Study On Electronic Structur Control And CO₂ Electroreduction Performance Of CeO₂-based Catalysts

The global carbon emissions have caused serious environmental pollution and climate change issues.The conversion of CO₂ into fuels and chemicals by electrocatalytic method provides a long-term viable solution to alleviate global warming and fossil energy shortages.However,electrochemical reduction of CO₂still has been hindered by poor product selectivity and unclear catalytic mechanism.The electronic and surface structure effects of catalysts affect the selectivity of CO₂ electrochemical reduction,of which significantly affects the adsorption of CO₂,the binding strength between catalysts and intermediates,as well as the difference of intermediates during the electrochemical reaction,which leads to a wide distribution of products for electrochemical CO₂ reduction.CeO₂with strong metal-support interaction and rich oxygen vacancies characteristics,which can change the original structure of the metal,adjust the binding energy of the intermediate and the catalyst,and improve the selectivity.In this study,a series of Cu and Zn metals catalysts,with similar structures but significant differences in electron affinity energy,for the electroreduction of CO₂ are designed by using electrostatic spinning technology,and the effects of metal/rare earth metal oxide catalysts on the product selectivity of the 2-electron transfer pathway for the electrochemical reduction of CO₂are investigated,which provides theoretical support for the structural regulation of high-performance electrocatalysts.A combination of electrospinning and sintering processes is used to address the problem that metal Cu cannot be synthesized in one step with metal oxide CeO₂ and C supports.Cu/CeO₂@carbon nanofibers（Cu/CeO₂@CNFs）catalyst with a three-dimensional network structure is synthesized in one step,which facilitates the exposure of active sites.The synergistic effect between Cu and CeO₂ improves the catalytic performance of catalysts,and the optimized catalyst shows a Faradaic efficiency of 59.20%for CO at 100 m A cm^-2,and the CO/H₂ratio could be adjusted over a wide range by adjusting the proportion of the two metal elements.The performance of Zn-based and Zn/CeO₂ catalysts for electroreduction of CO₂ is investigated.Firstly,the ratio of I_D to I_G in carbon nanofibers is indirectly controlled by changing the treatment temperature of electrospun polymer fibers.With the increase of sintering temperature from 600 to 800℃,the I_D/I_G value decreases from 2.59 to 1.52,and the Faradaic efficiency of Zn@CNFs for HCOOH increases from 14.65%to 38.54%at 100 m A cm^-2.In order to improve the selectivity of products,Zn/CeO₂@carbon nanofibers（Zn/CeO₂@CNFs）catalyst is further synthesized,and the selectivity and activity are enhanced due to the electron-donating effect of Zn which changes the electronic structure around CeO₂,alters the binding strength of the intermediates and reduces the activation energy of the reaction.The selectivity of formic acid can reach 77.55%with 150 m A cm^-2.Particle-like,rod-like,and block-like ZnO catalysts are synthesized by changing the anions in the electrospinning precursor.Compared with carbon-based catalysts,metal oxide catalysts can expose more active sites.Compared to other catalysts,particle-ZnO catalyst exhibits more grain boundaries and oxygen vacancies,which contributes to improving the catalytic performance of the catalyst.The particle-ZnO catalyst exhibits the highest Faraday efficiency of about 83%for CO at the potential of-0.96 V（vs.RHE）with 150 m A cm^-2.On this basis,in order to solve the problem of stable oxidation state of the ZnO catalyst during the reaction process,ZnO/CeO₂ catalysts formed by introducing Ce³⁺ions into the electrostatic spinning precursor can stabilize the oxidation state of ZnO by forming a Zn-O-Ce bond at the interface between ZnO and CeO₂.The Faradaic efficiency of the catalyst for CO can reach 90%at-0.69 V（vs.RHE）with 50 m A cm^-2.In situ Raman spectroscopy shows the oxide state of ZnO in ZnO/CeO₂ catalysts remains relatively stable under alkaline electroreduced CO₂environment.