On the interface electron transport problem of highly active IrOx catalysts

Abstract

Electron transport resistance at the interface between the catalyst layer (CL) and the porous transport layer (PTL) in the PEMWE anode has long been poorly understood despite its significant impact on performance. In this study, we demonstrate that highly active IrO_x nanocatalysts encounter electron transport problems at the interface with the native oxide (TiO_x) on the Ti PTL, leading to poor single-cell performance. This issue is attributed to the pinch-off effect caused by the ionomer, which withdraws electrons from TiO_x at the interface, creating a severe electron depletion layer. The problem is further exacerbated at the TiO_x interface of ultrafine IrO_x nanocatalysts, as small-sized catalyst particles form dense CL structures, amplifying the influence of the expanded ionomer/TiO_x interface on the entire region. By manipulating the particle size of the IrO_x catalyst, we demonstrate this effect at the single-cell level and further validate it through COMSOL Multiphysics simulations. Our findings reveal that IrO_x catalysts larger than 20 nm are necessary to mitigate the significant interference caused by the ionomer at the TiO_x interface. This work provides critical insights into optimizing catalyst particle dimensions to overcome the pinch-off effect and enhance performance.