Graphene Based Hybrid Structures For Solar-driven Water Splitting

Developing clean and renewable energy has been considered as one of the most effective ways to address the energy and environmental related crisis.One of the most powerful sustainable energy,solar energy,can be utilized through solar-driven water splitting,which contains two energy conversion units.One is the photovoltaic solar cell,which converts light energy to electric energy for power supply.The other is the water electrolysis unit,which converts electric energy to hydrogen energy by using highly efficient and stable catalysts.Graphene and its hybrid nanocomposites,with their excellent optical,electrical and mechanical properties,can be applied in this system,to further improve the photoelectric conversion efficiency,and decrease the electrical consumption in the water electrolysis module.In this thesis,to develop the solar-driven water splitting system,first,a hybrid graphene/Si-solid electrolyte solar cell is fabricated by combining graphene with solid electrolyte,achieving a conversion efficiency to be 11%,acting as the photoelectric conversion unit in this system.Then,water electrolysis catalysts are prepared by simply depositing transition metal based compounds on the conductive graphene substrate,which largely reduce the noble Pt consumption in hydrogen production,realizing the conversion of electric energy to hydrogen energy at low cost.By connecting the solar cell and water electrolysis unit,a solar-driven water splitting system is constructed,aiming at improving solar energy utilization.First,to develop the photoelectric conversion unit in this system,graphene woven fabric film(GWF),which facilitates solid electrolyte filling,is combined with Si to form a hybrid heterojunction and photoelectrochemical solar cell.The working mechanism of the solid electrolyte is systematically studied.The photoelectric conversion efficiency of this solar cell is 11%,which is suitable for solar water splitting.Second,to reduce noble metal consumption in designing water electrolysis catalysts,a graphene/Mo S2 hybrid structure is prepared,which demonstratesgood hydrogen production performance in acid electrolyte.To further improve the catalytic activity of this structure,Pt nanoparticles(Pt NPs)are loaded through a photo-promoted deposition approach,which is studied to unravel the underlying mechanism.Graphene/Mo S2-Pt NPs catalyst delivers negligible overpotential low to be 56 m V,with Mo S2 partly replacing Pt,acting as the cathode material in the water electrolysis unit,promoting the water splitting process.Finally,to prepare non-noble catalysts for overall water splitting,graphene is combined with transition metal(Co or Ni)selenides.A vertically-aligned nanoarray structure is obtained through morphological control.This hybrid structure acts as the cathode and anode catalyst simultaneously in the alkaline electrolyte for water electrolysis unit,which totally replace noble metal Pt.When further connected to the solar cell module,a non-noble solar-driven water splitting system is constructed,which possessed highly efficient and stable solar energy conversion ability with low cost.