Study On Electrocatalytic Carbon Dioxide Reduction With Copper Catalyst

A core challenge in achieving the carbon neutrality is to establish clean and sustainable energy storage and conversion systems.Through electrocatalysis,carbon dioxide(CO2)can be reduced to high value-added chemical raw materials and fuels by using clean electricity produced by renewable energy such as solar energy and wind energy,which can not only reduce carbon emissions,but also effectively alleviate the energy crisis.Among the many products,multi-carbon compounds,such as ethylene,ethanol,acetic acid,and n-propanol etc.,are the most attractive because of the higher energy density and market price.To date,copper(Cu)is the only single-metal catalyst that can effectively reduce CO2 to multi-carbon products.However,the Cu-catalyzed CO2 electroreduction reaction is rather complicated with generating numerous products,and severe the competitive hydrogen evolution reaction,which leads to misestimation of catalytic performance,as well as insufficient selectivity and formation rate of multicarbon products.To address the above problems,we first establish the benchmarks for Cu-catalyzed high-rate CO2 reduction in flow-cell system,aiming to more accurately detect and quantify both the gas and liquid products;And we prepare high-performance Cu catalysts based on the electric field effect and grain boundary effect in electrocatalytic CO2 reduction,aiming to improve the selectivity and formation rate of multi-carbon products.Combining with various advanced techniques such as finite element simulation and in-situ spectroscopy,we deeply investigated the structure-activity relationship of the catalysts.Finally,by in-situ spectroscopy,we reveal in-situ formed hydroxyl(*OH)species decreases the formation rate of multi-carbon products via the competing adsorption with key carbon monoxide intermediates(*CO)in Cu-catalyzed CO2 electroreduction,and propose a pulsed electrolysis strategy to avoid this issue.The more detail achievements of this dissertation are summarized as follows:1.Establishment of the benchmark for evaluating high-speed CO2 reduction performance on Cu catalysts.Using Cu gas diffusion electrode(GDE)as a model,we identified several systematic errors that are often ignored in the measurements of CO2 reduction in flow-cell,including overestimation of gas phase products caused by ignoring CO2 consumption,underestimation of gas phase products due to accumulation at the electrode/electrolyte interface,crossover of liquid products through the ion exchange membrane and through the GDE.We carefully investigated the effects of current density,electrolyte,catalyst layer loading,ion exchange membrane type and other experimental conditions on the above misestimations.The results displayed that the overestimation or underestimation of the Faradaic efficiency can reach 30%,and under some extreme conditions(such as strong alkali as catholyte with a low CO2 inlet flowrate)might exceed 50%.We propose a modified measurement protocol by considering these issues,which allows us to more accurately detect and quantify both the gas and liquid products of CO2 electrolysis in flow-cell systems.2.A multi-tip Cu dendrite catalyst capable of efficiently and stably generating multi-carbon products has been developed.Based on the electric field effect in CO2 reduction,we directly prepared Cu dendritic electrocatalysts with multi-tip structures on gas diffusion layer by electrodeposition.Finite element simulations and in-situ Raman spectroscopy show that the strength of interfacial electric field and the concentration of alkali metal cations near the Cu tip can be increased by more than 5 to 10 times due to the tip discharge effect,which can lower the C-C coupling barrier by stabilizing the key intermediates such as*CO,*OCCO(H)etc.,and thus promote the formation rate and selectivity of multi-carbon products.The activity test in flow-cell shows that the Cu dendrites can achieve the industrial-grade current density of 400 mA/cm2 with the multi-carbon products Faradaic efficiency of 65%.In addition,the Cu dendrites displays excellent catalytic stability in the flow-cell due to firm connection into the substrate and robust hydrophobicity.The electrode can run stably for 140 hours and nearly 50 hours at 120 and 300 mA/cm2,respectively.This study proposes a strategy to increase the strength of interfacial electric field and the concentration of alkali metal ions by controlling the morphology of Cu catalysts,thus promoting the formation rate of multi-carbon products,which provides important insights into the design of high-performance Cu-based catalysts.3.A copper-based perovskite oxide-derived Cu catalyst capable of efficiently generating multi-carbon products in neutral electrolytes.We prepared a grain boundary-enriched Cu catalyst derived from an unconventional copper-based perovskite oxide(La2CuO4)via the in-situ reconstruction.Structural characterization reveals that with the assistance of CO2,the La sites in La2CuO4 can be leached from the lattice,thereby inducing the reduction and rearrangement of internal Cu sites and finally forming a highly active Cu catalyst rich in grain boundaries.Electrochemical tests in neutral electrolytes showed that the catalyst can achieve a total current density of 500 mA/cm2 with the excellent multi-carbon products faradaic efficiency of 80.3%,far exceeding than that of simple oxides(CuO)derived Cu catalysts.Structural characterization and in-situ Raman spectroscopy revealed that the La2CuO4-derived Cu surface is rich in structural defects and low-coordinating atoms,which can enhance the adsorption of*CO intermediates and thus promote the C-C coupling kinetics,but also effectively inhibit the formation of by-product H2.This work highlights the great potential of Cu-based perovskite materials for efficient production of valuable multicarbon compounds via CO2 reduction reaction.4.Removal of the detrimental*OH species in-situ generated on Cu surface in CO2 reduction by pulse electrolysis to promote the formation rate of multi-carbon products.We investigated the speciation of Cu catalysts in CO2 reduction by in situ spectroscopy,and reveal the in-situ formation of*OH species on the Cu surface.Electrode surface kinetics and CORR activity tests showed that the*OH species can strongly adsorbe on Cu surface,and tend to reduce the surface coverage of key*COatop intermediate through the competing adsorption mechanism,thereby significantly reducing the CO2 reduction kinetics and the formation rate of multi-carbon products.We therefore propose a pulsed electrolysis strategy to periodically remove the dentrimental*OH species and to improving promote the coverage of*COatop intermediates,thereby promoting the C-C coupling kinetics and formation rate of multi-carbon products.This study provides new mechanistic insights into the surface dynamics of Cu electrodes during CO2RR,and shed some lights on advanced design of electrocatalysts and operating systems to achieve effcient formation of multi-carbon products.