Preparation Of Zinc Oxide-based Nanocomposites And Electrocatalytic Reduction Of Carbon Dioxide

In recent decades,electrochemical reduction of CO2 is one of the research topics that people are focusing on,because it can not only reduce the serious impact of the greenhouse effect,but also produce high value-added reduction products to ease the energy crisis.The problems of high cost,low selectivity and poor stability of electrochemical reduction CO2 catalysts are important factors that hinder the further commercialization of electrochemical reduction of CO2.Therefore,in order to reduce cost,increase selectivity,and enhance stability of the catalyst,we focused on inexpensive Zn-based and Cu-based catalysts to carry out our researches regulating their micro-morphology and composition.We prepared different morphologies of ZnO nanomaterials and different ratios of Cu/Zn dandelion-like(CuO-Cu2O)-ZnO nanocomposites,and evaluated their catalytic performance.This work mainly includes the following two aspects:(1)The microscopic morphology of the catalyst has a great influence on the catalytic performance and the Zn-based catalyst has a unique advantage.In view of the above-mentioned facts,we selected inexpensive ZnO nanomaterials as catalysts for electrochemical reduction of CO2.By changing the morphology of ZnO nanomaterials and optimizing them,we investigated their catalytic performance in N2 or CO2 saturated 0.5 mol/L NaHC03 electrolytes.We drew a conclusion that the dandelion-like ZnO nanomaterial synthesized at 50 ℃ had the best catalytic performance.The electrocatalytic reduction of carbon dioxide produced a reduction peak current density of 9.7 mA/cm2,a Tafel slope of 56.17 mV/dec,and the FE of HCOOH up to 85%.This can be attributed to the large specific surface area of dandelion-like ZnO nanomaterials.In addition,the current density produced by the electrocatalytic reduction of CO2 can remain stable within 40 h,resulting from the unique stability of Zn-based catalysts.(2)Based on the fact that the conductivity of ZnO is not strong,the electrochemical reduction of CO2 has a high initial potential and a low current density.We selected the dandelion-like ZnO nanomaterials synthesized at 50 ℃ as the carrier to prepare(CuO-Cu2O)-ZnO nanocomposites with different Cu oxide loadings,and conducted electrocatalytic reduction of CO2 in 0.5 mol/L NaHCO3 solution.Our results showed that the(CuO-Cu2O)-ZnO nanocomposite with Cu/Zn of 0.32 had the best catalytic performance.The initial potential of the electrochemical reduction of CO2 was-0.47 V,the resulting reduction peak current density was-10.98 mA/cm2,and the FE value of the generated CO can reach 95%.Based on the analysis of Tafel slope and EIS data,we knew that the rate-controlling step of electrocatalytic reduction of CO2 by(CuO-Cu2O)-ZnO nanocomposite was electron transfer,that is,CO2 is reduced by electrons to produce CO2·-intermediate.At the same time,adjusting the ratio of Cu and Zn can effectively enhance the conductivity of the catalyst,which leaded to an increase in the electron transfer rate,thereby increasing the catalytic activity of the(CuO-Cu2O)-ZnO nanocomposite.Based on the influence of the morphology and conductivity of the catalyst on its electrocatalytic properties,we prepared dandelion-like ZnO nanomaterials and dandelion-like(CuO-Cu2O)-ZnO nanocomposite.Because of their special structural features and physicochemical bands,they also have a good application prospects in the field of photocatalytic and photoelectrocatalytic reduction of CO2.