Boosting Water Oxidation through In Situ Electroconversion of Manganese Gallide: An Intermetallic Precursor Approach

For the first time, the manganese gallide (MnGa₄ ) served as an intermetallic precursor, which upon in situ electroconversion in alkaline media produced high-performance and long-term-stable MnO_x -based electrocatalysts for water oxidation. Unexpectedly, its electrocorrosion (with the concomitant loss of Ga) leads simultaneously to three crystalline types of MnO_x minerals with distinct structures and induced defects: birnessite δ-MnO₂ , feitknechtite β-MnOOH, and hausmannite α-Mn₃ O₄ . The abundance and intrinsic stabilization of Mn^III /Mn^IV active sites in the three MnO_x phases explains the superior efficiency and durability of the system for electrocatalytic water oxidation. After electrophoretic deposition of the MnGa₄ precursor on conductive nickel foam (NF), a low overpotential of 291 mV, comparable to that of precious-metal-based catalysts, could be achieved at a current density of 10 mA cm^-2 with a durability of more than five days.