Preparation Of CuInS₂-CuFeO₂ Composites And The Research Of Its Photoelectrical Reduction Properties

The process of industrial production consumes a large amount of fossil fuels and releases a large amount of CO2 into the atmosphere.Excessive CO2 will cause serious greenhouse effect,so the problem of CO2 emission reduction is imminent.CO2 can be reduced to useful chemical products such as methanol,formic acid,and low carbon hydrocarbons through catalytic reduction.This will not only save the use of fossil fuels,but also reduce CO2 emissions.However,due to the limitation of low conversion rate and poor selectivity for photocatalysis and electrocatalysis,using visible light as light source,photoelectrocatalytic reduction of CO2 into organic fuels is of great significance in this research.As a semiconductor photocatalyst,CuInS2 has the problems of high electron-hole recombination rate and narrower corresponding range of light.Therefore,another newly emerging p-type semiconductor,CuFeO2,is deposited on the CuInS2 surface.In view of the good optical properties of CuFeO2,the combination with CuInS2 can effectively enhance the electron transport and provide the possibility to solve the above problems.The CuInS2 film is used as a substrate and the surface is acid-treated.In the dimethyl sulfoxide system,CuInS2-CuFeO2 composites were prepared by annealing by differential pulse voltammetry using copper nitrate and ferric nitrate as raw materials.As the deposition potential rises,the methanol production is realized to increase first and then decrease.When the calcination temperature reaches 400 ?,the methanol yield reaches a maximum value.In this study,a series of investigations were conducted on the preparation process of composite films to find the optimal conditions for preparing composite films.And conduct a photoelectric reduction experiment to find the best reduction conditions.The deposition potential is-1.0?-1.2 V,deposition time is 20 s,annealing at 400 ? for 30min.Reduction was performed at pH=5.2 and the reduction potential was-0.7 V(vs.SCE).Under the optimal conditions,the film was used as a working electrode to participate in the photoreduction experiment,the reduction time was 90 minutes,and the reduction area was 1.7 cm2.The CuInS2 film alone has a methanol product concentration of 0.06 mmol/L.The methanol concentration of the composite film reaches a concentration of 0.19 mmol/L.Methanol production is nearly three times than that of CuInS2 alone.This study was characterized by XRD,Raman and XPS tests to determine the film composition.Through the AC impedance test,the main resistance of the catalytic process was the diffusion resistance of the solution.Cyclic voltammetric scans were performed on the films to study the adsorption H and adsorbed CO properties of both types of electrodes.It was found that CO is an intermediate product of a catalytic reduction process.The experiments of adsorbing hydrogen and adsorbed CO showed that the content of adsorbed CO in the composite film was significantly higher than that of CuInS2,which resulted in a significant increase in methanol concentration.