The catalysts of choice in polymer electrolyte fuel cells (PEFCs) remain Pt-based nanoparticles on high-surface-area carbon support. One critical challenge facing commercialization of this fuel cell is the gradual decline in performance during operation, mainly caused by the loss of electrochemical surface area (ECA) of the Pt or Pt alloy nanoparticles at the cathode. In this respect, the understanding of the dominant mechanisms of the loss of ECA and loss of oxygen reduction activity, such as the electrochemical dissolution of Pt or the transition metal alloy component, is of vital importance. Several mechanisms for dissolution of platinum have been proposed including direct Pt dissolution and electrochemical oxidation of the Pt surface atoms followed by chemical dissolution of the resulting Pt surface oxide.

This presentation will outline the dissolution of PtCo under various operating conditions. Studies are performed to quantify the amount of dissolved Co and Pt during potentiodynamic conditions in an electrochemical flow cell system connected to an inductively-coupled plasma-mass spectrometer (ICP-MS) capable of detecting trace concentrations (<ppb) of dissolved elements in solution. The electrochemical data combined with the ICP-MS data are used to evaluate the influence of various factors such as potential, potentiodynamic profile parameters (e.g., scan rate, upper and lower potential limits), particle size, and support type on the dissolution processes in acidic electrolytes at room temperature.

Preliminary measurements showed that Pt dissolution occurs during both the positive-going and negative-going potential sweeps. When the potential was cycled from 0 to 1.0 V_RHE, two distinct dissolution peaks were detected by the ICP-MS online analysis. The ratio of the amount of Pt dissolved during the two sweeps was found to be dependent on the sweep rate, potential hold times, and potential profile. Fundamental models will be developed to explain the mechanisms of degradation process under various potential conditions.

This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability Consortium (FC-PAD). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.