The anodic polarization curve of the oxygen electrode was examined on nickel in sulphate solutions of various pH values ranging from 0 to 14. It was found that oxygen evolution proceeds in accordance with two different reaction kinetics depending upon the pH value of the solution and the magnitude of the anode current density.
In acid solution and in alkaline solution in a relatively high current-density region, the anodic oxidation of water molecule through the rate-determining step HnO + OH(ads) -l-H+ + e is suggested as the reaction mechanism. In alkaline solution in a relatively low current-density region , the oxygen is evolved from OH-ion according probably to OH-+ OH(ads) + e, OH( ) + OH--+ O(ads) + Ha0 + e, and 20(ads) + Oe, with the second step determining the over-all reaction rate. The transition between oxygen evolution from Ha0 and that from OH-ion comes about at pH around 11 and is caused by the limiting diffusion current of OH-ion. Resume-Etablissement de courbes de polarisation anodique dune electrode ii oxygene, realisee par Ni dans NiSOp en solution aqueuse de divers pH entre 0 et 14. L'evolution d'oxygene denote deux reactions electrochimiques globales, dont les avancements respectifs dependent du pH et de la densite du courant anodique. En solution acide ou alcaline, dam un champ etendu de densite de courant, p&ape regulatricc parait btre He0 -+ (OH)(ads) + H+ + e-. En solution alcaline, a faible densite de courant, l'oxygene gazeux proviendrait principalement du m&anisme OH-+ (OH)(ads) + e-; (OH)(ads) + OH-+ O(ads) + Hz0 -t e-; 20(ads) -+ Op. Le pH de transition entre la predominance du premier mode (a partir de HaO) et celle du second (a partir de OH-) se situe alors vers