Grain-Boundary-Rich Mo-Doped RuO₂ for Highly Efficient and Stable Proton-Exchange-Membrane Water Electrolysis

RuO₂-based oxygen evolution reaction electrocatalysts have gained considerable attention as promising alternatives to replace expensive iridium-based materials in proton-exchange-membrane water electrolysis (PEMWE). Nevertheless, the structural destruction of RuO₂ and the dissolution of Ru atoms under high current densities hinder its instability. In this work, we introduced Mo into the RuO₂ lattice, which not only disrupted the long-range periodic structure but also the "site blocking" effect of Mo enabling the formation of ultrafine nanocrystals (4.3 nm) of RuO₂ with abundant grain boundaries (GB-Mo-RuO₂) at a higher temperature (500 °C). The developed GB-Mo-RuO₂ exhibited lower overpotentials of 185 and 280 mV and excellent stability of 450 and 150 h at 10 and 100 mA cm^-2, respectively. The introduction of Mo and GBs reduced the energy barrier in the rate-determining step and the solubility of Ru, thereby boosting both the activity and the stability of the catalyst. The PEMWE with GB-Mo-RuO₂ as the anode exhibited cell voltages of 1.65 and 1.85 V at 1 and 2 A cm^-2, respectively, and an extremely low decay rate (56.4 μV h^-1) at 1 A cm^-2 during 160 h.