Cathode Platinum Degradation in Membrane Electrode Assembly Studied Using a Solid-State Electrochemical Cell

The electrochemical dissolution of the Pt cathode catalyst, which determines the lifetime of polymer electrolyte fuel cells (PEFCs), has been studied. A newly developed solid-state electrochemical cell, which consisted of a Nafion membrane sandwiched by Pt/C-based catalyst layers, was employed for the electrochemical measurement. When humidified O2 and H2 gases were supplied to working and counter electrodes, respectively, the Pt electrochemical surface area (ESA) decreased during the potential cycle for 20 h. The highest rate of ESA decrease was recorded for an alternating potential cycle between (i) a positive-potential region of 0.2−0.65 V vs Ag/Ag2SO4 and (ii) a negative-potential region of −0.73 to −0.4 V vs Ag/Ag2SO4. From an SEM−EDS observation of the cross section of a membrane sample after the potential cycle, Pt particles are found in the Nafion membrane, indicating that the decrease in ESA caused by Pt dissolution brings about the Pt deposition in the membrane. Under the assumption that O2 redu...

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