Controllable Preparation Of Single Metal Site Catalyst And Properties Of CO₂ Photoreduction And Electro Reduction

Unprecedented consumption of fossil fuels emits excessive amount of carbon dioxide(CO2),which causes a series of environmental problems such as global warming and ecological imbalance.Photochemical or electrochemical reduction of CO2 into hydrocarbon fuel molecules is of great strategic significance to alleviate the environmental pollution and serious energy shortage problem.However,the current CO2 reduction system is still hard to solve the above problems.As is well-known,CO2 reduction reaction is competitive with hydrogen evolution reaction,which results in low efficiency for CO2 redution.Moreover,the C-O bond cleavage,C-H,C-C coupling happened in CO2 redution process is too complex,and it is difficult to regulate their slow kinetic process.So far,preparing photocatalytic or CO2 electrocatalytic reduction materials with high activity,high selectivity and easy mass production is still a tough problem.Therefore,this paper uses single metal site catalysts as the basis of materials,by constructing an ideal structural model to explain the structure-activity relationship.The research contents of this paper are listed in the following paragraph:1.Atomically dispersed Sn?+Sites achieved efficient and robust CO2 electroreduction:Taking the low-cost metal Sn as an example,kilogram-scale single-atom Sn?+ atoms on N-doped graphene were first successfully fabricated by a quick freeze-vacuum drying-calcination method.HAADF-STEM image and synchrotron-radiation XAFS spectra revealed the atomically dispersed Sn atoms had slightly positive charges,which helped to stabilize CO2·-*and HCOO-*and hence enabled CO2 activation and protonation to proceed spontaneously,verified by in-situ FTIR spectra and Gibbs free energy calculations.In addition,the doped nitrogen atoms favored the rate-limiting formate desorption step through weakening the bonding strength between Sn and HCOO-*,affirmed by their elongated bond length and decreased desorption energy from 2.16 to 1.01 eV.As an outcome,the single-atom Sn?+on N-doped graphene exhibited a very low onset overpotential down to 60 mV.Also,thanks to the low overpotential and 100%Sn atom utilization,the single-atom Sn?+ on N-doped graphene achieved a new record of TOF up to 11930 h-1 for formate formation.Besides,the single-atom Sn?+ on N-doped graphene had unchanged current density and Faradaic efficiency during 200 h electrocatalysis.Briefly,this work offers a new pathway for substantially accelerating the electrocatalytic properties.2.Atomically dispersed Ag sites on titanate nanosheets realized improved visible-light-driven CO2 photoreduction:Taking the precious metal silver as an example,we first prepared single-site Ag anchored on ultrathin titanate nanosheets.Based on the theoretical calculations,we found that single-site Ag anchored on ultrathin titanate nanosheets had a significantly localized charge distribution,which benefited to CO2 adsorption and activation.Besides,single-site Ag anchored on ultrathin titanate nanosheets sample has increased visible light absorption and higher charge separation efficiency,thus bringing better CO2 visible light reduction performance.As a result,single-site Ag anchored on ultrathin titanate nanosheets can achieve a yiled of 37 ?mol g-1 h-1 for methanol under visible light,and the corresponding turnover number and turnover frequency is 120 and 20 h-1 respectively.Moreover,the selectivity of single-site Ag anchored on ultrathin titanate nanosheets catalyst can reach 90%.Furthermore,after 96 h long-time catalysis,the methanol yield and selectivity had no obvious decrease,which showed a superior CO2 photoreduction efficiency and high selectivity.This work provides a new idea for CO2 photoreduction.3.Single-site Co-doped titanate nanosheets catalyzed selective visible-light-driven CO2 photoreduction:Taking the metal Co as an example,we first prepared single-site Co doped ultrathin titanate nanosheets.Based on theoretical calculations,we found that single-site Co doped ultrathin titanate nanosheets had a significantly localized charge distribution,which benefited to CO2 adsorption and activation.Besides,single-site Co doped ultrathin titanate nanosheets sample has increased visible light absorption and higher charge separation efficiency,thus bringing better CO2 visible light reduction performance.As a result,single-site Co doped ultrathin titanate nanosheets achieved a yiled of 90 ?mol g1 h-1 for methanol under visible light.Moreover,the selectivity of single-site Ag anchored on ultrathin titanate nanosheets catalyst can reach 95%.Furthermore,after 96 h long-time catalysis,the methanol yield and selectivity had no obvious decrease,which showed a superior CO2 photoreduction efficiency and high selectivity.This work provides a new idea for CO2 photoreduction.