Electrochemical Formation of a MnO₂ Nanoshield on Ru-Doped Mn₃O₄ for Ultrastable Acidic Oxygen Evolution Catalysis

Proton exchange membrane (PEM) water electrolysis is a promising strategy for large-scale hydrogen production; however, its industrial feasibility is hampered by the lack of highly active and durable oxygen evolution reaction (OER) catalysts in acidic environments. Ru-based catalysts offer high intrinsic activity but are susceptible to dissolution and structural degradation. To address this, this study proposes an electrically induced "nanoshield" strategy. A Ru single atom-doped Mn₃O₄ (Ru-Mn₃O₄) catalyst enables the in situ spontaneous reconstruction of the catalyst surface structure. Under an electric field, Mn₃O₄ crystals undergo interlayer slip and polarization rotation, inducing the growth of a porous MnO₂ nanoshield on the catalyst surface, that effectively inhibits the dissolution of Ru active sites without compromising reaction activity. The catalyst exhibits excellent OER performance, delivering 10 mA cm_geo^-2 at an overpotential of only 176 mV in 0.5 M H₂SO₄, and remains stable for over a year (8800 h) at a current density of 50 mA cm_geo^-2. The PEM electrolyzer based on Ru-Mn₃O₄ shows a decay rate of 0.15 mV h^-1 at 1000 mA cm_geo^-2 and only 0.06 mV h^-1 at 500 mA cm_geo^-2, outperforming commercial RuO₂. This study provides a new path for the construction of high-performance acidic OER catalysts and demonstrates the great potential of the nanoshield strategy in electrocatalytic structural protection.