| The excessive use of fossil fuels has caused a large amount of carbon dioxide emissions,which has seriously damaged the carbon balance of natural ecosystems.The electrocatalytic CO2 reduction reaction(CO2RR)driven by sustainable power is considered as an ideal way to achieve CO2 emission reduction.However,there are more than ten kinds of electrocatalytic CO2 reduction products,such as CO,C2H4,CH3OH and C2H5OH,etc.,In addition,CO2RR is faced with problems such as low reaction stability,high reaction overpotential and poor selectivity of reaction products.Therefore,the preparation of electrocatalysts with high stability,low overpotential and high selectivity is the focus of CO2RR research.Co-based materials with high electrical conductivity,unique electronic properties and high activity are widely used in the field of catalysis.However,Co-based materials cannot be well applied in the field of electrocatalytic CO2RR due to their high activity for hydrogen evolution(HER)and poor CO2 adsorption.Zeolite imidazolium ester framework structure material(ZIF)is a kind of material with porous and high specific surface area,which has good gas adsorption performance.The photoactivation cascade electrocatalytic system can effectively reduce the overpotential of CO2RR,improve the reaction current,and improve the selectivity of reduction products.Cu-based materials can catalyze the reduction of CO2 to multi-carbon products,and are considered as a promising CO2RR electrocatalyst.But the selectivity is not high because of the variety of products in catalytic reduction.Carbon dots(CDs)can be used as an excellent electron donor or acceptor,which can effectively regulate the electron transfer behavior in the composite system and improve the catalytic performance.In this paper,CO2RR electrocatalyst based on cobalt-based and copper-based materials were designed and synthesized.The catalytic efficiency of CO2RR electrocatalyst was improved by means of photoassisted and CDs incorporation,which provided a new idea for the design of CO2RR electrocatalyst with high activity and high selectivity.The main research work is as follows:(1)A catalyst C3N4-ZIF/Co(1 wt.%ZIF/Co)for photoactivated cascade electrocatalytic system was obtained by recombining C3N4 with ZIF/Co by thermal polymerization,which can selectively reduce CO2 to CO.Under light,the Faraday efficiency of CO can reach 90.3%when the applied potential is-0.67 V(vs.RHE),which is 30%higher than that under dark condition.In addition,the current density was significantly increased under light condition,and the reaction overpotential was reduced by 200 mV compared with that under dark condition.The experimental results show that,in the reaction process,the photoactivation process replaces the electric activation process,thus reducing the energy barrier of CO2 molecular activation,reducing the overpotential of the reaction,and improving the Faraday efficiency of CO.(2)A series of CuO-NCDs electrocatalysts were obtained by adding different mass amino modified carbon dots(NCDs)in the synthesis process of CuO catalyst.Through CO2RR test,the main product of CO2 reduction by catalyst is C2H4.Among them,the catalyst prepared by adding 2 mg NCDs in the synthesis process(CuO-NCDs-2)has the highest Faraday efficiency of C2H4 product.The addition of NCDs can significantly improve the selectivity of C2H4 in carbon products(from 69.4%to 84.5%).The experimental results show that the addition of NCDs has a significant effect on the electrocatalytic CO2RR process of CuO catalyst.NCDs can not only reduce the electron transfer resistance between Cu/CuO particles,but also accelerate the electron transfer rate in the low frequency scale(<8 Hz).Meanwhile,the electron well effect of NCDs can significantly improve the electron concentration at the reaction interface of the catalyst.These effects together promote the coupling of C-C bond in the catalytic reaction and improve the selectivity of the reduction product C2H4. |
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