Probing the active sites of Co3O4 for the acidic oxygen evolution reaction by modulating the Co2+/Co3+ ratio

Abstract

Exploring active and stable electrocatalysts for the acidic oxygen evolution reaction (OER) is necessary to broaden the practical applications of proton exchange membrane electrolyzers. Unfortunately, the active sites of electrocatalysts for the acidic OER, which are the most powerful tool for designing and optimizing OER electrocatalysts, still remain ambiguous. Herein, we synthesize Ag doped Co₃O₄ with different atomic ratios of Co²⁺/Co³⁺ and investigate the effect of preferential exposure of Co²⁺ in Co₃O₄ on the acidic OER through systematic experiments for the first time. X-ray photoelectron spectroscopy is used to probe the atomic ratio of Co²⁺/Co³⁺ on the surface of Co₃O₄. The results demonstrate that Co₃O₄ richer in Co²⁺ shows the best acidic OER performance, and affords a current density of 10 mA cm⁻² at an overpotential of 470 mV along with having a satisfactory stability in H₂SO₄ solution. Moreover, low-temperature calcination treatment is found to be an effective method to aid preferential growth of Co²⁺ on the surface of Co₃O₄, further making our synthesis process more practical and universal. Therefore, this work provides some insight into designing non-precious electrocatalysts for the acidic OER, by identifying active sites and offering a versatile modulation strategy on the preferential growth of real active sites.