A Robust Bifunctional Electrocatalyst with Crystalline-Amorphous Interfaces toward Oxygen Reduction/Evolution Reactions

Abstract

This work reports the successful synthesis of a highly stable and durable non-PGM catalyst Co₃O₄/Co_xCe_1−xO_2−δ/C via a simple solvothermal process. The electrocatalytic ability of Co₃O₄/C, CeO₂/C and Co₃O₄/Co_xCe_1−xO_2−δ/C are tested for oxygen reduction and oxygen evolution reaction (ORR, OER). Under identical conditions, the electrochemical studies of the catalysts reveal enhanced performance of the Co₃O₄/Co_xCe_1−xO_2−δ/C. It shows the highest geometric current density (j_geo = ̶ 4.1 mAcm⁻² ) at 0.33 V vs. RHE. Moreover, Co₃O₄/Co_xCe_1−xO_2−δ/C has the earliest onset for OER with a bifunctionality index of ΔE = 1.05 V and has the highest turnover frequency. The catalyst was compared with benchmarks like 20 wt% Pt/C for ORR and RuO₂ for OER. Chronoamperometry studies (CA) reveals superior performance of Co₃O₄/Co_xCe_1−xO_2−δ/C over Pt/C for ORR and accelerated durability test (ADT) shows no observable shift of half-wave potential (E_1/2). This enhancement of electrocatalytic ability of Co₃O₄/Co_xCe_1−xO_2−δ/C are attributed to (1) higher degree of Co²⁺:Co³⁺ ratio (3.6) in Co₃O₄/Co_xCe_1−xO_2−δ/C than in Co₃O₄/C (0.8) as revealed from XPS. This is a result of doping of cobalt into CeO₂, and (2) presence of crystalline-amorphous interfaces as observed from HRTEM.