AbstractThe reduction and the oxidation of hypophosphite on a Ni‐Ag electrode have been studied to provide the information about the phosphorus incorporation mechanisms during the electro‐less deposition and the electrodeposition of Ni‐P alloys. In the electrooxidation process, an absorbency band around 240 nm, which was ascribed to tbe formation of an intermediate PHO2, was observed by in situ UV‐Vis subtractive reflectance spectroscopy. Accordingly, the electrooxidation of hypophosphite might undergo an H abstraction of hypophosphite from the PH bond to form the phosphorus‐centred radical PHO2, which was subsequently electrooxidized to the final product, phosphite. In the reduction process Ni‐phosphine compound N‐(PH3), was observed byin situ surface Raman spectroscopy. The results from the Raman experiments show that, in the NiSO4‐free solution, hypophosphite was reduced only to Ni‐phosphine compound, while in the case where NiSO4 coexisted in tbe solutions, the Ni‐phosphine compound, as an intermediate, was oxidised by Ni2+ to elemental phosphorus in alloys with nickel acting as the catalyst.