Crystal Splintering of β‑MnO₂ Induced by Interstitial Ru Doping Toward Reversible Oxygen Conversion

Among the various polymorphs of manganese oxides, β-MnO₂ has been long regarded as an inert electrocatalyst for oxygen conversion due to its high thermodynamic stability and consummate lattice structure. Herein, for the first time, we report the phenomenon of crystal splintering induced by interstitial atomic doping for drastically enhancing the activities of both oxygen evolution (OER) and oxygen reduction (ORR) reactions for β-MnO₂. Ru-doped β-MnO₂ exhibits an ultralow OER and ORR voltage gap of only 0.63 V, which is the best ever observed for β-MnO₂ and surpasses many state-of-the-art bifunctional oxygen catalysts reported to date. Through advanced microscopic and spectroscopic characterizations, in conjunction with theoretical understandings, the drastically improved OER activity is attributed to the highly under-coordinated Ru–O sites exposed on the surface upon crystal splintering, while the enhanced ORR property originates from the strained M–O configuration with enriched Mn³⁺ content and oxygen vacancies.