Ionomer Effect Investigation and Gradient Ionomer Design of Anode Catalyst Layers for PEM Water Electrolysis

The ionomer content significantly affects the microstructures and electrochemical performance of catalyst layers (CLs) in proton exchange membrane water electrolysis (PEMWE). Here, this work explores the effects of ionomer content on CL structure, electrochemical performance, and durability. These findings demonstrate that the ionomer content optimization involves the trade-off between ohmic impedance and combined activation/mass transport impedances. Specifically, excess ionomers induce catalyst agglomeration and, thus, decrease the electrochemical reaction kinetics and effective electrochemical reaction area, thereby increasing the activation and mass transport impedances. However, fewer ionomers significantly lead to poor proton conduction and durability. To overcome these limitations, we propose a dual CL design featuring a gradient of ionomer content from the membrane side to the porous transport layer side. This gradient CL design achieves a superior performance of 1.81 V at 3.0 A cm–2 under an iridium loading of 1.0 mg cm–2, which exhibits a voltage reduction of 35 mV compared to the single-layer CL. Moreover, the gradient CL increases the voltammetric charge by over 10% compared to the single-layer CL. This advancement in electrochemical performance is accompanied by better CL durability.