To establish a recovery method for noble metals from membrane electrode assemblies (MEAs) of spent polymer electrolyte fuel cells (PEFCs) without the use of strong acids, electrochemical dissolution tests for Pt and Ru from MEAs were conducted. By using square potential waves, 93.2% of the Pt and 98.4% of the Ru dissolved from a MEA in 1 mol L −1 HCl at room temperature when oxidation and reduction potentials were at 1.5 and 0.1 V vs. SHE and the holding times for both were 15 s per cycle. The dissolution of Pt and Ru became remarkable when the oxidation potential was 1.4 V vs. SHE and gradually decreased at more positive potentials. These results indicate that competitive reactions exist in the dissolution process. In addition, the effects of H + and Cl − concentrations on the dissolution ratios were investigated. The dissolution ratios of Pt and Ru were small in solutions with low Cl ). Thus, we veri ed that the electrochemical dissolution method was adaptable to the recovery of noble metals from MEAs and that strong acids were not needed.

The mechanism of electrochemical reactions of rhenium species at stainless steel 316 electrodes and the effect of the pH in 0.5 M (NH 4 ) 2 SO 4 solutions containing 5 mM HReO 4 (pH 1, 3, and 10) were investigated by electrochemical measurements and surface analyzes of the rhenium-deposited electrodes. From the results of cyclic voltammetry, we found that ReO 4 − anion was electrochemically active and the electrodeposition of rhenium species was accelerated after hydrogen evolution occurred, whereas ReO 4− anion was inactive before hydrogen evolution occurred. This indicates that adsorbed hydrogen atom on the electrodes is needed to reduce ReO 4 − anion. The deposits obtained by potentiostatic electrolysis at a potential lower than that of the hydrogen evolution reaction were analyzed by XPS and SEM. In the pH 1 solution, the deposit was metallic Re, whereas in the pH 3 and 10 solutions, the deposit was a mixture of metallic Re, ReO 2 , and ReO 3 . From the results of anode stripping voltammetry, it was found that the metallic Re was oxidized to ReO 4 − via ReO 3 or ReO 2 .

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