Surface Wettability Regulation Of Indium-based Catalysts And Study On The Electrical Reduction Properties Of Carbon Dioxide

The excessive use of fossil fuels has emitted a large amount of CO₂,resulting in a series of environmental problems such as global warming and ocean acidification.Therefore,researchers have developed a variety of technical methods（such as electrocatalysis,photocatalysis,and biocatalysis）to reduce the concentration of CO₂ in the atmosphere while converting it into other more valuable chemicals.Electrocatalytic CO₂ reduction has the advantages of mild reaction conditions and controllable reaction parameters,which is one of the effective ways to realize the conversion and utilization of CO₂.However,the high chemical stability of CO₂ molecules(C=O bond energy up to 810 KJ mol^-1)and low solubility in water inhibit the rate of CO₂ reduction reaction（CO₂RR）.At the same time,high overpotential in the electrocatalysis process will cause violent hydrogen evolution reaction（HER）,which greatly reduces the current efficiency of CO₂RR.The electrocatalyst can reduce the energy barrier of the reaction and improve the reaction rate and selectivity of the reaction.Therefore,the preparation of efficient and stable CO₂RR electrocatalysts are particularly important for the practical application of CO₂RRAt present,noble metal,non-noble metal and carbon-based catalysts were developed and their CO₂RR properties were investigated.Indium-based catalysts as a class of non-noble metal-based catalysts have the advantages of low toxicity,low cost and catalytic CO₂ reduction to produce HCOOH,which has attracted wide attention.At present,various regulatory strategies have been developed to improve the CO₂RR performance of indium-based catalysts,such as size and morphology control,defect control,and heterogeneous structure construction.The surface wettability regulation of catalysts can optimize the microenvironment at the interface between catalysts,reactants and solvents,thus improving the catalytic reaction rate and selectivity.This regulation strategy has been used in many catalytic reactions in recent years（such as electrocatalytic oxygen/nitrogen reduction,photocatalytic CO₂ reduction）.However,the development of surface wettability control measures for indium-based catalysts and their effects on the performance of electrocatalytic CO₂RR are limited.Based on this,in this dissertation,an oxide of indium-based catalyst（In₂O₃）was used as the model catalyst,and two kinds of surface wettability regulation methods of In₂O₃ were developed.The influence of surface wettability on the CO₂RR performance of In₂O₃ was explored,and the internal mechanism of surface wettability regulation enhancing the performance of CO₂RR was further revealed.The main research contents are as follows:1.Porous fluoropolymer coating was constructed on the surface of In₂O₃electrode by a simple"drip coating"method.Electrocatalytic CO₂RR performance test showed that at-0.67 V vs.RHE,the In₂O₃ electrode without modified porous fluoropolymer coating had a Faraday efficiency of 24.1%for H₂ and 62.7%for HCOOH.After modification of fluoropolymer（polyvinylidene fluoride PVDF as an example）,HER on In₂O₃ electrode was significantly inhibited(FE_H2 was as low as 5.7%at the same voltage),and correspondingly FE_HCOOH was greatly increased（～82.3%）.The stability test showed that In₂O₃-PVDF electrode was obviously better than the In₂O₃electrode.The contact angle tests showed that the In₂O₃ electrode was hydrophilic,while the fluoropolymer coating increased the hydrophobicity of the electrode,and the carbon dioxide bubble contact angle proved that the modified electrode was aerophilic.The ab initio molecular dynamics（AIMD）simulation further showed that the modification of the fluoropolymer reduced the number of water molecules on the electrode surface.Therefore,competitive hydrogen evolution side reaction can be suppressed.Fluoropolymer as an"aerophilic sponge"can increase the local concentration of CO₂ near the active site of In₂O₃ on the electrode surface,forming rich gas-liquid-solid three-phase interfaces,which promoted the reduction of CO₂ and inhibited the competitive reaction of HER.In addition,density functional theory（DFT）calculation proved that the modification of fluorophenic polymer coating reduced the energy barrier of of the reaction path of CO₂ reduction to HCOOH and was not conducive to the adsorption of*H,so the CO₂RR performance of In₂O₃ catalyst was improved and HER was inhibited.2.In order to further improve the the activity of CO₂ reduction and stability of the In₂O₃ catalyst,alkyl phosphoric acid molecules with different alkyl chain lengths(C₁₈H₃₉O₃P～ODP,C₁₂H₂₇O₃P～DDP and C₆H₁₅O₃P～HXP)were grafted to the surface of In₂O₃ by P-O-In bond.By Fourier transform infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）and energy dispersive spectrometer（EDS）,it was proved that alkyl phosphoric acid molecules were successfully modified on the surface of In₂O₃.The contact angle tests showd that the longer the alkyl chain length,the larger the contact angle of the electrode,and the carbon dioxide bubble contact angle tests showed that the alkyl phosphoric acid functionalized In₂O₃ electrodes were aerophilic.The electrochemical performance test results showed that the modification of alkyl phosphoric acid molecules greatly inhibited the hydrogen production of In₂O₃catalyst(taking In₂O₃-ODP as an example,FE_H2 was as low as 6.6%at-0.67V vs.RHE,while FE_H2 of In₂O₃ electrode was 24.0%),and increased the faraday efficiency of HCOOH(at the same voltage,the FE_HCOOH of In₂O₃-ODP was 86.5%and the FE_HCOOH of In₂O₃ was 63.1%).At the same time,the longer the alkyl chain,the more obvious the hydrogen inhibition effect.Through AIMD simulation,it was proved that the modified electrodes with hydrophobic organic molecules were all in a state of hydrophobic and aerophilic,which can reduce the number of water molecules near the active site and increase the number of CO₂ molecules,thus inhibiting the hydrogen evolution side reaction and promoting the CO₂RR.