New Approach to Lowering of the Overvoltage for Oxygen Evolution on RuO2 and Related Metal-Oxide Electrodes by Ion Implantation

The ion implantation method is applied to the improvement of the oxygen-evolution activity for metal oxide electrodes. The implantation of metal ions such as Co^+, Zn^+, and Ru^+ into nanocrystalline RuO2 and RuxTi1-xO2 (x = 1/2 and 2/3) film electrodes caused negative shifts of current density (j) vs potential (U) curves for oxygen evolution by about 20-100 mV, indicating the lowering of the overvoltage for oxygen evolution. Detailed experiments have shown that the lowering of the overvoltage is neither due to a change in the chemical composition of the electrode surface nor due to an increase in the effective area of the electrode surface, but rather is due to production of certain crystal defects (such as atomic gaps) that can act as active sites for oxygen evolution. The result is of much interest, suggesting that the control of surface defect structures is a promising approach for the improvement of the oxygen evolution activity.