Preparation And Photoelectrochemical Performance For Water Splitting Of Oxide-Based Nanoarrays

With the depletion of fossil fuels?coal,natural gas and oil?,the development of new energy sources with sustainable supply is particularly important.The conversion of solar energy into chemical energy stored in the form of hydrogen,methanol,methane,etc.is considered to be one of the most promising strategies for solving future energy and environmental problems.Hydrogen has a high energy density per unit and does not produce greenhouse gases during combustion.Therefore,storing solar energy in the form of hydrogen is one of the most ideal ways to develop clean and sustainable energy.Extensive research has been conducted on photoelectrochemical water splitting reactions involving photocatalytic or photoelectrochemical?PEC?reactions that split water into H₂ and O₂.TiO₂ is one of the earliest researched n-type semiconductor photocatalysts and has been widely used in environmental purification,H₂ production,photosynthesis,CO₂ reduction,organic synthesis,solar cells,etc.The characteristics of nanomaterials are usually different from bulk materials.Modification of the surface of nanomaterials can provide a more favorable physical and chemical environment for chemical reactions to occur.The larger specific surface area of the nanostructured photoelectrode is beneficial to increase the contact area with the electrolyte and promote the chemical reaction on the photoelectrode surface.Modifying the energy band structure of the TiO₂photoelectrode with a narrow band gap nanomaterial will make the water decomposition reaction easier and easier.Narrow band gap materials?such as metal chalcogenides?have strong photosensitivity and can absorb a wide range of sunlight.However,long-term solar radiation will deactivate the photosensitizer material by self-oxidation,which limits the conversion efficiency and service life of the photoelectrode.To this end,we construct a ternary hybrid composite photoelectrode,modify the oxygen evolution promoter on the surface of the heterojunction photoelectrode,accelerate the rate of water decomposition reaction and improve the stability of the photoelectrode.In this paper,we constructed TiO₂/CdSe/Co-Pi,TiO₂/SnS₂/CoO_x and Au nanostructure modified three-dimensional TiO₂ nanorod array composite photoelectrodes to achieve efficient and stable PEC performance of photoelectrodes.The main contents of this paper are as follows:1.Constructed a ternary hybrid photoelectrode Ti O₂/CdSe/Co-Pi nanowire array for photocatalytic water splitting applications.The photoelectrochemical performance of the TiO₂/CdSe/Co-Pi photoelectrode is significantly enhanced than that of the TiO2/CdSe electrode without pure Co-Pi catalyst and the pure TiO₂ electrode.The photoelectric conversion efficiency of TiO₂/CdSe/Co-Pi and TiO₂/CdSe nanowire array photoelectrodes is about 3.3 times and 2.1 times higher than that of pure TiO₂photoelectrodes,respectively.The recombination of TiO₂ and CdSe and the electrodeposition of Co-Pi promoter accelerate the effective separation and transfer of photogenerated carriers.When the reaction continued for one hour,the photocurrent of the TiO₂/CdSe/Co-Pi nanowire array photoelectrode decreased by about 10%,and the photoelectrode showed good stability.2.Constructed a new two-dimensional structure heterojunction TiO₂/SnS₂/CoO_x nanosheet array photoelectrode for photoelectrochemical water splitting.The ternary hybrid nanosheet array photoelectrode shows a significantly enhanced photocurrent density.The photoelectric conversion efficiency of TiO₂/SnS₂/CoO_x is 1.8 times and3.6 times that of TiO₂/SnS₂ and pure TiO₂ photoelectrodes,respectively.The type II heterojunction constructed between TiO₂ nanosheets and layered SnS₂ improves the light absorption capacity and reduces the recombination of photogenerated carriers.The CoO_x catalyst further accelerates the oxidation kinetics of the water decomposition reaction,effectively promotes charge separation and improves the photoelectrochemical stability.3.A three-dimensional TiO₂ nanorod array loaded with Au nanostructures is constructed and used as the photoelectrode of the photoelectrochemical water splitting reaction system.A dendritic TiO₂ nanorod array was prepared on a conductive glass substrate by a two-step hydrothermal method,and then plasmon gold nanoparticles and gold nanorods were modified on the surface of the three-dimensional TiO₂nanorod array.Au nanostructure-modified three-dimensional dendritic Ti O₂ nanorod array photoelectrodes showed high photoactivity in the entire ultraviolet and visible range.Under simulated sunlight,the gold nanostructure modified TiO₂ nanorod array photoelectrode achieved higher photoelectrochemical performance.The highest efficiency of Au nanoparticle/Au nanorod modified three-dimensional dendritic TiO₂nanorod array photoelectrode is 0.75%,which is about 2.6 times higher than that of pure three-dimensional dendritic TiO₂ nanorod array.This enhanced performance is attributed to the improvement of light absorption capacity and carrier transmission efficiency through the plasmon effect of gold nanostructures and the reduction of electron-hole pair recombination.