Co³⁺-O-V⁴⁺ cluster in CoVOx nanorods for efficient and stable electrochemical oxygen evolution

The development of cost-efficient and long-term stable catalysts for the oxygen evolution reaction (OER) is crucial to produce clean and sustainable H₂ fuels from water. Here we demonstrate a cobalt vanadium oxide (CoVOx-300) working as such an efficient and durable electrocatalyst. Such an active catalyst is beneficial from the balanced Co³⁺-O-V⁴⁺ active species, which show the high surface Co³⁺ contents with matched V⁴⁺ generated by rapid heat treatment. The CoVOx-300 with highest Co³⁺/Co²⁺ ratio of 1.4 and corresponding highest V⁴⁺/ V⁵⁺ ratio of 1.7 exhibits remarkable OER activity with an overpotential of 330 mV at current density of 10 mA cm⁻² (η₁₀), a shallow Tafel slope of only 46 mV dec^-1 and a current density of 100 mA cm⁻² at an overpotential of 0.38 V vs RHE, which is 20 times higher than the active CoOx-300 and 1000 times higher than VOx-300. The catalyst also shows excellent stability for 10 h in alkaline media and a 40 % reduced activation energy to the counterpart, CoOx-300. The overpotential (η₁₀) of CoVOx-300 also shows nearly 70 and 80 mV lower than the corresponding CoOx-300 and CoVOx catalysts, respectively and 20 % lower Tafel slope than the commercial benchmark catalyst RuO₂. Thus, this study for the first time demonstrates that surface Co³⁺-O-V⁴⁺ species play a crucial role in improving electrocatalytic properties and stability for water oxidation reaction and the approaches allow the rational design and synthesis of other active transition metal oxides toward efficient OER activity.