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Fundamental Aspects of ad-Metal Dissolution and Contamination in Low and Medium Temperature Fuel Cell Electrocatalysis: A Cu Based Case Study Using In Situ Electrochemical X‑ray Absorption Spectroscopy
Ist Teil von
Journal of physical chemistry. C, 2013-03, Vol.117 (9), p.4585-4596
Ort / Verlag
Columbus, OH: American Chemical Society
Erscheinungsjahr
2013
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
Electrochemical methods (cyclic voltammetry and rotating ring disk electrode) and in situ X-ray absorption spectroscopy (XAS) were used in conjunction to study copper adsorption onto carbon-supported platinum nanoparticles over the operating potential range of proton exchange membrane fuel cell (PEMFC) cathodes and anodes (∼0.0–1.0 V vs the reference hydrogen electrode, RHE). Our purpose was to better understand the detrimental effects of Cu leaching from high-activity dealloyed PtCu x electrocatalysts. These studies were conducted in CuSO4-doped 0.1 N solutions of HClO4 and H2SO4 under both inert and oxygenated conditions. Over the anode potential range (∼0.0–0.3 V vs RHE), concentrations of Cu2+ as low as 10 μM were found to coat the active Pt surfaces, thereby drastically inhibiting the hydrogen oxidation reaction. Over the Cu underpotential deposition region (0.35–0.70 V vs RHE), Cu2+ concentrations ≥0.05 mM resulted in Cu deposition onto Pt. This was found to lower the oxygen reduction reaction activity of Pt by skewing the reaction mechanism toward the two-electron pathway (peroxide production) away from the desired four-electron pathway (water). Electrochemical methods were inconclusive as to the effects of Cu2+ at potentials greater than 0.84 V. While in situ Pt L3 edge extended X-ray absorption fine structure (EXAFS) revealed definitive Pt–Cu scattering paths below 0.84 V, Cu was not observed at higher potentials. The Δμ analysis of X-ray absorption near-edge structure (XANES) revealed that Cu(O) coadsorbs under high Cu2+ concentrations in HClO4, and that H2SO4 results in Cu(O) coadsorption at lower concentrations. Extending the Δμ analysis to lower potentials revealed the interplay of Cu2+, O(H), and H+ coadsorption with respect to potential, Cu2+ concentration, and sparging environment (inert or oxygenated). These studies verify that Cu leaching from PtCu x -alloy electrocatalysts can have detrimental effects on both the anode and cathode sides of a PEMFC, and similar experiments can be extended to probe the adsorption effects of other transition metals from PtM x alloys.