Preparation And Electrocatalytic Performance Of Indium-Based Chalcogenide Compounds For Carbon Dioxide Reduction

The electrocatalytic reduction of CO₂ to chemicals that can be used in daily production using renewable energy sources such as geothermal energy,wind energy,tidal energy,and solar energy is a feasible strategy to reduce the content of major greenhouse gases and achieve a carbon-neutral energy cycle.Among the many electrochemical reduction products of carbon dioxide,formate（or formic acid）is one of the most important chemical intermediates in chemical industrial production,and is used in rubber,medicine,agriculture,environmental protection,leather,fuel cells,electrolysis Hydrogen has a wide range of applications in other fields,and the demand for formic acid at home and abroad has been increasing in recent years.Formic acid is mainly obtained by carbonylation of methanol and subsequent hydrolysis of methyl formate in chemical chemical production.However,this method of production is highly energy-dependent,and suffers from low reaction rates,unfavorable by-products and high costs.Therefore,the production of formic acid（or formate）chemical products by electrochemical CO₂ reduction technology is currently the most practical solution.Among many metal-based catalysts,indium-based catalysts have been widely studied due to their non-toxicity,non-polluting,low price and high selectivity for formic acid（or formate）.However,the efficiency and stability of In-based catalysts for electrocatalytic CO₂ reduction to formate are still poor at low potential and high current density.Therefore,it is a need to design and develop electrochemical carbon dioxide reduction catalysts with high catalytic activity,high target product selectivity,and durability.In this paper,indium-based chalcogenide nanomaterials were successfully prepared by chemical and electrochemical selective phase etching methods,and their electrochemical carbon dioxide reduction formate production performance was improved through morphology control and defect introduction strategies.In addition,the in-situ electrochemical Raman spectroscopy test and characterization method revealed the reaction mechanism and route of CO₂ reduction to formate by indium-based chalcogenide catalysts.The main research contents are as follows:1.According to the principle of binary phase diagram,a new type of nanorod indium sulfide compound（InS NRs）catalyst was successfully prepared by mixing In and S in a certain proportion reasonably by single-roll melt spinning and chemical selective phase etching.Through the analysis of electrochemical test results,InS NRs catalyst has excellent electrochemical carbon dioxide reduction performance to formate.In the H-type replaceable membrane electrolytic cell with CO₂ saturated 0.5 M KHCO₃solution,the Faraday efficiency of formate products exceeds 90%in a wide potential range of-0.9 to-1.3 V vs.RHE,and reaches the maximum FE value of 93.5%at-1.1V vs.RHE.In the alkaline solution of gas diffusion electrolytic cell,the Faraday efficiency of formate product exceeds 90%in the range of-0.5 to-1.0 V vs.RHE,and reaches the maximum value of 94%at-0.7 V vs.RHE,and has excellent chemical and structural stability.Through electrochemical in-situ Raman characterization technology,it is revealed that the excellent formate production performance of InS NRs catalyst is due to the nanorod structure with large specific surface area and the introduction of S element.The design of nanorod structure promotes the enrichment of CO₂ on the catalyst surface and exists in the form of bidentate adsorption state（*OCO*）.Moreover,the sulfur atom accelerates the dissociation of water to form adsorbed hydrogen（H*）,further promotes the reaction between H*and*OCO*to form*OCHO*intermediate,and further desorbs to form formate（HCOO^-）,which greatly improves the electrocatalytic formate production efficiency of indium sulfide catalyst.Replacing the oxygen evolution reaction（OER）in the anode compartment with a more thermodynamically and kinetically favorable methanol oxidation（MOR）to further assist the CO₂RR in the cathode compartment to obtain formic acid at lower overpotential and energy consumption conditions salt chemicals.2.A novel Te vacancy-rich nanoporous indium telluride(np-In₄Te_3-x)catalyst was successfully developed by electrochemical dealloying and electrochemical cyclic voltammetry.The np-In₄Te_3-x exhibits excellent electrochemical CO₂ reduction performance in 0.5 M KHCO₃ solution saturated with CO₂.The faradaic efficiency of formate over a wide potential range of-1.1 to-1.3 V vs.RHE exceeds 90%and reached the maximum value of 97%at-1.3 V vs.RHE potential.Through the analysis of electrochemical test results,the obtained np-In₄Te_3-x has a large number of ready-made active sites,excellent intrinsic activity,and superior charge and mass transfer ability,which greatly improves the performance of indium telluride catalysts.Electrocatalytic formate production efficiency.In addition,a unique paired electrosynthesis system of CO₂RR coupled with MOR was constructed,which can exhibit excellent electrocatalytic synthesis performance and efficiently generate formate with close to90%selectivity at the cathode and anode.In summary,this paper constructs nanostructured indium based chalcogenide intermetallic compound catalysts with high catalytic activity through appropriate morphology regulation,heteroatom doping and vacancy defect engineering,which effectively solves the problems of high initial potential,low formate product selectivity and poor catalytic stability of indium catalysts in the process of electrocatalytic CO₂reduction.This work also provides insights into the deep understanding of the relationship between the composition,structure,and performance of catalysts.