Tuning Co2+ active sites over Co3O4 for boosting electrocatalytic oxygen evolution in neutral media

Electrochemical water splitting is a promising hydrogen production technology, with the oxygen evolution reaction (OER) as the key step. This study focuses on enhancing the OER activity under neutral conditions using acid-treated Co₃O₄ (A-Co₃O₄) as a viable alternative to noble metal electrocatalysts. We synthesized acid-treated Co₃O₄ with a tunable Co²⁺/Co³⁺ atomic ratio from 0.63 to 1.69. The A-Co₃O₄ exhibited an overpotential of only 438 mV at a current density of 10 mA cm^–2 with sustained activity for over 70 h. In-situ Raman spectroscopy analysis indicated that Co²⁺ sites were conducive to forming highly oxidative γ-CoOOH and stabilizing the CoOOH phase under OER conditions. Density functional theory (DFT) calculations showed that Co²⁺ sites on the surface of Co₃O₄ significantly lower the Gibbs free energy barrier of the rate-determining step compared to Co³⁺ sites. This study proposes a simple and effective acid-treatment method to enhance the OER activity of Co₃O₄, paving the way for its application in neutral seawater electrolysis and contributing to the development of cost-effective hydrogen production technologies.