Influence of Defects on Activity-Stability of Cu1.5Mn1.5O4 for Acid-Mediated Oxygen Evolution Reaction

The spinel oxide, Cu1.5Mn1.5O4 (CMO) is a promising precious group metal-free electrocatalyst (EC) known for acid-mediated oxygen evolution reaction (OER). By employing density functional theory (DFT) based Bader analysis for active sites identification, the effective electronic charges of constituent ions in the ordered-disordered crystal structures were calculated. Accordingly, for DFT result validation, structurally disordered Cu1.5Mn1.5O4 ECs were experimentally synthesized by heat treatment to 200 °C (CMO-200). The disorder-order transitions of CMO related change in surface atomic arrangement and alteration in the Mn3+/Mn4+ and Cu2+/Cu1+ states are modulated via corresponding heat treatment (200 °C-800 °C) of CMO, revealing significant influence on OER electrocatalytic activity and durability. The measured higher electrocatalytic activity of disordered CMO-200 contrasted with ordered CMO is attributed to higher Mn3+/Mn4+ and Cu2+/Cu1+ states, signifying the beneficial role of Mn3+ and Cu2+ for facilitating OER. The ordered CMO structures containing lower Mn3+/Mn4+ and Cu2+/Cu1+ ratios albeit reveal higher electrochemical stability than the disordered CMO. The present study, thus, provides fundamental insights into the influence of ordered-disordered structures and rearrangement of the oxidation state of active species and their combined synergistic effects on the electrochemical performance for engineering high-performance ECs for acidic OER.