Ta-Based Catalyst Support for Proton Exchange Membrane Fuel Cell Applications
Bibliographic record
Abstract
Proton Exchange Membrane Fuel Cells (PEMFCs) are promising energy conversion devices. However, corrosion of the carbon catalyst support at the cathode is one of the main problems that is impeding commercialization of PEMFCs and, therefore, the development of a durable catalyst support material is a major technical objective. PEMFCs typically use carbon black as the support material for Pt nanoparticles. However, carbon is susceptible to electrochemical corrosion, especially under conditions of fuel starvation during startup/shutdown cycles. Therefore, alternative catalyst supports, with many based on metal oxides (e.g., Ta2O5, TiOx, WOx, SnO2, IrO2), carbides (e.g., WCx), metal nitrides (e.g., TixNy), etc., have been investigated to replace carbon. These metal oxides/carbides/nitrides/oxynitride have been reported to have good corrosion resistance under PEMFC operating conditions, but their conductivity needs to be improved, especially compared to carbon. Therefore, carbon is often added, forming composite materials. Furthermore, these alternative materials may offer strong metal/support interactions (SMSI), potentially enhancing catalyst activity and durability. Although Ta2O5/C composites have been investigated as a support material previously, no work has yet been reported on the use of TaOxNy/C for this purpose. TaOxNyis a material under study in our group, normally in the form of nanotubes. The authors examine the properties of TaOxNy nanoparticle (NP)/CIC (colloidal imprinted carbon) composites as supports for Pt nanoparticles, specifically for use in PEMFC cathodes, and the influence of the synthesis method of the TaOxNy NPs/ CIC/Pt NPs on the durability of the catalyst support. This presentation has a specific focus on the effect of the method of preparation of TaOxNy NPs/CIC/Pt NPs on catalyst durability. It has been reported earlier that, when metal oxides are synthesized in the presence of a carbon support, they deposit preferentially on the defects or oxygenated sites, similar to Pt NPs, thus blocking some of the COR initiation sites (oxygenated functional groups on the carbon) by utilizing them to anchor the NPs. Thus, we have used hydrothermal synthesis to first deposit a Ta oxide precursor on the CIC surface, where Ta alkoxide is hydrolysed to Ta oxide at high temperatures (250 oC) in an autoclave. In the second approach, pre-prepared Ta oxide NPs were physically mixed with the CIC powder, assuming that the preferential deposition of the Ta oxide NPs on the oxygenated sites of the CIC would not occur, hence predicting a lower durability of this composite material. After formation of Ta oxide NPs/CIC by these two methods, the samples were subjected to ammonolysis to obtain TaOxNyNPs/CIC, which were then functionalized with various wt % of Pt NPs by the incipient wet impregnation method. Scanning and Transmission electron microscopies were used to determine the structure, morphology, and composition of these composite support materials, while cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to determine electrochemical characteristics and durability as a catalyst support. The results have shown that the TaOxNy NPs were successfully hydrothermally synthesized on the surface of the CICs. For the 80 nm pore size CIC, the size of the TaOxNy NPs is 30-70 nm, presumed to be depositing both outside and inside the pores of the CIC nanostructure. The TaOxNy NPs also exhibit regular voids in their structure, assumed to arise from the higher density of TaOxNy (14 g·cm-3) relative to that of the Ta oxide precursor (8.2 g·cm-3). A systematic study of the electrochemical properties of both of the composites, as well as of the CIC component, was performed at each stage of the synthesis. It was found that the conductivity of the CIC improves somewhat after exposure to the ammonia environment, consistent with its significantly enhanced N content. Also, TaOxNy is electrochemically active negative of 0.6 V vs. RHE, giving a reversible redox feature proposed to be due to the Ta5+/4+ redox reaction. Accelerated durability tests carried out by potential stepping between 0.8 and 1.4 V in acidic solutions showed that the TaOxNy NPs/CIC materials are more corrosion resistant than the CIC alone. Overall, the use of hydrothermally synthesized TaOxNy NPs, combined with nitrided CIC, appears to be a promising route towards achieving enhanced corrosion resistance support materials for PEMFC cathode applications.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".