Revealing Structure-Performance Relations in Core-Shell Catalyst Based PEM Water Electrolyzer Anodes with Low Iridium Loading

Reducing iridium loading in proton exchange membrane water electrolyzer anodes is essential to meet cost targets for large-scale green hydrogen production. Here, we report a photodeposition-based synthesis of TiO2@IrO2 core-shell catalysts with iridium contents as low as 10 wt%. The influence of annealing temperature, iridium content, and iridium loading on structural and electrochemical properties is systematically investigated. An annealing temperature of 450 °C provides the best compromise between activity, conductivity, and stability. Remarkably, even at 10 wt% Ir (≈ 4.5 vol% IrO2), the core-shell architecture maintains high electronic conductivity and mass activity. The low iridium content results in ~18 µm thick catalyst layers at a loading of 0.35 mgIr cm‑2, corresponding to a high thickness factor of 52.0 ± 0.8 µm (mgIr cm‑2)‑1. Two-dimensional, two‑phase performance modeling reveals that these thick catalyst layers improve electronic connectivity at low loadings, leading to higher catalyst utilization than a commercial reference. As a result, the core-shell catalyst outperforms the reference in single-cell measurements, achieving 1.77 V at 2 A cm‑2 at a low loading of 0.31 mgIr cm‑2. During 200 h durability testing, reversible degradation is observed, while irreversible losses remain on par with the reference and the core–shell structure is preserved.