The electrocatalytic oxidation of hypophosphite on a nickel electrode has been studied by means of in situ UV-Vis subtractive reflectance spectroscopy to obtain information about the anodic oxidation mechanism. An absorbency band around 245 nm, which was ascribed to the formation of an intermediate, PHO - 2 , was observed in the electrocatalytic oxidation process. Accordingly, the electrocatalytic oxidation of hypophosphite might undergo a H abstraction of hypophosphite from the P-H bond to form the phosphorus-centered radical PHO - 2 , which is subsequently reacted with water to form the final product, phosphite.