The Preparation Of Cu Based Catalysts And Their Performance For CO₂ Eletroreduction

Energy sources has always been a hot topic in scientific research.With no doubt that fossil fuels are still the main energy in chemical industry and our daily life even though some renewable and green energy sources,including solar energy and wind energy,are growing up rapidly with the development of our technologies.As everyone knows,the growing depletion of coal and petroleum resources leads to increasing CO2 concentration in the atmosphere,which raises serious concerns about our health and environment,such as the greenhouse effect.Electrocatalytic reduction of CO2 to fuel or chemical feedstock is an efficient route for simultaneous conversion of CO2 which can not only reduce the CO2 concentration but gain the available energy sources too.Metallic electrodes used in C02 electroreduction have attracted widespread attention during scientific studies.But Cu is the only catalyst known to electrochemically convert CO2 to hydrocarbons and/or oxygenates which arouse much interests of researchers.However,there are still several essential challenges for Cu electrodes in the electrocatalytic reduction of CO2,which include high overpotential,low Faradic efficiency due to the competitive hydrogen evolution reaction and wide product distribution.An effective strategy is to introduce another non-precious metal which has a rich reserves to design a bimetallic or multi-metallic electrocatalysts which possess unique shapes or morphologies,leading to enhanced electrocatalytic performance.Therefore,it is of great significance to study the electrocatalytic performance of Cu based electrocatalysts for CO2 electroreduction.In this thesis,we synthesized CuOx/SnO2 and CuOx/ZnO with different ratios by chemical method and we explore its performance of electrocatalytic CO2 reduction.The main results are as follows:1)CuOx/SrnO2 with different ratios(CuOx/SnO2=1:1;2:1;3:1;4:1)were prepared by co-precipitation of Cu2+ and Sn2+solution and a basic solution(Na2CO3)as precipitating agent at constant temperature.Then we study the performance of all the CuOx/SrnO2 electrocatalysts by performing the electrocatalytic CO2 reduction at constant potential(E=-0.7;-0.8;-0.9;-1.0V vs.RHE).The results demonstrated the selectivity for CO2 electroreduction of CuOx/SnO2 was easily tuned by varying the molar ratio of Cu and Sn.We found that CuOx/SnO2(CuOx/SnO2=2:1)exhibited a high HCOOH faraday efficiency of 73.3%at 0.8V vs.RHE while SnO2 showed a relative low selectivity for HCOOH(FEHCOOH=36.7%).That is to say the CuOx/SnO2 with an optimal molar ratio showed improved higher activity and selectivity for HCOOH.Meanwhile,the selectivity for HCOOH was dropping with higher Cu ratio while the selectivity for CO(FEco=57.8%)became much higher especially for the CuOx/SnO2(CuOx/SnO2=4:1)at-0.9V vs.RHE.So the selectivity between HCOOH and CO can be efficiently tuned by changing the molar ratio of Cu and Sn.2)CuOx/ZnO with different ratios(CuOx/ZnO=1:1;2:1;7:3;4:1)were prepared by co-precipitation of Cu2+ and Sr2+ nitrate solution and a basic solution(Na2VO3)as precipitating agent at constant temperature.Then we study the performance of all the CuOx/ZnO electrocatalysts by performing the electrocatalytic CO2 reduction at constant potential(E=-0.7;-0.8;-0.9;-1.0V vs.RHE).The results showed that ZnO exhibited the higher selectivity for CO at all the studied potentials than CuOx/ZnO electrocatalysts while the competitive hydrogen evolution reaction showed much higher activity.And there were no any liquid products for all the catalysts except trace HCOOH was gained at some electrolytic potentials.Therefore,the catalysts prepared by this way may not be the suitable catalysts for CO?electroreduction,or the addition of Cu may broke the unique surface strcture of ZnO which led to a low activity for CO2 electroreduction.