Electrochemical CO2-reduction to Formate over Activated Carbon-Supported Transition Metals (M = Cu, Fe, Zn, Ni, Co)-based High-Entropy Oxide

Abstract The electrochemical CO₂-reduction to produce valuable chemicals is a viable approach for mitigating carbon emissions. In this study, a high-entropy oxides (HEOs)-based electrocatalyst comprising the oxide of transition metals (M = Co, Fe, Zn, Ni, and Cu; termed CFZNC) anchored on activated-carbon powder (ACP) is synthesized by the polymerization of phenol and formaldehyde in situ dispersed with the respective metal salts, followed by ball milling and thermal treatment (carbonization and steam-activation) of the synthesized polymeric beads. The electrochemical characterization tests of the prepared CFZNC-HEO/ACP electrocatalyst confirm a high current density of 10 mA.cm⁻ ² at low applied-potential of − 0.37 V vs RHE, The electrochemical CO₂-reduction tests reveal the formate (HCOO⁻) Faradaic efficiency of ~ 98% and cathodic energy efficiency of ~ 62% at − 0.4 V, thus highlighting an efficient energy utilization of the material and selectivity towards formate production. Notably, the comparative tests reveal CFZNC-HEO/ACP outperforming its high-entropy alloy (HEA) counterpart, viz. CFZNC-HEA/ACP-based electrocatalyst, thus obviating the need of the high temperature hydrogen-reduction step required to transform metal oxides to metal alloy. The enhanced performance is attributed to the synergistic effect of the multiple metal oxides in the high-entropy formation, and the highly porous and conductive carbon substrate. These findings demonstrate the promise of the high-entropy metal oxides-based electrocatalyst in advancing efficient and sustainable CO₂ reduction technologies.