3d-4d orbital hybridization over ruthenium-doped cryptomelane-type manganese dioxide for highly efficient oxygen evolution reaction

Developing efficient and durable oxygen evolution reaction (OER) electrocatalysts with reduced noble-metal content is essential for advancing sustainable water electrolysis technologies. Herein, a ruthenium-doped cryptomelane-type manganese dioxide (Ru-MnO 2 ) electrocatalyst is synthesized via a facile one-step hydrothermal method. Incorporating Ru 4+ into the MnO 2 lattice induces significant lattice distortion and creates abundant oxygen vacancies, accompanied by an increased Mn 3+ /(Mn 3+ +Mn 4+ ) ratio. The resulting Ru-MnO 2 catalyst delivers outstanding OER performance with a low overpotential of 179 mV at 10 mA cm −2 in 1.0 M KOH, surpassing pristine MnO 2 (408 mV) and even outperforming commercial RuO 2 (375 mV). Notably, Ru-MnO 2 also exhibits good activity under acidic conditions (193 mV at 10 mA cm −2 in 0.5 M H 2 SO 4 ), but stability needs to be further verified. Systematic mechanistic studies, including pH-dependence measurements and probe molecule experiments (TMA + , H 2 O 2 , KSCN, methanol), are consistent with an AEM-dominated pathway, where the reaction proceeds through surface-adsorbed intermediates derived from electrolyte OH − without the participation of lattice oxygen. Density functional theory (DFT) calculations reveal that Ru doping upshifts the density of states near the Fermi level, enhances electrical conductivity, and lowers the Gibbs free energy barrier for the rate-determining step. The strong 3d-4d orbital hybridization between Mn and Ru optimizes the adsorption energetics of OER intermediates (*OH, *O, *OOH), effectively breaking the linear scaling relationship and accelerating reaction kinetics. This work provides a promising strategy for designing high-performance, low-ruthenium OER electrocatalysts through electronic structure engineering.