Tailoring MMn2O4 Spinels Anchored on Nitrogen doped Reduced Graphene Oxide for High Performance Bifunctional Water Splitting

Abstract

Developing highly efficient, durable, and low-cost oxygen evolution reaction (OER) electrode remains a key barrier that needs to be overcome for producing green H2 through alkaline water electrolysis (AWE). A series of transition metal cation-substituted manganese oxides (M-Mn2O4, where M = Co, Cu, Fe, and Zn) over nitrogen-doped rGO (N-rGO) nanosheet (M-Mn2O4@N-rGO) heterostructures using a facile solvothermal strategy were developed. Among the tested compositions, the FeMn2O4@N-rGO heterostructures exhibited superior OER catalytic activity, with an overpotential (η) of ~330 mV at 10 mA cm-2 along with stability over 96 h in 1 M KOH. In addition to OER activity, the FeMn2O4@N-rGO heterostructure exhibited better hydrogen evolution reaction (HER) performance, achieving an overpotential of 153 mV at a current density 10 mA cm-2. The coexistence of Fe3+/Fe2+ and Mn3+/Mn4+ redox couples provide multiple electron transfer pathways during water splitting. When assembled as a bifunctional electrode for overall water splitting (FeMn2O4@N-rGO as both anode and cathode), the system delivers a cell voltage of 1.57 V at 10 mA cm-2, with operational stability over 10 h. The robust spinel framework, strong metal–support interactions confirm that FeMn2O4@N-rGO is a viable electrocatalyst for AWE systems