Achieving Pt-coating-free anodes using double-layered catalyst layer structure for polymer electrolyte membrane water electrolysis

Abstract

Achieving high-performance and cost-effective proton exchange membrane water electrolysis (PEMWE) necessitates a reduction in the use of precious group metals (PGMs) while maintaining electrolysis efficiency. However, commercial high-activity IrO_x catalysts often fail to deliver optimal performance at low loadings because of electron transport problems caused by the natural oxide (TiO_x) on the Ti porous transport layer (PTL) surface. This is because the high work functions of IrO_x catalysts create Schottky barriers in the low-work-function TiO_x, thereby deteriorating the electrical conductivity at the interface. The Pt coating is commonly employed as a protective layer; however, hundreds of nanometers of coating significantly increase the cost of the electrolyzer. To address this challenge, we propose a double-layered catalyst layer (DL-CL) structure that enables the fabrication of Pt-coating-free anodes, with crystalline, low-work-function rutile IrO₂ (R-IrO₂) positioned at the PTL interface and highly active IrO_x (HA-IrO_x) positioned on the membrane side. The key advantage of the R-IrO₂ layer over the Pt coating is its porous structure, which effectively prevents contact between HA-IrO_x and TiO_x with much lower loading (0.05–0.2 mg cm⁻²). The DL-CL minimizes the influence of TiO_x on both performance and durability while enabling all PGMs to actively participate in the oxygen evolution reaction.