The electrode potential of the nickel oxide electrode has been determined as a function of water and solute activity in aqueous solutions of potassium hydroxide. The electrode, which was charged to a mean state of oxidation corresponding to 50% Ni II and 50% Ni III, was examined after long periods of time and by cathodic and anodic e.m.f. decay measurements after polarization in order to establish the quasi-reversible potentials by two methods. The results are discussed in terms of the stoichiometry of the potential-determining reaction, and distinction between mixed and true reversible potentials is made.
