The Kinetic Study And Frist-principle Calculation Based On Photo-Thermochemical Cycle For CO₂ Reduction

With rapid development of industry and economic all over the world,lots of fossil fuels are consumed,which causes a lot of serious energy and environmental problems.Converting solar energy into solar fuel is a promising clean energy technology.At present,the methods of solar energy synthesis fuel include photothermal decomposition,photothermalchemical cycle,photocatalysis and photoelectrochemical.In order to enhace the utilization rate of solar energy,our research group proposed a novel method to decompose CO2,which is called photo-thermochemical cycle(PTC).The first step of the photothermal chemical cycle for CO2 reduction is to generate oxygen vacancy under light,and the second step is to generate CO which is generated by CO2 reacting with oxygen vacancy.There are three key questions of PTC:1 The generation and separation of photogenic electron hole pairs;2 Reaction of electron hole pairs with material to generate oxygen vacancy;3 Oxygen vacancy and CO2 reaction.Our research mainly focused on photothermal chemistry before,while the kinetic factors of the second step between oxygen vacancy and CO2 reaction were less concerned.It is very important to deeply study the thermal reaction dynamics to improve the design of materials and deepen the mechanism of reaction.In this paper,titanium dioxide films were produced using a sol-gel method and hydrothermal method and applied in the photo-thermochemical cycle(PTC)for CO2 reduction,compared with treated mixed crystal P25(PT)in the PTC.A comparison of CO production showed that PT performed better than ST and HT.Average CO production of PT was 2.33 ?mol/g,which was nearly 1.39 times to ST's CO production and 4.64 times to HT's CO production.PL experiment showed that the PT of mixed crystal structure electron hole was lower than that of the only crystal type ST,and ST is lower than HT which was low crystallization degree.The effect of electron hole separation on CO production was shown.The effect of heating time on CO yield was investigated by a series of PT materials.Combining with In-situ DRIFTS,the influence of thermal reaction kinetics on the circulation was further investigated.The CO2-intermediate group is present in In-situ DRIFTS,with which the mechanism of photothermal chemical cycle is further explored.Cu-loaded TiO2 material was prepared by photodeposition(CT),5 groups of photothermal chemical cycle experiments were carried out,and the CO yield of CT under 1h heating time was found to be 5.3 times of PT.XRD and TEM showed that CT and PT had similar type,and Cu was highly dispersed on the surface of TiO2 or into the lattice.UV-VIS showed that the band gap of CT was smaller than PT,which was consistent with the calculated electronic state density(DOS).PL showed that the fluorescence intensity of CT samples is less than PT,which was consistent of the DOS of Cu load which promote the separation of electron holes.The configuration of CO2 adsorption and CO adsorption on the surface was optimized respectively to obtain the second step reaction path.The results showed that the oxygen vacancy was the reactive center,and the Cu load promoted the CO2 adsorption and CO generation reaction.The cyclic experiment of different heating time was carried out by using CT material,and it was verified that the Cu loading increased the dynamic factors and promoted the circulation.