The role of synthesis vis-à-vis the oxygen vacancies of Co3O4 in the oxygen evolution reaction

Abstract

The oxygen evolution reaction over oxide vacancy-induced spinel Co₃O₄ is a topic of tremendous scientific attention owing to the favourable adsorption of water, as also shown here through DFT calculations. However, the inclusion of an optimum amount of oxygen-ion vacancies at the surface and in the bulk of Co₃O₄ remains a synthetic challenge in order to enhance the efficacy of the oxygen evolution reaction. Here, we have attempted a single-step scalable approach of solution combustion synthesis to incorporate the oxide ion vacancies in high-surface-area Co₃O₄. To benchmark the catalyst, we also synthesized Co₃O₄ using elevated-temperature calcination routes. Detailed structural and surface analyses revealed the significant presence of oxide ion vacancies in the combustion-synthesized material. The solution combustion synthesized Co₃O₄ due to the presence of oxygen-ion vacancies exhibited an excellent oxygen evolution reactivity with a lower overpotential and higher current density compared with the other Co₃O₄ materials synthesized using calcination routes. Tafel slope calculations indicated that the formation of surface hydroxyl species through water dissociation over the oxide ion vacancies is the rate-determining step of the overall reaction. The mechanistic role of the oxygen-ion vacancies in the oxygen evolution reaction was further explored via DFT studies.