Understanding Electrochemical Degradation of Polymer Electrolyte Fuel Cell Catalysts Using Time-Resolved Measurements

Abstract

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 and, if an alloy, loss of the base metal alloying component (e.g., Co, Ni, or Fe). 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 base metal, 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. Our previous measurements on PtCo catalyst showed that degradation of PtCo/C catalysts due to Pt dissolution is greatly accelerated by the reduction of PtOx species formed at potentials >0.9 V and that accelerated Co loss is also associated with reduction of the oxides formed at >0.9 V. 1 This presentation will outline effects of type of Pt alloy catalyst (e.g., solid solution, ordered intermetallic, shape-controlled) on Pt and alloying element dissolution rates as a function of number of accelerated stress test cycles. Studies are performed to quantify the amount of dissolved base metal 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), atomic structure, and base metal content on the dissolution processes of alloy catalysts in acidic electrolytes at room temperature. Fundamental models will be developed to explain the mechanisms of degradation process for the various catalyst types under various potential conditions. References K. Ahluwalia, D. D. Papadias, N. Kariuki, J. K. Peng, X. P. Wang, Y. Tsai, D. Graczyk, and D. J. Myers, J Electrochem Soc, 165, F3024 (2018) 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.