On the Potential of the Electrode of Ni|NiO|Aqueous Solution. (Significance of the Potential in the Anodic Formation of Oxide-films on Nickel, 1st Report)

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  • Ni|NiO|水溶液-電極の電位について
  • Ni NiO スイヨウエキ-デンキョク ノ デンイ ニ ツイテ

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Abstract

Changes of the chemical and the electrochemical potential of electrons and of ions at the phase boundaries and in each phases were discussed in the electrode of Ni/NiO/H2O. The equilibrium Galvani-potential g(Ni⁄NiO) at the phase boundary of Ni/NiO is given by g(Ni⁄NiO)=−[(Ni)μNi2+−(NiO)μNi2+]⁄2F since in equilibrium the electrochemical potentials of Ni2+ are equal in both phases of Ni and NiO. In the same way, g(NiO⁄H<SUB>2O)</SUB> is given by g(NiO⁄H<SUB>2O)</SUB>=−[(H<SUB>2O)</SUB>μH<SUB>2O</SUB>−(NiO)μO2−−2(H<SUB>2O)</SUB>μH+]⁄2F. Then, the Galvani-potential of Ni/NiO/H2O electrode can be written in the form of g(Ni⁄NiO)+g(NiO⁄H<SUB>2O)</SUB>=−[(Ni)μNi2++(H<SUB>2O)</SUB>μH<SUB>2O</SUB>−(NiO)μNiO−2(H<SUB>2O)</SUB>μH+]⁄2F which is represented by the equilibrium potential Ea of the redox reaction (a) Ni+H2O=NiO+2H++2θ, when refered to the normal hydrogen electrode. When the concentration of nickel ions in solution is lower than that corresponding to the solubility product of NiO, the spontaneous potential of a nickel electrode covered with pore-free NiO is slightly less noble than Ea because the Galvani-potential of g(NiO⁄H<SUB>2O)</SUB> changes to the less noble direction so as to keep a mixed potential of both cathodic and anodic reactions of O2−(NiO)+2H+(aq)→H2O and Ni2+(NiO)→Ni2+(aq). If the surface film of NiO is porous, the spontaneous petential changes to the less noble direction to a greater extent with increase of the area of active holes. When a constant anodic current i is supplied to the electrode of Ni/compact NiO/H2O, the potential difference EII should appear between the phase boundary of Ni/NiO and NiO/H2O to drive the nickel ions Ni2+(NiO) through the film.

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