Co3-O4/NiO with abundant Ni3+ active sites for boosting oxygen evolution reaction

Electrocatalytic water splitting has received widespread attention. However, due to the slow reaction kinetics and complex electron transfer process, the oxygen evolution reaction (OER) occurring at the anode has become a bottleneck. Herein, the metal-defective Co3-xO4 was selected as the electron-acceptor carrier and Co3-xO4/NiO was synthesized by a simple two-step method. The results show that Co3-xO4/NiO has a low overpotential of 240 mV and 320 mV at 10 mA·cm−2 and 100 mA·cm−2, a low Tafel slope of 64 mV/dec, and the electrochemical surface area (ECSA) of Co3-xO4/NiO is as high as 1033.3 cm2. Moreover, the decrease in activity after the 60 h stability testing is negligible. Combining experiments and theoretical calculations, the high activity and stability of Co3-xO4/NiO is attributed to the tunable electronic structure, and more electrons are transferred from NiO to Co3-xO4 which leads to the in-situ generation of more Ni3+ as active sites. The Co3-xO4/NiO with abundant of Ni3+ can effectively regulate the oxygen-containing intermediates (OH*, O* and OOH*) with appropriate binding energy, reduce Gibbs free energy change of rate-limiting step, and accelerate OER reaction kinetics. This work provides an efficient strategy to generate and stabilize Ni3+ active sites and confirms the key catalytic role of Ni3+ in the OER process.