Model-Based Analysis of Carbon Corrosion in Start-up/Shutdown, Fuel Starvation, and Voltage Reversal of a Polymer Electrolyte Fuel Cell

Support carbon corrosion has been identified as a major degradation source in a polymer electrolyte fuel cell. Start-up/Shutdown (SUSD) [1], fuel starvation [1], and voltage reversal [2] are widely-known conditions that can trigger non-negligible carbon corrosion in the anode or cathode. SUSD carbon corrosion is associated with current reversal while there is no external load. As a comparison, fuel starvation due to nitrogen blanketing and/or water droplets in an operating cell also can result in similar current reversal. The region with current reversal, i.e., a proton flux from the cathode to the anode, features extremely severe hydrogen depletion in the anode and occurrence of carbon corrosion in the opposite cathode. Differently, the voltage reversal occurs in one or a few cells (not all) in a stack. Those cells show negative cell voltages under extended reversal, but the overall current is flowing as usual thanks to the other normal cells in the stack. The voltage reversal leads to carbon corrosion in the anode, as compared to carbon corrosion in the cathode for current reversal. The local potential for carbon corrosion could be much more severe in an extended voltage reversal than that in SUSD. This paper/presentation will elucidate the fundamental differences of these three carbon corrosion scenarios with model simulation and analysis. The models [3, 4] will also be used to perform comprehensive parametric studies, aiming to understand the impacts from key design and operating parameters including pseudo-capacitance, selective oxygen evolution reaction (OER) catalysis, reactant gas flow rate, temperature, membrane hydration state, and current load drawn from the stack. It is anticipated to shed light on the otherwise confusing carbon corrosion scenarios in a polymer electrolyte fuel cell and the fundamental ideas for alleviation strategies. For example, in the fuel starvation induced carbon corrosion, the simulation indicates that the decreasing cell voltage due to diluted hydrogen concentration appears to limit the local potential in the cathode and associated carbon corrosion. In the SUSD carbon corrosion, pseudo-capacitance from Pt oxidation may raise another concern in parallel to carbon corrosion. In general, a reduced temperature or enhanced OER activity is helpful in reducing carbon corrosion. References: [1] W. Gu, P. T. Yu, R. N. Carter, R. Makharia, and H. A. Gasteiger, “Modeling and Diagnostics of Polymer Electrolyte Fuel Cells— Local H2Starvation and Start–Stop Induced Carbon-Support Corrosion”, Modern Aspects of Electrochemistry 49, Springer Science + Business Media, LLC, New York (2010). [2] S. Knights, D. Wilkinson, S. Campbell, J. Taylor, J. Gascoyne, and T. Ralph, “Solid Polymer Fuel Cell with Improved Voltage Reversal Tolerance”, U.S. Patent, 6,936,370 B1 (2005). [3] J. Chen, J. Siegel, T. Matsuura, and A. Stefanopoulou, “Carbon Corrosion in PEM Fuel Cell Dead-Ended Anode Operations”, Journal of the Electrochemical Society, 158, B1164-B1174 (2011). [4] J. Chen, J. Hu, and J. Waldecker, “A Comprehensive Model for Carbon Corrosion during Fuel Cell Start-Up”, Journal of the Electrochemical Society, 162, F878-F889 (2015). Figure 1. The schematic of carbon corrosion mechanisms from current reversal during start-up (upper subfigure) and voltage reversal (lower subfigure) in a polymer electrolyte fuel cell. Figure 1

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