An ESR study of the electrocatalytic oxidation of hypophosphite on a nickel electrode
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The electrocatalytic oxidation of hypophosphite on a nickel electrode has been studied by means of electron spin resonance spectroscopy (ESR) to obtain information about the anodic oxidation mechanism. A 16-line ESR spectrum was observed in the process of the electrocatalytic oxidation of hypophosphite when spin trap alpha-pyridyl-N-tert-butyl nitrone (PBN) was added in the electrolytic solution. The spectra-line patterns and hyperfine coupling parameters were greatly consistent with those in the solution composed of Ti3+ (0.01 mol/l) + H2O2 (0.05 mol/l) + H2PO2- (0.01 mol/l) + PBN, in which reactions Ti3+ + H2O2 -->Ti4+ + .OH + OH- and .OH + H2PO2- --> .PHO2- + H2O take place and .PHO2- from the reactions formed spin adduct with PBN. Therefore, the spin adducts formed in the process of electrocatalytic oxidation of hypophosphite could be ascribed to an adduct belonging to .PHO2- and PBN. Accordingly, the electrocatalytic oxidation of hypophosphite might undergo an H abstraction of hypophosphite from the P-H bond to form the phosphorus-centered radical .PHO2-, which is subsequently reacted with water to form the final product, phosphite. (C) 2002 Published by Elsevier Science B.V.