A simple route to electrophoretic deposition of transition metal-coated nickel oxide films for electrochemical capacitors

Nickel hydroxide films coated with transition metals such as nickel and cobalt were fabricated directly by a one-step electrophoretic deposition (EPD) in the presence of charging additives (transition metal salts). A nickel hydroxide particle with a weakly charged surface in an isopropanol solution was found to be detrimental to EPD and dispersion. When a small amount of charging additive was added to the suspension, the adsorption of dissolved metal ions on the nickel hydroxide resulted in a more positively charged particle surface, facilitating EPD and dispersion. When nickel hydroxide particles migrated to the negative electrode during the EPD process, the metal ions adsorbed on the particle were reduced electrochemically to form a metal layer. The as-deposited nickel hydroxide film converted to nickel oxide following heat treatment at 300 °C. Our results revealed that nickel oxide films coated with nickel and cobalt showed better capacitive behavior than the bare film. The improved capacitive behavior was attributed to the co-deposition of transition metals, which provided additional active sites on the nickel oxide surface for the electrochemical reaction to occur.