Construction of An Efficient Electrode with Ionomer Binding Sites for Stable Water Electrolysis

Performance discrepancy between laboratory-scale catalysts and practical electrodes in real devices are widely observed. However, the fundamental causes of this discrepancy remain poorly understood, hindering the translation of advanced academic technologies into industrial practice. Using representative IrO2/TiO2 anode catalysts in proton exchange membrane water electrolyzer (PEMWE) as examples, we demonstrate this gap originates from the catalyst-electrolyte interface and can be effectively addressed by the new concept of ionomer binding sites (IBSs) in this work. Although Norm-Catal. (IrO2 on rutile TiO2) exhibited fourfold higher mass activity than IBS-Catal. (IrO2 on anatase TiO2) in aqueous electrolytes, the PEMWE device employing IBS-Catal. achieved twofold higher mass activity and a 24-fold longer predicted lifetime. The key lies in the IBSs: stronger ionomer binding on exposed anatase TiO₂ facilitated efficient and robust mass transport while mitigating active site poisoning. Moreover, the IBSs also enabled a facile scale-up of electrode fabrication by slot-die coating, a typical industry process, from which a 5.5 kilowatt PEMWE stack surpassed the 2026 DOE target. This work highlights that catalyst design should pay more attention to IBSs, rather than focusing solely on active sites.