| 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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