Hydrogen Production Using Different Graphene/Au@TiO2 Composites Under Visible and Ultraviolet Light

Abstract

In order to avoid serious environmental and economic damages from energy use, humans must stop using fossil fuels altogether, as soon as possible. One possible strategy to cut the dependence of fossil fuels and, at the same time create a new economic force, is to develop a hydrogen based energy economy. A potentially viable way forward is to produce H2 from water by combining solar energy and heterogeneous photocatalysts. For these reasons the objectives of this investigation were: 1) synthesize a high surface area TiO2 nanowires (NWs) catalyst in the rutile phase, 2) incorporate different amount of gold nanoparticles into the as-synthesized catalyst and into the commercial form of TiO2 (P-25) using a chemical reduction method, 3) incorporate graphene to the Au@TiO2 composites, 4) produce hydrogen via water splitting using visible and ultraviolet light. The hypotheses of the study were: a) The catalyst with the higher surface area will produce the highest amount of hydrogen, b) The gold nanoparticles will enhance the hydrogen production and will allow the use of visible light due to the surface plasmon resonance of the gold nanoparticles, c) The incorporation of graphene will enhance the hydrogen production since it will reduce the electron/hole recombination in all the Au@TiO2 composites. Interestingly, the incorporation of gold nanoparticles into the titania surface enhanced the surface area in both P25 and TiO2 NWs. The hydrogen production obtained by using Au@P25 catalysts was measured to be 800 μmolg-1h-1 under irradiation at 400 nm and 1,436 μmolg-1h-1 using Au@TiO2 NWs at the same wavelength. The incorporation of graphene enhanced the hydrogen production in both P25 and TiO2 NWs. A maximum hydrogen production of 978 μmolg-1h-1 and 1,689 μmolg-1h-1 was obtained for P25 and TiO2 NWs, respectively, after the incorporation of graphene. All the hypotheses were correct and all the objectives achieved. The characterization of the synthetized compounds were performed with: 1) X-ray diffraction (XRD), 2) Field emission Scanning Electron Microscopy (FESEM), 3) Brunauer, Emmett and Teller (BET), 4) Gas Chromatographer with a Thermal Conductive detector (GC-TCD) and 5) Ultra Violet Visible spectroscopy (UV-VIS). Future works will be focused on producing hydrogen via water splitting by incorporating gold nanoparticles and graphene on synthesized zinc oxide nanowires and nanoparticles. The results with the zinc oxide composites will be compared with those obtained by the TiO2 composites. The contribution of this investigation relies in finding new and clean ways to produce hydrogen via water splitting.