Abstract A multi-step mechanism is discussed for the oxidation of BH 4 − on Cu anode in NaOH solution. Polarization experiments are conducted in 2 M sodium hydroxide solutions with 0.5, 1.0, and 2.0 M NaBH 4 at 25, 50, and 75 °C, respectively. The rate-determining step is the electrochemical oxidation of B H 4 , ad − that reacted with O H ad − at low overpotentials and changes to the competitive adsorption of BH 4 − or OH − at higher overpotentials. The theoretical predictions are satisfactorily in accordance with the polarization data. However, these predictions deviate from the data at the highest temperature or concentration of BH 4 − because of the bubbling of the side product, H 2 .