Crystal Phase‐Dependent Performance of RuO x /MnO 2 Nanorods for Alkaline Oxygen Evolution Reaction

Abstract MnO 2 is a widely studied non‐noble metal electrocatalyst for the oxygen evolution reaction (OER) and has demonstrated phase‐dependent performance. Among the various MnO 2 polymorphs, γ‐MnO 2 has abundant defects and vacancies due to its disordered crystal structure of both β‐MnO 2 and R‐MnO 2 intergrowth, thus being a potential high‐performance OER catalyst. However, γ‐MnO 2 has been studied much less than other crystal phases of MnO 2 , and γ‐MnO 2 ‐based heterostructures are rarely reported. In this study, it is discovered that γ‐phase plays a unique role in RuO x /MnO 2 heterostructured nanorods. Among the pristine α‐, β‐, and γ‐MnO 2 polymorphs, α‐phase shows the best OER activity; however, after loading RuO x nanoclusters, RuO x /γ‐MnO 2 shows the largest enhancement and hence the best OER activity with an overpotential of 255 mV at 10 mA cm −2 and excellent stability (> 300 h), which is much superior to the commercial RuO 2 catalyst. Furthermore, when tested in an anion exchange membrane water electrolyzer (AEMWE), it maintains excellent durability at 200 mA cm −2 over 380 h. Mechanistic study shows that RuO x /γ‐MnO 2 exhibits the strongest electron transfer between Ru and Mn, which significantly weakens the Mn‐O bond strength and reduces the interaction between intermediates and the MnO 2 surface, ultimately resulting in the lowest energy barrier for the reaction.