Influence of Defects on Activity-Stability of Cu <sub>1.5</sub> Mn <sub>1.5</sub> O <sub>4</sub> for Acid-Mediated Oxygen Evolution Reaction
Shrinath Dattatray Ghadge, Moni Kanchan Datta, Oleg I. Velikokhatnyi, Ramalinga Kuruba, Pavithra Murugavel Shanthi, Prashant N. Kumta
Abstract
The spinel oxide, Cu 1.5 Mn 1.5 O 4 (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 Cu 1.5 Mn 1.5 O 4 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 Mn 3+ /Mn 4+ and Cu 2+ /Cu 1+ 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 Mn 3+ /Mn 4+ and Cu 2+ /Cu 1+ states, signifying the beneficial role of Mn 3+ and Cu 2+ for facilitating OER. The ordered CMO structures containing lower Mn 3+ /Mn 4+ and Cu 2+ /Cu 1+ 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.