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 Spectroscop

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• 作者：Qingying Jia ; David E. Ramaker ; Joseph M. Ziegelbauer ; Naggapan Ramaswamy ; Aditi Halder ; Sanjeev Mukerjee
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：March 7, 2013
• 年：2013
• 卷：117
• 期：9
• 页码：4585-4596
• 全文大小：531K
• 年卷期：v.117,no.9(March 7, 2013)
• ISSN：1932-7455

文摘

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鈥?.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鈥?.3 V vs RHE), concentrations of Cu²⁺ as low as 10 渭M were found to coat the active Pt surfaces, thereby drastically inhibiting the hydrogen oxidation reaction. Over the Cu underpotential deposition region (0.35鈥?.70 V vs RHE), Cu²⁺ concentrations 鈮?.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鈥揅u scattering paths below 0.84 V, Cu was not observed at higher potentials. The 螖渭 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 螖渭 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.