B‐Doped Manganese Dioxide Achieves Synchronous Multi‐Scale Structural Regulation for Enhanced Oxygen Evolution Reaction Electrocatalytic Performance

Manganese dioxide (MnO ₂ ), as a promising electrocatalyst for the oxygen evolution reaction (OER), is limited in practical application by its poor electrical conductivity and insufficient exposure of active sites. In this study, a boron (B) doping strategy is proposed, in which ammonium pentaborate tetrahydrate (NH ₄ B ₅ O ₈ ·4H ₂ O) is introduced during a hydrothermal process to synthesize α‐MnO ₂ with a nanoneedle‐like structure rich in oxygen vacancies (O _V ) and Mn ³⁺ content. Systematic characterization combined with density functional theory calculations reveals that B doping not only induces a crystal‐phase transition from β‐MnO ₂ to α‐MnO ₂ possessing a large‐tunnel structure, accompanied by the formation of a high‐surface‐area nanoneedle morphology, but also promotes the generation of O _V and significantly increases the Mn ³⁺ content. Electrochemical tests show that the optimized B‐doped MnO ₂ requires an overpotential of only 411 mV to achieve a current density of 10 mA cm ⁻² in 1 M KOH electrolyte. Its OER performance surpasses that of most reported powder‐based MnO ₂ catalysts and demonstrates good stability.