Theoretical Calculation Study Of The Reaction Mechanism Of Photothermal Catalytic H₂O Splitting And CO₂ Reduction

The utilization of solar energy is an important part of the clean energy revolution in the future.Based on the utilization of solar light and heat,photothermal catalytic H₂O splitting and CO₂reduction to produce solar fuel is a sustainable energy conversion and utilization method,and it is an effective method to achieve hierarchical and efficient use of solar energy in the future.Density functional theory based on quantum mechanics provides practical ideas and methods to simulate the surface of materials and to explore microscopic reaction mechanisms at the molecular scale.Metal oxides are the most common catalytic materials.Preliminary screening of metal oxides based on theoretical calculations can effectively reduce experimental costs and improve experimental efficiency.In this work,the surface formation energy and oxygen vacancy(V_O)formation energy are used as the screening criteria to screen different surfaces of TiO₂,In₂O₃,CeO₂,ZnO,Zn₂GeO₄,GeO₂,WO₃,and ZrO₂.The results show that eight surfaces have the suitable surface formation energy and V_O formation energy,which indicates that these surfaces have a certain degree of stability and can also form more surface V_Os as reactive sites.Therefore,anatase TiO₂(101)surface and In₂O₃(110)surface are selected for subsequent calculation.During the photothermal catalytic H₂O splitting,the interaction between the surface of metal oxide and H₂O may cause lattice oxygen to participate in the reaction to form surface V_Os.V_Os as catalytic sites can affect the H₂O splitting reaction activity,and change the reaction pathway.Based on this,this work proposes two different reaction pathways for the photothermal catalytic H₂O splitting on the surface of metal oxide.Anatase TiO₂ and Fe/Cu-doped anatase TiO₂(101)surfaces are used to calculate the complete free energy profiles of the two different pathways,which reveal that H₂ evolution is the rate-determining step.More critically,the balance between the formation and reactivity of V_Os is the key factor for the pathway preference for H₂O splitting.And the doping of Fe and Cu promotes the formation of V_Os and enhances the electron transfer from H₂O to the surface,which can effectively promote H₂O splitting.The doping of Fe and Cu and V_O formation on a TiO₂ and Fe-a TiO₂ introduce defect energy levels into the band gap,which are conducive to the extension of light absorption and the separation of electron-hole pairs;this in contrast to V_Os on Cu-a TiO₂,which lead to the disappearance of impurity energy levels in the band gap.In addition,temperature is an important factor affecting the photothermal catalytic reactivity.The increase of temperature will promote H₂ evolution but inhibit H₂O adsorption.Therefore,the optimal experimental temperature can only be determined based on actual tests.Further,in order to explore the effect of surface V_Os on the photothermal catalytic H₂O splitting,the In₂O₃(110)surface is studied and the surface V_O formation ability is changed with Ti/Mn/Fe/Co/Ni/Cu/Zn doping.Surface V_Os on In₂O₃ are easier to form and can effectively promote H₂O dissociation adsorption and H₂ evolution.Metal doping has significant and different effects on H₂ evolution reactivity,which alters the reaction pathway for H₂O splitting.Based on the V_O formation energy and*H adsorption energy,the relation between surface V_O formation and the reactivity of surface V_Os reveals that surface V_Os with lower formation energies are more unfavorable for H₂ evolution.Therefore,surface V_Os play a key role in the reaction pathway preference and H₂O splitting catalytic activity.Metal doping significantly reduces the band gap,and facilitates the separation of photogenerated electrons and holes.The electron transfer from surface lattice oxygen to the doped metal is promoted,which makes it easier to form V_Os on the surface,but strengthens the interaction between*H and the surface,and hinders H₂ evolution on VO.Based on the preliminary exploration of H₂O splitting,further consideration is given to using H₂O as the hydrogen source to explore the pathway and mechanism of the photothermal catalytic CO₂ reduction.Anatase TiO₂(101)surface and its modified surface are studied.Through preliminary screening,MgO doping and Au loading can effectively enhance the CO₂ competitive adsorption capacity,promote the formation and adsorption activation of H*.In the photothermal catalytic CO₂ reduction,competition between desorption and reduction of the key intermediates(CO*,HCOOH*,HCHO*and CH₃OH*)plays an important role in the reaction pathway and product selectivity.The loading of Au and the doping of MgO enhance electron transfer between the key intermediates and the surface,as well as the internal electron transfer within the key intermediates,which efficiently activates the key intermediates.Therefore,the key intermediates all tend to be further reduced to form new intermediates to participate in the subsequent reaction,which effectively improves the selectivity of CH₄ products.The theoretical calculation of the reaction pathway and mechanism of photothermal catalysis of H₂O splitting and CO₂ reduction has been verified by the results of photo-thermochemical cycle experiments and photothermal catalysis experiments,which proves that the microscopic reaction pathway and mechanism proposed in this work are reasonable and scientific.This result indicates that theoretical calculation can be used to guide the screening and design of high-efficiency catalytic materials,as well as the directional design of photothermal catalysis experiments.