Studies of surface composition and electrocatalytic activity of titanium cathodes implanted with Ni +

Abstract

A cathode with the function of releasing hydrogen was prepared by an ion implantation technique in which titanium was used as a substrate and Ni + as implanting ions. Three kinds of specimens were made: specimen 4 was implanted with 2.2 × 10 16 Ni + cm -2 at 50 keV; specimen 5 was implanted under the same conditions as specimen 4 but annealed at 200 °C for 1 h; specimen 6 was implanted with 1.5 × 10 16 Ni + cm -2 at 50 keV plus 7 × 10 15 Ni + cm -2 at 20 keV. The surface composition and chemical bonding of the implanted specimens were investigated by Auger electron spectroscopy and X-ray photoelectron spectroscopy. Furthermore, the electrocatalytic activity of the specimens was evaluated by measuring the exchangeable current density, Tafel slope and hydrogen overpotential. It was shown that (1) the concentration of nickel is almost constant throughout the whole surface layer of specimen 6, (2) the concentrations of nickel in the outmost zones increase in the order of specimens 4, 5 and 6, (3) the surface layers of the implanted specimens are composed of titanium, nickel, metallic compounds, oxide and carbide, and (4) a significant improvement in electrocatalytic activity is obtained, compared with the unimplanted specimen.