Abstract
Three kinds of oxides which are supposed to be NiO, Ni3O4 and Ni2O3, were found on the surface of nickel anode in alkaline solution by means of an electrochemical technique. It was estimated in 1 n KOH solution that the reversible potentials of transformation of NiO into Ni3O4 and of Ni3O4 into Ni2O3 were −0.35 V and +0.55 V, respectively. The potential of +0.55 V is fairly close to the value of +0.48 V reported by previous workers as the formation potential of Ni2O3. The potential of −0.35 V, however, is considerably different from +0.07 V reported by Glemser-Einerhand as the transition potential between NiO and Ni3O4. From the results of the experiment on the effect of dissolved oxygen in solution, it became clear that the potential of +0.07 V was not the equilibrium potential but the mixed potential of the dissolution reaction of nickel oxide and the reduction of oxygen. The free energies of the formation of Ni3O4 and Ni2O3 calculated from the equilibrium potentials were −189.7±∼1 and −124.2±∼1 kcal, respectively.
