Method and apparatus for water electrolysis, and method for determining drive potential of water electrolysis

A water electrolysis method comprising:

• supplying at least water into an electrolysis cell which includes a solid polymer electrolyte membrane, and an anode and a cathode disposed sandwiching the solid polymer electrolyte membrane therebetween;
• and
• providing a potential P between the anode and the cathode to generate oxygen from the anode, wherein
• an oxidation catalyst containing at least one of first transition metals is present on at least a part of a surface of the anode, and
• the potential P satisfies P1<P<P2,
• wherein P1 indicates a lowest potential at which oxygen is generated from the anode, and P2 indicates a lowest potential P2 at which a quantitative index of a dissolved chemical species derived from the oxidation catalyst begins to show potential dependence, and
• wherein said method further comprises, before providing said potential P between the anode and the cathode, determining said drive potential P by comparing a first curve and a second curve, the first curve having been formed by plotting the amount of oxygen evolution from the anode against a potential between the anode and the cathode, and the second curve having been formed by plotting a quantitative index of a dissolved chemical species derived from the oxidation catalyst against the potential between the anode and the cathode.