Homogeneous NaBH4-reduced Co3O4 thin film electrodes with enhanced oxygen evolution electrocatalysis were obtained via a controlled-synthesis route.Firstly CoOx colloids were synthesized via ethylene glycol solvothermal method and cast on conductive glass substrates.The oxygen evolution reaction (OER) electrocatalysis of these asprepared Co3O4 thin films were then significantly enhanced via a simple surface reduction by NaBH4 solution.The OER catalytic performance of the NaBH4-reduced thin films was strongly dependent on the NaBH4 concentration.The use of NaBH4-reduced thin film electrodes for OER in alkaline solution supported higher current density and consequently negative shifts of the onset potential compared to that of the pristine.The optimal B12.5,20-Co3O4 thin films exhibited excellent OER catalytic performances: At the current density of 10 mA·cm-2,a low overpotential of 365 mV and a small Tafel slope of 59.0 mY· dec-1 were observed.In addition,these B12.5.20-Co3O4 thin film electrodes possessed good stability that can well recover its OER performance in a 24-h chronoamperometric stability test.