| Electrocatalytic conversion of CO2 to liquid fuels and value-added chemicals is one of the ideal strategies,considering the atomic economy and artificial carbon circle.Moreover,this process can be driven by renewable energy(solar,wind,tidal power,etc.),thus achieving efficient clean-energy utilization.Electrocatalytic CO2 reduction(ECR)can be carried out under ambient conditions,yielding diverse products.However,it faces some challenges such as high overpotential on electrodes,the poor selectivity of C2 and C2+products,the severely competitive hydrogen evolution reaction and the stability in the practice.The rational design and construction of highly active electrocatalysts with low cost,high selectivity,and robust stability are keys to these issues.Metal catalysts,especially precious metal catalysts,show better electrocatalytic performance,but they are often higher costs and lower reserves,so it is difficult to industrialize.In comparison,carbon-based catalysts possess more prominent advantages,such as low cost,abundant reserves,and excellent conductivity,and have excellent application prospects.In this paper,we mainly focus on the electrochemical reduction performance of the carbon-based composite.(1)Cu-MOF prepared by the hydrothermal method was used as the precursor,and the CuS@Cu-MOF composites with different degrees of sulfidation were prepared by sulfidation reaction with different reaction times.The effect of sulfidation degree of Cu-MOF on the electrocatalytic process was researched.CuS-5@Cu-MOF(Water bath reaction for 5 h)electrode material exhibited excellent electrocatalytic performance,and the selectivity to formate reached 76.5%at-1.0 V vs.RHE.After 8 h long time stability test,it was found that the selectivity of formate was still over 65%.(2)Using CuS-5@Cu-MOF synthesized by work(1)as the precursor,copper sulfide with spherical carbon coating was prepared after coating by dopamine and carbonization treatment.In this process,the influence of carbon content on catalytic performance was mainly explored.The results showed that Cu1.96S@NC-240 electrode material exhibited excellent electrocatalytic performance,and the selectivity to formate reached 75.2%at the operating potential of-0.9 V vs.RHE.After 10 h long time stability test,it was found that the faraday efficiency of formate did not significantly decrease,indicating that carbon layers are beneficial to improve the stability of the material.In addition,the overpotential of CO2 reduction to formate also decreased significantly,which further highlighted the advantages of carbon layers.(3)In this section,carbon fiber paper was used as the substrate,and Cu-MOF was grown in situ.Meanwhile,CuS nanosheets with small sizes were prepared after vulcanization and reduction.The CuS nanosheets were uniformly distributed on the surface of the carbon matrix.The selectivity of Cu1-xS/CF-6 to formate was 65%and the local current density was 7.9 mA cm-2 at the operating potential of-0.9 V vs.RHE.After a long times stability test for 8 h,it was found that the selectivity of formate was still more than 60%,showing relatively excellent stability.At the same time,compared with powder material,the preparation of monolithic electrode is simple,which avoids the influence of the use of organic binder on the catalytic activity and stability.Therefore,the preparation of monolithic electrodes has excellent application potential in the future large-scale application of ECR. |
