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

For the first time, the manganese gallide (MnGa(4)) 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‐MnO(2), feitknechtite β‐MnOOH, and hausmannite α‐Mn(3)O(4). 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 MnGa(4) 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.