Stabilizing Hypervalent Ru Sites in RuO2 Catalysts by Synergistic Bimetal Codoping for Long-Lasting Ampere-Level PEM Water Electrolysis

Abstract

Exploring feasible Ir-free anode catalysts is pivotal for large-scale implementing proton exchange membrane water electrolysis (PEMWE) to produce green-H₂. Here we demonstrate that synergistic Mo and Rh codoped RuO₂ (Mo,Rh-RuO₂) catalysts can strengthen hypervalent Ru sites to break the activity-stability tradeoff in sluggish oxygen evolution reaction (OER), realizing long-lasting ampere-level PEMWE. Cross-linked ultrafine Mo,Rh-RuO₂ nanocatalysts are synthesized via a simple molten salt method. The sample exhibits significant low overpotentials for OER, e.g. 208 mV at 100 mA cm^-2, with excellent stability. In an PEM electrolyzer, it requires only 1.58 and 1.87 V cell voltages to respectively reach 1.0 and 3.0 A cm^-2 current densities and exhibits a minimal decay of only 0.03 mV h^-1 at 1.0 A cm^-2 for over 2000 h durability test. Such superior OER and electrolyzer performances outperform most the cutting-edge electrocatalysts. Mechanism studies indicate that the Mo,Rh-RuO₂ catalyst possesses significantly increased OER-active hypervalent Ru and strengthened Ru−O bonds. A great portion of reaction paths are converted from habitual lattice oxygen evolution mechanism to adsorbate evolution mechanism, greatly suppressing the consumption of lattice oxygen. Moreover, the Mo,Rh-RuO₂ catalysts possess crucial self-healing ability of oxygen vacancies and stabilized surface hypervalent Ru sites for drastically boosting long-term stability.