Abstract
Anodic oxidation of sodium hypophosphite on smooth Pd and Pd/Pt electrodes and a Pd membrane is studied. Thei vs.E curves for the Pd electrode exhibit two anodic current peaks. One is caused by oxidation of H2PO 2 - , and the other, by simultaneous ionization of Pd and oxidation of H2PO 2 - . The hypophosphite ion adsorbed on the Pd surface hinders the formation of the passive film. This brings about a rapid dissolution of Pd in the oxygen region and its subsequent deposition with the formation of palladium black. The oxidation probably includes a slow heterogeneous chemical reaction, specifically, a cleavage of the P-H bond of the hypophosphite ion. The change in the reaction stoichiometry following an increase in solution pH and in anodic polarization is probably due to changing conditions of the H2PO 2 - adsorption and the number of adsorption sites occupied by H2PO 2 - on the surface. Following an increase in polarization, the phosphite ion may undergo oxidation to phosphate.
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