Design And Fabrication Of Novel Catalysts For CO And C₂H₄ Production By Electrocatalytic CO₂ Reduction

The excessive use of fossil energy energy causes the increasing carbon dioxide in the atmosphere,and the resulting greenhouse effect will lead to global warming.Electrocatalytic carbon dioxide reduction can effectively fix the carbon dioxide and convert it into high-value chemicals to realize the carbon cycle.There are many products of carbon dioxide reduction,including CO、HCOOH、CH3OH、CH4、C2H4、C2H5OH、CH3COOH、C3H8O,etc.Among them,CO and C2H4 are respectively the main gas for preparing hydrocarbon fuel in the Fischer-Tropsch process and the main raw material for synthesizing polyethylene in the chemical industry,and both have high economic value.Since the hydrogen production reaction occurs relatively easily in the aqueous phase,it greatly reduces the selectivity and activity of carbon dioxide reduction.Therefore,it is of great significance to improve the selectivity and activity of electrocatalytic reduction of carbon dioxide to produce CO and C2H4.By adjusting the size and morphology of precious metals,the selectivity and activity of CO production can be effectively promoted.However,the high cost of precious metals greatly limits their industrial applications.Therefore,it is very urgent to develop low-cost electrocatalysts with high CO selectivity and activity.For the more complex C2 product C2H4,the Cu-based catalyst is currently the only material system that has the potential to achieve mass production of C2 products(C2H4,etc.).It has a very good stabilizing capacity for the reaction intermediate*CO of the C2 product,which in turn promotes C-C coupling and exhibits excellent C2 performance.By adjusting the size,morphology,crystal plane and modification of Cu nanoparticles,the selectivity(～30%)and activity can be further improved.In recent years,Cu2O has been found to have better C2 selectivity(～45%)and activity than metallic Cu.Its performance may come from Cu(Ⅰ)has better adsorption capacity for*CO species.At present,the control of Cu2O nanoparticles is mainly modified from the perspective of their morphology,crystal plane and doping.However,the selectivity of electrocatalytic carbon dioxide to produce ethylene is still below 60%.Therefore,how to further enhance the selectivity and activity of ethylene is currently a major challenge.In view of the above-mentioned scientific problems,this paper uses interface engineering to construct an effective interface for electrocatalytic carbon dioxide reduction,enhance the quality activity of precious metals,increase the active site of the reaction,and reduce the thermodynamic energy barrier of the reaction to achieve electrocatalytic carbon dioxide selectivity And activity enhancement.The specific research contents of this paper are as follows:In the first chapter,we first briefly introduced the carbon cycle and carbon dioxide reduction,and then introduced the principles,performance parameters,influencing factors,material systems,and technical-economic analysis of electrocatalytic carbon dioxide reduction.It also summarizes the research status and problems of electrocatalytic carbon dioxide reduction.Lead to the significance and research content of this paper.In Chapter 2,the effect of the AZ/C/Ag composite interface on the selectivity and activity of electrocatalytic reduction of carbon dioxide to CO is studied.The AZ/C/Ag composite electrode was successfully prepared by loading a silver-carbon mixture containing only～0.5wt%silver nanoparticles on anodized Zn sheets.Compared with the AZ electrode and the GCE/C/Ag electrode,the AZ/C/Ag composite electrode has higher Faraday efficiency(86%),current density(7.3 mA cm-2),and mass activity(CO)～410 mA/mg).The experimental results show that the AZ/C interface and Ag/C are active interfaces for electrocatalytic CO2 reduction.The coexistence of the two interfaces further increases the electrocatalytic active site of the AZ/C/Ag electrode and enhances the electrocatalytic performance of the composite electrode.Density functional theory calculations show that the AZ/C/Ag electrode has a stronger adsorption capacity for both CO2 and the reaction intermediate*COOH,so it has a lower reaction thermodynamic energy barrier and better electrocatalytic performance.This work provides a novel and simple method to prepare highly efficient electrocatalytic reduction of CO2 catalyst with high selectivity,activity and stability.In Chapter 3,the effect of Cu2O/C interface and carbon defect regulation on the selectivity and activity of electrocatalytic reduction of carbon dioxide to C2H4 was studied.Three kinds of Cu2O/C composites,Cu2O/G,Cu2O/LDC and Cu2O/HDC,were prepared by in-situ growth of cuprous oxide nanoparticles on carbon with different defect levels.The defect degree of the material was characterized by Raman spectroscopy.The interaction mechanism of Cu2O and C was characterized by infrared and X-ray photoelectron spectroscopy before and after the reaction.The results show that there is a stronger interaction between the high-defect carbon and cuprous oxide,which can form a bond through an oxygen bridge,improve the dispersion of cuprous oxide,and increase the number of Cu2O/C interfaces.The electrocatalytic test results showed that the selectivity of C2H4 for the three samples increased in the following order,namely Cu2O/G<Cu2O/LDC<Cu2O/HDC(FEc2H4 was 5%,20%and 50%,respectively).Cu2O/HDC composites with high-defect carbon as the carrier have higher electrocatalytic selectivity for carbon dioxide to ethylene.This study,combined with defects and interface engineering,provides a new idea for improving the selectivity of electrocatalytic carbon dioxide.In Chapter 4,the influence of the construction and adjustment of the interface between Cu2O {100} and {111} crystal planes on the selectivity and activity of electrocatalytic carbon dioxide reduction to C2H4 was studied.The t-Cu2O nanoparticles exposed to {100} and {111} crystal planes in 0.5M KHCO3 had a C2H4 Faraday efficiency and current density values of 59%and 23.1 mAcm-2 at-1.1 V,respectively.This is better than o-Cu2O nanoparticles with {111} crystal plane(45%,16.4 mA cm-2)and c-Cu2O nanoparticles with {100} crystal plane(38%,10.6 mA cm-2)Catalytic performance.Studies have shown that the activity of electrocatalytic CO2 preparation of C2H4 by Cu2O nanoparticles originates from the oxide itself,rather than the metallic Cu nanoparticles produced on the surface during electrocatalysis.The excellent preparation of t-Cu2O nanoparticles as a C2H4 energy source acts on the interface between {100} and {111} crystal planes,which not only promotes C-C coupling and C2H4 desorption,but also promotes slow reaction kinetics.This work may provide a new way to improve electrocatalytic CO2 reduction selectivity through crystal plane and interface engineering.On this basis,in the absence of surfactants,using the solubility of the copper source in the aqueous solution is different,through the in-situ reduction method,successfully prepared a small size that simultaneously exposed {100}and {111} crystal planes Cuprous oxide nanoparticles st-Cu2O.Compared with the relatively large cuprous oxide nanoparticles bt-Cu2O,st-Cu2O has better electrocatalytic carbon dioxide production ethylene selectivity(69%vs 59%)and activity(30 vs 23 mAcm-2).This study proves that it is feasible to increase the number of active sites on the interface by controlling the size of Cu2O without changing the morphology of Cu2O.This paper provides a new method for preparing Cu2O nanoparticles with small morphology and special morphology under the condition of no surfactant,and provides a new way to improve the electrocatalytic carbon dioxide reduction selectivity.Chapter 5 summarizes the main achievements and innovations of this paper,analyzes the problems in the current work,and looks forward to the next solution plan.In short,electrocatalytic carbon dioxide reduction is one of the important means that can effectively realize the natural carbon cycle,reduce the "greenhouse effect’caused by carbon dioxide,and convert it into chemical products with economic value.In this paper,we focus on the key scientific issues of the lack of efficient and inexpensive electrocatalysts in the field of electrocatalytic carbon dioxide reduction and the low selectivity of multi-carbon products.Based on the relationship between the structure and performance of nanomaterials,we studied the effect of multi-component materials on electrocatalytic performance.We designed composite electrocatalysts,such as AZ/C/Ag,Cu2O/C,Cu2O {100}/{111} catalysts,and proposed some methods to improve the selectivity and activity for electrocatalytic carbon dioxide reduction by interface control through studying the kinetics and thermodynamic process of electrocatalytic carbon dioxide reduction.We provide relevant methods and ideas for the design and preparation of new electrocatalytic materials with high selectivity,high activity and low cost,and it is of great significance for further promoting the development and practical application of electrocatalytic carbon dioxide technology.