Is high specific surface area essential for anode catalyst supports in proton exchange membrane water electrolysis?

Abstract

Dispersing iridium onto high-specific-surface-area supports is a widely adopted strategy to maximize iridium utilization in anode catalysts of proton exchange membrane water electrolysis (PEMWE). However, here we demonstrate that the overall cell performance, including initial efficiency and long-term stability, does not benefit from the typical high specific surface area of catalyst supports. The conventional understanding that high iridium utilization on high-specific-surface-area supports increases activity holds only in aqueous electrolytes, while under the typical working conditions of PEMWE, the mass transport within the anode catalyst layers plays a more significant role in the overall performance. Particularly, the iridium oxide on the supports with 10-fold lower specific surface area exhibited an almost 3-fold lower decay rate without sacrificing original performance, owing to the enhanced mass transport enabled by the porous electrode structure. By further decreasing the Ir loading of catalysts, the advantages of low-surface-area supports became more pronounced, as the resulting anode achieved both enhanced performance and durability-demonstrating a 98 mV lower cell voltage and maintaining an exceptionally low degradation rate of only 8.8 μV h^-1 over 1900 hours at 2.0 A cm^-2, corresponding to a nearly 10-fold improvement. These findings can help guide the rational design of catalysts for practical, low-cost PEMWE.