Activating in-plane dead zones of anode catalyst layers in proton exchange membrane water electrolyzers

The utilization of iridium-based anode catalysts in proton exchange membrane water electrolyzers is largely limited by the presence of electrochemically inactive "dead zones" within the catalyst layer. Here, by combining in-situ visualization of gas bubble evolution with quantitative conductivity measurements and electrochemical analysis, we establish that the limited in-plane electronic conductivity, dictated by the ionomer disrupting the conductive network of IrO₂ nanocatalysts, is the dominant factor. A sequential spray-coating strategy is further developed, which decouples the deposition of a pristine conductive catalyst layer from the ionomer and thereby preserves continuous electron transport pathways. This approach effectively activates the in-plane dead zones, resulting in membrane electrode assemblies that exhibit over 30% higher activity (4.2 A cm^-2@2.0 V@80 °C; membrane: Nafion 115) than those prepared by the conventional one-step method based on IrO₂/ionomer mixed inks. Crucially, this approach achieves both low iridium loading (0.25 mg cm^-2) with standard catalysts and demonstrates extended stability over 8300 hours under practical current densities.