and engineering of crystalline advanced photocatalysts with specific facets is one of the most challenging tasks to enhance the photocatalytic performance. The surface energy of different facets is different in a crystal which leads to a corresponding change in their photocatalytic behaviour. The present study provides an experimental as well as theoretical understanding of the role of different facets of NaNbO3 in cubic and orthorhombic phases with crystals showing cubic and cuboctahedron morphologies in enhancing the photocatalytic activity of NaNbO3/CdS core/shell heterostructures. Herein, we discuss the importance of the approach of facet-selective synthesis and trace the origin of enhanced photoelectrochemical (PEC) water splitting and photocatalytic dye degradation activity for calculated surface energies of the {100} family of facets of the cubic phase and the (110) and (114) facets of the orthorhombic phase of NaNbO3. We propose that different mechanisms contribute to the enhancement of catalytic activity in these two phases. In the prepared core/shell heterostructures containing NaNbO3 as the core material, the presence of highly reactive facets of the cubic phase contributes to higher photocatalytic activity as compared to the orthorhombic phase which has a spatial charge separation assisted inter-facet charge transfer mechanism.
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| 28. |
- Li, Guoqiang, et al.
(författare)
-
Activity of Platinum/Carbon and Palladium/Carbon Catalysts Promoted by Ni2P in Direct Ethanol Fuel Cells
- 2014
-
Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 7:12, s. 3374-3381
-
Tidskriftsartikel (refereegranskat)abstract
- Ethanol is an alternative fuel for direct alcohol fuel cells, inwhich the electrode materials are commonly based on Pt orPd. Owing to the excellent promotion effect of Ni2P that wasfound in methanol oxidation, we extended the catalyst systemof Pt or Pd modified by Ni2P in direct ethanol fuel cells. TheNi2P-promoted catalysts were compared to commercial catalystsas well as to reference catalysts promoted with only Ni oronly P. Among the studied catalysts, Pt/C and Pd/C modifiedby Ni2P (30 wt%) showed both the highest activity and stability.Upon integration into the anode of a homemade direct ethanolfuel cell, the Pt-Ni2P/C-30% catalyst showed a maximumpower density of 21 mWcm-2, which is approximately twotimes higher than that of a commercial Pt/C catalyst. The Pd-Ni2P/C-30% catalyst exhibited a maximum power density of90 mWcm-2. This is approximately 1.5 times higher than thatof a commercial Pd/C catalyst. The discharge stability on bothtwo catalysts was also greatly improved over a 12 h dischargeoperation.
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| 29. |
- Li, Zhuofeng, 1991-, et al.
(författare)
-
Tuning morphology, composition and oxygen reduction reaction (ORR) catalytic performance of manganese oxide particles fabricated by γ-radiation induced synthesis
- 2021
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 583, s. 71-79
-
Tidskriftsartikel (refereegranskat)abstract
- A γ-radiation induced synthesis method is used to fabricate manganese oxide catalysts through both reduction and oxidation routes. It is shown that the morphology, composition and electrochemical performance of the produced manganese oxide particles can be tuned by altering the redox conditions. The catalysts prepared via radiolytic oxidation have a hollow spherical morphology, possess γ-MnO2 structure and show high catalytic activity for the complete four-electron reaction pathway of the oxygen reduction reaction (ORR) in alkaline electrolyte. Meanwhile, the catalysts synthesized via radiolytic reduction possess a rod-like morphology with a Mn3O4 bulk structure and favour the incomplete two-electron reaction pathway for ORR. The high catalytic activity of the manganese oxide synthesized via the oxidation route can be attributed to high electrochemical surface area and increased amount of Mn3+ on the surface as compared to those in the sample obtained via the reduction route.
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| 30. |
- Lind, Hans, et al.
(författare)
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Hydrogen Evolution Reaction for Vacancy-Ordered i-MXenes and the Impact of Proton Absorption into the Vacancies
- 2021
-
Ingår i: Advanced Sustainable Systems. - : Wiley. - 2366-7486. ; 5:2
-
Tidskriftsartikel (refereegranskat)abstract
- A study of the hydrogen evolution reaction (HER) for Mo-, W-, and Nb-based MXenes is presented, where W1.33C MXene with ordered vacancies is chosen for further investigation. The electrochemical measurements show that if the W1.33C MXene is subjected to high cathodic potentials, it greatly improves the activity and onset potential for the HER. The enhancement continues to improve independent of whether the potential is kept fixed at a certain cathodic potential or if the potential is scanned repeatedly. Interestingly, the improvement disappears if the material is subjected to anodic potential. Based on these observations, the hydrogen interaction with the MXene surface as well as in the vacancies is investigated by means of first-principles calculations. These show that the adsorption energy of hydrogen is sensitive to both surface coverage and vacancy occupancy, and that, for certain structures with hydrogen in the vacancies, thermoneutral values of hydrogen adsorption can be obtained. Based on the calculations it is argued that under high cathodic potentials, protons can transfer to the vacancies and stay there in a metastable state as hydrogen atoms, while at anodic potential the process is reversed. The first-principles results provide a rationale for the strongly enhanced HER activity observed experimentally on W1.33C MXene.
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| 31. |
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| 32. |
- Lindahl, Niklas, 1981, et al.
(författare)
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High Specific and Mass Activity for the Oxygen Reduction Reaction for Thin Film Catalysts of Sputtered Pt3Y
- 2017
-
Ingår i: Advanced Materials Interfaces. - : Wiley. - 2196-7350. ; 4:13
-
Tidskriftsartikel (refereegranskat)abstract
- Fuel cells have the potential to play an important role in sustainable energy systems, provided that catalysts with higher activity and stability are developed. In this work, it is found that thin alloy films of single-target cosputtered platinum-yttrium exhibit up to seven times higher specific activity (13.4 +/- 0.4 mA cm(-2)) for the oxygen reduction reaction (ORR) than poly-crystalline platinum, and up to one order of magnitude higher mass activity (3.5 +/- 0.3 A mg(-1)) than platinum nanoparticles. These alloys have the highest reported ORR activity for an as-deposited material, i.e., without any additional chemical or thermal treatment. The films show an improvement in stability over the same materials in nanoparticulate form. Physical characterization shows that the thin films form a platinum overlayer supported on an underlying alloy. The high activity is likely related to compressive strain in that overlayer. As sputtering can be used to mass-produce fuel cell electrodes, the results open new possibilities for the preparation of platinum-rare earth metal alloy catalysts in commercial devices.
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| 33. |
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| 34. |
- Lindberg, Jonas, et al.
(författare)
-
The effect of O2 concentration on the reaction mechanism in Li-O2 batteries
- 2017
-
Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657 .- 0022-0728 .- 1873-2569. ; 797, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- The promising lithium-oxygen battery chemistry presents a set of challenges that need to be solved if commercialization is ever to be realized. This study focuses on how the O2 reaction path is effected by the O2 concentration in the electrolyte. An electrochemical quartz crystal microbalance system was used to measure current, potential, and change in electrode mass simultaneously. It is concluded that the mass reversibility is O2 concentration dependent while the coulombic efficiency is not. The mass reversibility is higher at low O2 concentration meaning that more of the deposited Li2O2 is removed during oxidation in relation to the amount deposited during reduction. The first step of the reduction is the formation of soluble LiO2, which is then either reacting further at the electrode or being transported away from the electrode resulting in low current efficiency and low deposited mass per electrons transferred. During the oxidation, the first step involves de-lithiation of Li2O2 at low potential followed by bulk oxidation. The oxidation behavior is O2 concentration dependent, and this dependence is likely indirect as the O2 concentration effects the amount of discharge product formed during the reduction. The O2 concentration at different saturation pressures was determined using a mass spectrometer. It was found that the electrolyte follows Henry's law at the pressures used in the study. In conclusion, this study provides insight to the O2 concentration dependence and the preferred path of the O2 electrochemical reactions in lithium-oxygen batteries.
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| 35. |
- Luneau, Mathilde, 1989, et al.
(författare)
-
Fundamental insight into enhanced activity of Pd/CeO 2 thin films in hydrogen oxidation reaction in alkaline media
- 2023
-
Ingår i: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 11:30, s. 16370-16382
-
Tidskriftsartikel (refereegranskat)abstract
- Palladium supported on ceria (Pd/CeO2) has recently raised strong interest as an alternative catalyst to platinum on the anode electrode in anion exchange membrane fuel cells. Herein, we provide new insight into the enhanced activity of Pd/CeO2 in hydrogen oxidation reaction (HOR) in alkaline media. Using well-defined model thin films, we show that Pd/CeO2 thin films lead to enhanced activity in HOR compared to pure Pd thin films. In situ characterization using electrochemical quartz crystal microbalance provide in-depth understanding of the role of CeO2. CeO2 leads to fundamental differences in adsorption and absorption of key reaction intermediates during HOR. In combination with characterization and theoretical calculations, Pd atoms embedded in CeO2 are shown to be present on the prepared thin films and active for hydrogen activation but are not able to bind CO during CO-stripping characterization. Finally, an estimation of the source of hydroxyl intermediates provided by CeO2 - which could be directly participating in the reaction - is presented herein. Fundamental understanding of the Pd-CeO2 interface in HOR opens new ways to reduce the amount of noble metals in alkaline fuel cells.
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| 36. |
- Marra, Eva, et al.
(författare)
-
Oxygen reduction reaction kinetics on a Pt thin layer electrode in AEMFC
- 2022
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 435, s. 141376-141376
-
Tidskriftsartikel (refereegranskat)abstract
- The study of the catalytic activity in a fuel cell is challenging, as mass transport, gas crossover and the counterelectrode are generally interfering. In this study, a Pt electrode consisting of a thin film deposited on the gasdiffusion layer was employed to study the oxygen reduction reaction (ORR) in an operating Anion Exchange Membrane Fuel Cell (AEMFC). The 2D Pt electrode was assembled together with a conventional porous Pt/Ccounter electrode and an extra Pt/C layer and membrane to reduce the H2 crossover. Polarization curves atdifferent O2 partial pressures were recorded and the resulting reproducible ORR activities were normalized withrespect to the active surface area (ECSA), obtained by CO stripping. As expected, decreasing the O2 partialpressure results in a negative shift in open circuit voltage (OCV), cell voltage and maximum attainable currentdensity. For cell voltages above 0.8 V a fairly constant Tafel slope of 60 mV dec−1 was recorded but at lowervoltages the slope increases rapidly. The observed Tafel slope can be explained by a theoretical model with anassociative mechanism where charge- and proton-transfer steps are decoupled, and the proton transfer is the rate-determining step. A reaction order of 1 with respect to O2 was obtained at 0.65 V which corresponds well withthe mechanism suggested above. Based on the obtained catalyst activities, the electrode performance is comparable to good porous electrodes found in the field. The methodology presented in this study is expected to beuseful in future kinetic studies of other catalysts for AEMFC.
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| 37. |
- Mehta, Manan, et al.
(författare)
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Synthesis of MoS2-TiO2 nanocomposite for enhanced photocatalytic and photoelectrochemical performance under visible light irradiation
- 2018
-
Ingår i: Vacuum. - : Elsevier BV. - 0042-207X. ; 155, s. 675-681
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we have prepared MoS2 nanoflakes modified TiO2 nanoparticles (MoS2-TiO2 nanocomposite) with varying concentration of MoS2 (2.5–10 wt.%) by a two-step hydrothermal synthesis method involving specific preparation conditions for the TiO2 nanoparticles and MoS2 nanoflakes. The prepared samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS) techniques. The photocatalytic activity of the pristine TiO2 nanoparticles and MoS2-TiO2 nanocomposite samples were evaluated by examining the photocatalytic degradation of Rhodamine B (RhB). The photoelectrochemical activity of these samples were measured by performing solar water splitting experiments under visible light irradiation. It was observed that the MoS2-TiO2 nanocomposite with 7.5 wt.% MoS2 exhibits highest photocatalytic and photoelectrochemical activity as it has the optimum amount of MoS2 nanoflakes which probably minimizes the recombination of photogenerated charge carriers as compared to other concentrations of MoS2 in MoS2-TiO2 nanocomposite and pristine TiO2 nanoparticles. In addition, a rather high photocatalytic reaction rate constant was observed for MoS2-TiO2 nanocomposite with 7.5 wt.% MoS2 nanoflakes.
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| 38. |
- Meshkian, Rahele, et al.
(författare)
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W-Based Atomic Laminates and Their 2D Derivative W1.33C MXene with Vacancy Ordering
- 2018
-
Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 30:21
-
Tidskriftsartikel (refereegranskat)abstract
- Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i-MAX phases with in-plane chemical order and a general chemistry (W 2/3 M 2 1/3 ) 2 AC, where M 2 = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only two—with a monoclinic C2/c structure—are predicted to be stable: (W 2/3 Sc 1/3 ) 2 AlC and (W 2/3 Y 1/3 ) 2 AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W 1.33 C-based MXene sheets with ordered metal divacancies. Using electrochemical experiments, this MXene is shown to be a new, promising catalyst for the hydrogen evolution reaction. The addition of yet one more element, W, to the stable of M elements known to form MAX phases, and the synthesis of a pure W-based MXene establishes that the etching of i-MAX phases is a fruitful path for creating new MXene chemistries that has hitherto been not possible, a fact that perforce increases the potential of tuning MXene properties for myriad applications.
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| 39. |
- Montserrat Siso, Gerard, 1992, et al.
(författare)
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PdNi thin films for hydrogen oxidation reaction and oxygen reduction reaction in alkaline media
- 2022
-
Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 420
-
Tidskriftsartikel (refereegranskat)abstract
- Pd-based catalysts are considered to be among the most promising electrocatalysts for both the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) in alkaline media. Although major progress in finding effective catalysts has been made, the reasons for the activity enhancement in alkaline conditions remain to be elucidated. Herein, we report the fabrication of alloyed PdNi thin films as a tool to study the HOR and ORR reactions. Annealing of physically evaporated PdNi thin films at different temperatures results in different surface compositions and a range of HOR and ORR activities in 0.1 M KOH. Moreover, annealed samples were acid treated to remove the surface Ni and the HOR and ORR were investigated to elucidate the effect of surface and subsurface Ni. For the HOR, it was found that the addition of Ni decreases the hydrogen binding energy (HBE) of Pd through an electronic effect, which results in an increase in activity. In addition, it was found that the HOR activity was further increased by the bifunctional effect induced by surface Ni, which provides OH− adsorption sites. In contrast to HOR, it was concluded that surface Ni was disadvantageous for the ORR. However, subsurface Ni was found to induce an electronic effect on Pd that resulted in a somewhat improvement of the ORR kinetics by improving its oxygen desorption. These results provide insights for more tailored design of electrocatalysts in alkaline media by shedding new light on the mechanisms through which the HOR and ORR kinetics are improved in alkaline media.
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| 40. |
- Montserrat Siso, Gerard, 1992, et al.
(författare)
-
Tuning the Activity of Silver Alloys for the Oxygen Reduction Reaction in Alkaline Media
- 2023
-
Ingår i: ACS Applied Energy Materials. - 2574-0962. ; 6:12, s. 6428-6442
-
Tidskriftsartikel (refereegranskat)abstract
- Ag-based catalysts have recently attracted much attentionas potentialcandidates to substitute costly Pt-based electrocatalysts for theoxygen reduction reaction (ORR) in alkaline media. Although the electrocatalyticactivity of Pt-based alloys is known to exhibit a strong dependenceon their electronic structures, a relationship between electronicstructure and the ORR mechanism in Ag-based alloys still remains tobe elucidated. Herein, by means of physical vapor deposition, we prepareAg binary thin films (CoAg, CuAg, AuAg, and FeAg) with well-controlledcompositions as a tool to investigate the ORR mechanism on Ag surfaces.The bimetallic thin films are evaluated for their ORR performancein alkaline media, and their specific activity at 0.8 V-RHE is shown to correlate with the Ag electronic structure. Even thoughall thin films show different responses to potential cycling, allbimetallic samples exhibit a surface Ag enrichment after ORR. It isshown that the ORR occurs through different mechanisms on these Ag-richsurfaces, which in turn is potential-dependent. Tafel slopes revealfaster ORR kinetics at low overpotentials on all surfaces, whereasonly CuAg surpasses pure Ag at higher overpotentials. Moreover, despitetheir incomplete O-2 reduction, CuAg and AuAg exhibit anoverall superior ORR activity over pure Ag, with a more than 2-foldincrease in specific activity at 0.8 V-RHE attributed toenhancements originating from electronic effects and surface defects,respectively. Since the potential-dependent improved ORR mechanismobserved for Ag bimetallic samples makes a rational design of Ag-basedelectrocatalysts difficult, these results aim to provide insightsfor a more tailored design of electrocatalysts by shedding light onthe mechanisms through which the ORR kinetics are improved on Ag surfacesin alkaline media.
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| 41. |
- Poliakov, Aleksandr, 1990, et al.
(författare)
-
Top-down nanostructured multilayer MoS2 with atomically sharp edges for electrochemical hydrogen evolution reaction
- 2024
-
Ingår i: Materials Today Nano. - 2588-8420. ; 25
-
Tidskriftsartikel (refereegranskat)abstract
- Cost-efficient and readily scalable platinum-free electrocatalysts are crucial for a smooth transition to future renewable energy systems. Top-down activation of MoS2 promises the production of sustainable hydrogen evolution electrocatalysts from the Earth-abundant molybdenite ore. Here, the deterministic nanopatterning of multilayer MoS2 with numerous zigzag edges is explored as a pathway to enhance hydrogen evolution reaction (HER). Nanopatterned single-nanosheet MoS2 electrodes are assessed by two highly localized electrochemical techniques: selected area voltammetry (with lithography-defined regions of electrode-electrolyte contact) and Scanning ElectroChemical Microscopy (SECM). The nanopatterning effect is the most pronounced after prolonged electrochemical cycling in an acidic electrolyte. The electrocatalytic hydrogen evolution activity of edge-enriched electrodes is dramatically enhanced: the maximum electrochemical current density (j) achieved at -510 mV vs. reversible hydrogen electrode (mV) is increased by two orders of magnitude, reaching >300 mA⋅cm−2. Both the and overpotentials are significantly reduced as well. Meanwhile, pristine MoS2 shows just ≈6 times j increase (≈30 mA⋅cm−2) after the very same cycling. The increased electrocatalytic activity comes with electrode morphology degradation, evidenced by ex-situ scanning electron microscopy. SECM directly visualizes stronger HER activity in the regions with densely located zigzag edges. Intense white light illumination significantly boosts HER on MoS2 electrodes due to the photo-enhanced MoS2 conductivity. These results improve the understanding and reveal the limitations of MoS2-based electrocatalytic water splitting.
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| 42. |
- Reza Bilesan, Mohammad, et al.
(författare)
-
Electrochemical Approach for Advanced Flow Reactors via Additive Manufacturing of High Surface Area Ti-6Al-4V Anode
- 2023
-
Ingår i: ChemElectroChem. - 2196-0216. ; 10:20
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochemical processes use expensive noble metal-based anodes which limit industrial implementation. In this study, a noble-metal-free Ti-6Al-4V anode is introduced in an advanced flow reactor. We demonstrate that the 3D additively manufactured electrode can provide a more projected surface area and facilitate anodic reactions under controlled electrolyte conditions. Alkaline NaOH and KOH electrolytes act as anodic electrolytes that are toxic compounds-free and enable corrosion control. Impedance and voltammetry responses to electrochemical reactions are studied. The electrochemical active surface area of the 4 rods scaffold geometry is 42 times higher than a flat plate anode. Therefore, improved charge transfer is achieved in the flow reactor incorporating the 3D Ti-6Al-4V electrode due to the increased surface area and wettability. The structure of almost non-conductive passivation on a flat plate anode is changed to unstable passivation due to the 3D scaffold structure. This enables effective charge transfer of 911 mA cm−2 at higher potentials up to 5 V for 1.5 m KOH in a non-flow condition. Furthermore, a 1 m KOH solution delays metal ion dissolution from the anode surface by acting as a corrosion-controlling medium. 3D Ti-6Al-4V is likely to be an affordable alternative anode in alkaline environmentally friendly electrochemical applications.
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| 43. |
- Roth, Vera, 1994, et al.
(författare)
-
Mercury Removal from Concentrated Sulfuric Acid by Electrochemical Alloy Formation on Platinum
- 2023
-
Ingår i: ACS ES and T Engineering. ; 3:6, s. 823-830
-
Tidskriftsartikel (refereegranskat)abstract
- Mercury is a highly toxic heavy metal, and improved removal processes are required in a range of industrial applications to limit the environmental impacts. At present, no viable removal methods exist commercially for mercury removal of aqueous solutions at high acidic conditions, such as concentrated sulfuric acid. Herein, we show that electrochemical mercury removal based on electrochemical alloy formation on platinum, forming PtHg4, can be used to remove mercury from concentrated sulfuric acid. Thin platinum film electrodes and porous electrodes with supported platinum are used to remove more than 90% of mercury from concentrated acid from a zinc smelter with an initial mercury concentration of 0.3-0.9 mg/kg, achieving high-quality acid (<0.08 mg/kg) within 80 h. The removal process is carried out in 50 mL laboratory-scale experiments and scaled up to a 20 L pilot reactor with retained removal efficiency, highlighting excellent scalability of the method. In addition, the removal efficiency and stability of different electrode substrate materials are studied to ensure high-quality acid and a long lifetime of the electrodes in harsh chemical conditions, offering a potential method for future large-scale mercury decontamination of sulfuric acid.
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| 44. |
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| 45. |
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| 46. |
- Seidel, Y.E., et al.
(författare)
-
Mesoscopic mass transport effects in electrocatalytic processes
- 2008
-
Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 140, s. 167-184
-
Tidskriftsartikel (refereegranskat)abstract
- The role of mesoscopic mass transport and re-adsorption effects in electrocatalytic reactions was investigated using the oxygen reduction reaction (ORR) as an example. The electrochemical measurements were performed on structurally well-defined nanostructured model electrodes under controlled transport conditions in a thin-layer flow cell. The electrodes consist of arrays of Pt ultra-microelectrodes (nanodisks) of defined size (diameter similar to 100 nm) separated on a planar glassy carbon (GC) substrate, which were fabricated employing hole-mask colloidal lithography (HCL). The measurements reveal a distinct variation in the ORR selectivity with Pt nanodisk density and with increasing electrolyte flow, showing a pronounced increase of the H2O2 yield, by up to 65%, when increasing the flow rate from 1 to 30 mu L s(-1). These results are compared with previous findings and discussed in terms of a reaction model proposed recently (A. Schneider et al., Phys. Chem. Chem. Phys., 2008, 10, 1931), which includes (i) direct reduction to H2O on the Pt surface and (ii) additional H2O2 formation and desorption on both Pt and carbon surfaces and subsequent partial re-adsorption and further reduction of the H2O2 molecules on the Pt surface. The potential of model studies on structurally defined catalyst surfaces and under well-defined mass transport conditions in combination with simulations for the description of electrocatalytic reactions is discussed.
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| 47. |
- Seidel, Y.E., et al.
(författare)
-
Mesoscopic transport effects in electrocatalytic reactions
- 2009
-
Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781566777902 ; 25:23, s. 91-102
-
Konferensbidrag (refereegranskat)abstract
- Transport effects may not only influence the rate of electrocatalytic reactions, but also the product distribution. The underlying effects were studied under well-defined reaction and transport conditions, using nanostructured Pt/glassy carbon electrodes, which consist of ordered arrays of electrocatalytically active Pt nanostructures on a planar glassy carbon substrate. The effect of varying the density of the Pt nanostructures or the electrolyte flow rate on the reaction characteristics and product distribution was investigated for apparently simple electrocatalytic reactions such as CO oxidation, methanol oxidation and oxygen reduction. It is shown that reducing the Pt coverage leads to an increase of the relative amount of the reaction intermediates. Similar effects are obtained for increasing the electrolyte flow rate. The results are discussed on a molecular scale in terms of the 'desorption - re-adsorption - reaction' model which we had introduced recently.
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| 48. |
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| 49. |
- Seidel, Y.E., et al.
(författare)
-
Transport effects in the electrooxidation of methanol studied on nanostructured Pt/glassy carbon electrodes
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 26:5, s. 3569-3578
-
Tidskriftsartikel (refereegranskat)abstract
- Transport effects in the methanol oxidation reaction (MOR) were investigated using nanostructured Pt/glassy carbon (GC) electrodes and, for comparison, a polycrystalline Pt electrode. The nanostructured Pt/GC electrodes, consisting of a regular array of catalytically active cylindrical Pt nanostructures with 55 +/- 10 nm in diameter and different densities supported on a planar GC substrate, were fabricated employing hole-mask colloidal lithography (HCL). The MOR measurements were performed under controlled transport conditions in a thin-layer flow cell interfaced to a differential electrochemical mass spectrometry (DEMS) setup. The measurements reveal a distinct variation in the MOR activity and selectivity (product distribution) with Pt nanostructure density and with electrolyte rate, showing an increasing overall activity, reflected by a higher Faradaic reaction current, as well as a pronounced increase of the turnover frequency for CO(2) formation and of the CO(2) current efficiency with decreasing flow rate and increasing Pt coverage. These findings are discussed in terms of the "desorption-readorption-reaction" model introduced recently (Seidel et al. Faraday Discuss 2008, 140, 67). Finally, consequences for applications in direct methanol fuel cells are outlined.
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| 50. |
- Shokhen, Victor, 1988, et al.
(författare)
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Fuel cell electrode degradation followed by identical location transmission electron microscopy
- 2023
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Ingår i: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 11:39, s. 21029-21035
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Tidskriftsartikel (refereegranskat)abstract
- Identical location transmission electron microscopy (IL-TEM) is a powerful technique that has previously been used to study degradation of catalyst materials for proton exchange membrane fuel cells (PEMFCs) in half-cell environments. Here, we demonstrate that IL-TEM can be used to follow degradation at the top of the catalytic Pt/C layer in a real PEMFC on the atomic scale under operation. We find that during an accelerated stress test (AST), mimicking normal operation, Pt nanoparticles grow mainly by Ostwald ripening, while the carbon support is stable. Under AST mimicking start-up/shutdown conditions, the carbon support degrades mainly by loss of volume and collapse, which forces the Pt nanoparticles closer, promoting additional particle growth. The observed degradation correlates with the measured decrease in electrochemical performance for the respective AST. The results show the feasibility of performing IL-TEM imaging in PEMFCs under real-operating conditions, opening up the possibility for similar studies in other fully operational systems.
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