Understanding the voltage reversal behavior of automotive fuel cells

Hydrogen starvation at the anode of a polymer electrolyte fuel cell (PEFC) causes cell voltage reversal followed by water electrolysis and carbon corrosion due to an increasing anode voltage. In addition to the conventional system control technologies to protect the cell from carbon corrosion, water electrolysis catalyst (e.g., IrO2) can be employed to protect the anode by promoting proton and electron production at anode by oxygen evolution reaction (OER) over carbon oxidation reaction. Here, we investigate the voltage reversal behavior of membrane-electrode assemblies (MEAs) with reversal-tolerant-anodes (RTAs) with OER catalyst to understand the degradation mechanism using electrochemical diagnostics and X-ray computed tomography. We found that the sustainable reversal time of the RTA MEAs scales with the IrO2 loading. However, all MEAs irrespective of the presence of IrO2 eventually fail. They exhibit a self-similar behavior of undergoing water electrolysis followed by the carbon corrosion under the reversal conditions. The cell performance decay is dominated by Ohmic resistance increase from anode structural collapse. From the post-mortem imaging, we do not detect any significant change in the distribution and morphology of IrO2 particles in the RTAs, suggesting that the RTA failure results from catalytic deactivation of the OER catalyst during cell reversal.