Catalyst Layer Composition Effects in Proton Exchange Membrane Water Electrolysis

Abstract The increasing demand for hydrogen necessitates reducing the capital cost of proton exchange membrane water electrolyzers (PEMWEs). A key approach is to reduce iridium loading while maintaining the high performance and durable operation. This requires optimization of the catalyst layer composition and minimization of interfacial contact resistance with the porous transport layer (PTL). This study investigates the effects of varying anode and cathode catalyst layer compositions on short-term and long-term performance of PEMWEs. The impact of reducing the IrOx loading from 1.0 to 0.5 mg∙cm–2, decreasing the anode ionomer content to 50%, and reducing the cathode ionomer content to 50% was evaluated. Performance was assessed through comparison of the Tafel slope, Tafel constant, charge transfer resistance, and ohmic resistance. The results indicate that performance losses were significantly reduced using a PTL with a high contact area when IrOx loading was reduced by 50%. However, reducing anode loading or ionomer content decreased catalyst layer thickness and ohmic resistance but slightly increased the Tafel constant. During long-term operation, no significant difference between the cell voltages was observed, attributed to higher irreversible losses that occurred with 0.5 mg∙cm–2 loading. In contrast, 50% reduction in cathode ionomer content led to significant improvement in performance, evidenced by reduced kinetic and ohmic losses in both short- and long-term operations.