Preparation Of High Efficient Photoelectrocatalysts And Its Application In Selective Reduction Reaction

With the greenhouse effect of CO₂ causing serious climate and environmental problems, CO₂ emission is now becoming a great global concern. Nevertheless, CO₂ is also a potential carbon resource to be better utilized for green energy production.With the advent of technology, especially the new technology of chemical synthesis,new type catalysts have been explored for achieving possible created new conditions for transfer CO₂ to chemical products. One of the ideal solutions to turn CO₂ problem to chemicals is to develop solar fuels by artificial photosynthesis, that is,storage of solar energy in chemical forms by photo-reducing CO₂ to high-energy compounds, such as methane, methanol, formic acid, urea, low carbon hydrocarbon,carbonate ester or even high-carbon based products. Such utility of CO₂ not only decreases the consumption of fossil fuel, but also remedy the environmental pollution.Recently, photoelectrocatalysis（PEC） supplies a successful conversion of CO₂ based on its high activities and drastically decreased necessary energy input. PEC reduction of CO₂ possesses a mild reaction condition（ordinary temperatures and pressures）, and it could meet the demand for high energy conversion by utilizing free and abundant solar energy. Such realization of transfer CO₂ resource to fuels was called “artificial photosynthesis”. The earliest report on photo-conversion of CO₂ was published by Halmann in 1978. Since that, TiO₂ has remained the most preferred photocatalyst and photoelectrocatalyst for CO₂ reduction. However, CO₂photo-conversion is still challenging the researchers for various reasons: poor stability of the catalysts, inefficient absorption of light, low quantum efficiency due to rapid e-/h+ recombination upon irradiation, facile backward redox reactions that lead to product dissociation and lack of product selectivity. Thus, we aim at designing and fabricating novel photoelectrocatalysts with high stability, high adsorption and high selectivity for overcoming the major shortcomings in the field of CO₂ reduction. Herein, Ti O₂ nanomaterials arrays prepared by different process were adjusted for widening the absorption spectrum to visible light or longer wavelength and increasing the capability for adsorbing and activating CO₂ molecules. The main research results include the following contents:1. MoS2/Ti O₂ NTs as cathode for H2 evolution via splitting waterSolvothermal route was proposed for the deposition of MoS2 nanoflakes wrapped around the TiO₂-nanotube arrays. Such hybrid MoS2/TiO₂ nanotube arrays electrode could serve as an excellent cathode for driving the H2 evolution reaction owing to the super H2 evolution performance of MoS2 and super-fast electron transfer rate of TiO₂ nanotubes.2. Photoelectrocatalysis driving carbon dioxide conversion into derivatives organic carbonates on Cu@MoS2/TiO₂ cathodeAn electro-deposition effect assisted ion-exchange method was proposed for coating cooper（Cu） nanoparticles on MoS2/TiO₂ nanotube arrays（MoS2/TiO₂-NTAs）.Such hybrid electrode showed both high specific surface area of TiO₂-NTAs and effective CO₂ activation property in the photoelectrocatalysis reaction system. Base on the above merits, a PEC driven simultaneous CO₂ reduction and degradation of organic pollutant system was proposed in this chapter. It is suitable for the industry application and environment requirement. In the present PEC reaction system, CO₂ molecules react with methanol for generating dimethyl carbonate（DMC） with high selectivity under light irradiation. The effect of the size and coverage of Cu nanoparticles on the PEC activities were mainly discussed. Meanwhile, the simultaneous effect between degradation of organic pollutant and CO₂ reduction was investigated the PEC system.3. The research of CO₂ reduction and carbon balance by using a UIO66-NH2-ZnO-Ni foam（cathode）/TiO₂ –NTs（anode） PEC systemZnO nanosheets were coated on the Ni foams by using an electro-deposition route. UIO66-NH2 was further grafted on ZnO nanosheets via solvothermal method owing to the strong bridge-bond effect between –NH2 and ZnO. Such UIO66-NH2-ZnO-Ni foam could serve as excellent cathode for driving the CO₂ PEC reduction owing to its strong CO₂ adsorption. Both the PEC performance for CO₂ reduction and the carbon balanced before and after the reaction were detailed investigated for better illustrating the working mechanism of the UIO66-NH2-ZnO-Ni foam（cathode）/TiO₂ –NTs（anode） PEC system.