Durability enhancement and degradation of oxygen evolution anodes in seawater electrolysis for hydrogen production

▶ Oxygen evolution anode in seawater electrolysis for hydrogen production. ▶ Sn 1− x Ir x O 2 intermediate layer effective in preventing oxidation of titanium substrate. ▶ Unevenness of the intermediate layer is responsible for localized growth of titanium oxide bumps. ▶ Localized titanium oxide growth results in destruction of electrocatalyst. ▶ Exposure of intermediate layer active for chlorine formation to NaCl solution determines the life of anode. For the anode composed of electrocatalyst oxide, intermediate layer and titanium substrate, the substitution of a certain amount of iridium with tin in the IrO 2 intermediate layer was remarkably effective in elongating the life of the anode in preventing oxidation of the substrate titanium during oxygen evolution. The longest life was realized by preparation of intermediate layer with uniform thickness by brush-coating of H 2IrCl 6–SnCl 4 butanol solution and subsequent calcination. The anode with the intermediate layer prepared from 0.04 M H 2IrCl 6–0.06 M SnCl 4 butanol solution showed the best performance, that is, the oxygen evolution efficiency higher than 99.8% for more than 4300 h in the electrolysis of 0.5 M NaCl solution of pH 1 at the current density of 1000 Am −2. An increase in SnCl 4 concentration decreased the viscosity of the coating solution with a consequent enhancement of uniformity of the intermediate layer but decreased the thickness of the intermediate layer acting as a barrier to prevent oxidation of titanium. Thus, the best performance was attained at an intermediate SnCl 4 concentration. The growth of an oxide layer on titanium during electrolysis occurred and was found by the potential increase.