Analysis of Voltage Losses in PEM Water Electrolyzers with Low Platinum Group Metal Loadings

In this study, the influence of catalyst loading on the performance of a proton exchange membrane (PEM) water electrolyzer is investigated (Nafion 212 membrane; IrO 2 /TiO 2 (anode) and Pt/C (cathode)). Due to the fast kinetics of the hydrogen evolution reaction (HER) on platinum (Pt), the Pt loading on the cathode can be reduced from 0.30 mg Pt cm −2 to 0.025 mg Pt cm −2 without any negative effect on performance. On the anode, the iridium (Ir) loading was varied between 0.20–5.41 mg Ir cm −2 and an optimum in performance at operational current densities (≥1 A cm −2 ) was found for 1–2 mg Ir cm −2 . At higher Ir loadings, the performance decreases at high current densities due to insufficient water transport through the catalyst layer whereas at Ir loadings <0.5 mg Ir cm −2 the catalyst layer becomes inhomogeneous, which leads to a lower electrochemically active area and catalyst utilization, resulting in a significant decrease of performance. To investigate the potential for a large-scale application of PEM water electrolysis, the Ir-specific power density (g Ir kW −1 ) for membrane electrode assemblies (MEAs) with different catalyst loadings is analyzed as a function of voltage efficiency, and the consequences regarding catalyst material requirements are discussed.