How the Porous Transport Layer Dictates Membrane Electrode Assembly Performance of IrO 2 Catalysts

ABSTRACT Reducing the use of precious metals is essential for the commercialization of proton exchange membrane water electrolysis (PEMWE). The Schottky contact formed between the catalyst layer and Ti porous transport layer (PTL) at the anode significantly degrades cell performance and necessitates high Ir loading or Pt coating. IrO 2 catalysts with various crystallite sizes (1.7‒11.0 nm) were synthesized, and their membrane electrode assembly (MEA) performance was evaluated at a low Ir loading of 0.3 mg Ir cm −2 using Pt‐coated Ti PTL and bare Ti PTL. The MEA performance exhibited opposite trends depending on the type of PTL, primarily due to variation in the work function, which is determined by the surface oxygen configuration of the IrO 2 catalyst. Smaller crystallites exhibited a larger work function, resulting in a greater performance discrepancy between the two PTL types. To overcome the suboptimal performance of IrO 2 , we utilized the crystalline 7.1 nm‐sized IrO 2 as an electron pathway and deposited highly active amorphous IrO x on its surface. This mixed‐phase Ir oxide exhibited good cell performance and durability even with a bare Ti PTL. This study highlights that the Schottky contact problem of IrO 2 catalysts can be overcome through surface engineering, enabling low Ir use for PEMWE.