| The excessive emission of carbon dioxide has caused serious environmental problems and threatened the sustainable development of human civilization.Electrochemical carbon dioxide reduction(CO2RR)reaction to produce high-value fuels and chemicals is one of the promising ways to solve this problem.A key challenge hindering the development of CO2RR technology is the slow reaction kinetics,which can be solved by high efficiency electrocatalysts.As the electrocatalyst of CO2RR,precious metals show excellent catalytic activity and good stability.However,due to the limited availability of precious metal catalysts,such as platinum,palladium or gold,and the product is mainly CO,it is difficult to synthesize other high value-added chemicals.It is necessary to replace them with more abundant elements.As one of the rich transition metal elements,copper can catalyze the formation of deep reduction products of CO2RR(including HCOOH,CO,CH3OH,C2H4,C2H5OH,etc.)with acceptable activity and efficiency,which has been widely concerned by researchers.Due to the lack of theoretical guidance,it takes a lot of time and energy to find highly active and selective catalysts.In order to study the CO2RR catalytic system more quickly and deeply,it is necessary to find an efficient analysis and detection technology to achieve high-throughput screening of catalysts.Scanning electrochemical microscope(SECM),as a member of scanning probe technology,has been used to explore the local electrocatalytic activity of material microstructure because of its high spatial resolution and rapid detection of electrochemical active sites.In this paper,we use scanning electrochemical microscope to construct and explore the catalytic behavior of copperbased materials in the process of carbon dioxide reduction,and systematically study the activity and selectivity of copper-based catalysts at different potentials.The main contents of this thesis are as follows:1.Based on scanning electrochemical cell microscope(SECCM)technology,copper-doped sodium chloride solid solution microcrystals were synthesized in situ and assembled into microdevices.In the process of synthesizing copper-doped sodium chloride solid solution,the redox behavior of Cu(Ⅱ)-Cl system in the microelectrochemical cell was studied.The CV curve showed that the microdroplet contact between the microtubule and the substrate was supersaturated,which conformed to the thin layer electrochemical response characteristics.Then,by constructing the microcrystal between 2.5 μm spaced gold electrode pairs,the "solid" redox behavior of a single copper-doped sodium chloride microcrystal in the absence of electrolyte was studied.It is found that there is a well-resolved transformation between zero valence,univalent and bivalent Cu in the microcrystal.It should be noted that the adsorbed water provides H+ as a pair of ions plays an important role in the whole system.With the continuous progress of potential scanning,the solid-state CV curves of microcrystals gradually show semiconductor characteristics.2.The electroreduction of CO2 catalyzed by truncated octahedral cuprous oxide microcrystals was studied by scanning electrochemical microscope.The cuprous oxide catalyst was dripped and dispersed on the glassy carbon electrode as the working electrode,and the SECM catalytic CO2RR was studied by using the feedback mode of Cu2O NCs.By applying different potentials(-0.3 V to 1.6 V vs.Ag/AgCl)to the glassy carbon electrode substrate loaded with Cu2O catalyst,it is found that the hydrogen evolution reaction occurs preferentially at the lower overpotential(-0.9V vs.Ag/AgCl).The oxidation peak of formic acid was not observed on the CV curve of platinum microelectrode until the substrate potential was up to-1.1 V vs.Ag/AgCl.And the broad peak of CO oxidation was observed at the higher overpotential(-1.5 V vs.Ag/AgCl).Therefore,SECM can be used to accurately study the initial potential of CO2RR and the formation of potentialrelated products.3.A series of CuBi bimetallic microdot arrays were Electrodeposited on glassy carbon electrodes by scanning electrochemical cell microscopy.The morphology and catalytic performance of the catalyst nanostructure were adjusted by adjusting the electrodeposition parameters,that is,the electrodeposition time(100 s,300 s,500 s)and the molar ratio of copper to bismuth in the electrolyte(1:1,3:1,5:1).Then,the carbon dioxide reduction reaction activity imaging of the deposited microdot array was carried out at the same time by using the feedback mode of scanning electrochemical microscope.Among them,the micro-spot activity of the catalyst with electrodeposition time of 100s and molar ratio of copper to bismuth of 5:1 is the highest Using the SG/TC model,it is found that under the condition of weak polarization(-1.2 V vs.Ag/AgCl),the hydrogen evolution reaction(HER)appears preferentially on the surface of the electrodeposited CuBi bimetallic catalyst nanostructure,and the formate product is formed at a higher overpotential(-1.5 V vs.Ag/AgCl).It is also proved that bicarbonate can not be directly reduced to formic acid without CO2. |
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