Activity manifestation via architectural manipulation by cubic silica-derived Co3O4 electrocatalysts towards bifunctional oxygen electrode performance

Abstract

Electrocatalytic water splitting reaction utilizing non-renewable energy resources significantly leads to a sustainable energy infrastructure. Highly efficient bifunctional catalysts for oxygen reduction and oxygen evolution reactions (ORR/OER) are essential for the replacement of platinum, ruthenium and iridium metals. We used four different silica templates to create excellent mesoporous cobalt oxide (Co₃O₄) electrocatalysts in crystalline form. Various advanced techniques confirm the spinel structure composed of both Co³⁺ and Co²⁺ sites, which lead to an enhanced surface area, mesoporosity, and a rod morphology with a cubic-like network structure. Among these replicas, the Mobil composition of matter (MCM)-48-derived Co₃O₄ (Co₃O₄-M8) material demonstrates remarkable OER activity with an observed potential of 1.76 V, a Tafel slope of 107 mV dec⁻¹ and a lower charge transfer resistance. Such a high performance is observed due to assistance of the Co³⁺ to Co⁴⁺ transition during the oxygen evolution reaction. The ORR was more active on the Korea advanced institute of science and technology (KIT)-6-derived Co₃O₄ (Co₃O₄-K6) material, which displayed a more positive onset potential of 0.85 V, a half-wave potential of 0.56 V and a better current density in alkaline medium. In addition, we found that the stabilization of Co²⁺ active sites in the Co₃O₄-K6 material is the reason for the enhanced oxygen reduction reaction. The observed bifunctional activity (ΔE = E_OER@10 mA cm⁻² − ORR@E_1/2) for the Co₃O₄-K6 catalyst is 1.22 V, which shows significant performance among all the catalysts prepared in this work. Such an earth-abundant mesoporous Co₃O₄ catalyst obtained via an environmentally benign process is anticipated to revolutionize electrochemical energy conversion and storage devices.