Radiation‐electrochemistry of the colloidal gold micro‐electrode: Hydrogen formation by organic free radicals

Abstract

AbstractVarious organic free radicals as well as Ni+ ions produce hydrogen in the presence of some 10−4 M of colloidal gold. The gold catalyst was prepared via the reduction of HAuCl4 either thermally by citrate or by y‐irradiation. The organic radicals were radiolytically produced. The mechanism of H2 formation includes electron transfer from the organic radicals to the gold particles, storage of a large number of electrons per gold particle, conversion of the electrons into adsorbed H‐atoms and desorption of the latter to form H2. — The rates of some of these steps were measured using the method of pulse radiolysis. 1‐Hydroxy‐1‐methyl ethyl radicals, (CH3)2COH, react with colloidal gold particles almost diffusion controlled provided that the gold particles are not charged with excess electrons. Charged gold particles react at a substantially lower rate. The stored electrons live seconds or even minutes depending on their number per gold particle. In the stationary state, up to 0.38 Coulomb of electrons could be stored per liter of a 2.9 · 10−4 molar gold solution, each gold particle carrying about 39 electrons. A comparison is also made between the catalytic activities of colloidal gold and silver. Due to the relative fast conversion of electrons into adsorbed H‐atoms, colloidal gold has less capacity for the storage of electrons than colloidal silver. — The dependence of the hydrogen yield on the pH of the solution, the concentration of gold, the size of the gold particles, the concentration of the polyvinyl alcohol stabilizer, and the intensity of radiation was also investigated. At high intensities, some of the radicals are destroyed in a gold catalysed disproportionation.