Irreducible IrO2 Anode Co-Catalysts for PEM Fuel Cell Voltage Reversal Mitigation and Their Stability Under Start-Up/Shut-Down Conditions

IrO₂ has been widely used as the anode co-catalyst for mitigating cell voltage reversal damages in proton exchange membrane fuel cells (PEMFCs). However, under the PEMFC anode operation conditions, conventionally prepared IrO₂ catalysts are reduced by H₂, forming metallic Ir on their surface, which is prone to dissolution during start-up/shut-down (SUSD) cycles. The dissolved Irⁿ⁺ ions can permeate through the membrane to the cathode electrode, poisoning the oxygen reduction reaction (ORR) activity of the Pt/C cathode catalyst. In this study, we introduce an unprecedented approach to synthesize IrO₂ catalysts (irr-IrO₂) which are not reduced in the PEMFC anode environment at 80 °C over extended time. Their preparation is based on an industrially scalable procedure, consisting of a high-temperature (650 °C–1000 °C) heat treatment step, a subsequent ball milling step, and a final post-annealing step, thereby attaining catalysts with specific surface areas of ∼25 m² g⁻¹. The high reduction resistance of the irr-IrO₂ catalysts, attributed to their highly ordered crystalline structure compared to that of typically synthesized IrO₂ catalysts, is reflected by the observation that SUSD cycling of MEAs with the irr-IrO₂ as anode co-catalysts does not result in iridium dissolution and the associated iridium poisoning of the Pt/C cathode catalyst.