Catalytic growth of CNTs and carbon onions by chemical vapor deposition on nickel-silica nanocomposite and its electrochemical catalytic study towards OER

Abstract

Novel carbon nanostructures are desired to develop alternative to noble metals like Iridium or Ruthenium based electrocatalysts as an anode material in alkaline water electrolyser. In this work first nickel-silica nanocomposite with a particles size of about 20 nm has been formed by alcogel electrolysis and then employed for catalytic growth of carbon nanostructures by CVD at 650–750 °C using alcohol precursor diluted by argon followed by electrocatalytic study towards oxygen evolution reaction (OER) in 1 M KOH solution. The carbon nanotubes of two different diameters, i.e. 10–30 nm and about 100–300 nm are seen at synthesis temperature of 650 °C. The larger tubes are replaced by irregular structures and carbon onions at 750 °C, with almost negligible nanotubes at the latter temperature. The diameter distribution of onion like carbon is found to be in the range 50–700 nm. Shift from thicker nanotubes to onions may be partly attributable to higher diffusion rates of carbon that result in complete coverage of larger nanoparticles without allowing an open end to continue the growth of a nanotubes. The small radius of curvature and extra-ordinary distortion required for carbon onions has not allowed them to grow on small nanoparticles. Moreover, our synthesized CNTs exhibited overpotentials of 354 mV at current density of 10 mA/cm2 which was 24 mV lower than revealed for carbon onions under similar conditions.