Photoelectrocatalytic Reduction Of Carbon Dioxide On Tin Oxide Based Catalysts

Environmental problems and energy shortages become global problems and challenges for human society.In recent years,serious environmental problems of global climate change and rising sea levels are caused by the emission of CO2 from the burning of fossil fuels,bringing a series of hazards to humans and living things.Therefore,it has been a research hotspot for development of non-fossil fuel renewable energy systems.To date,several approaches are being investigated for CO2 conversion as well as electrochemical,photocatalytic,photoelectrocatalytic,or direct catalytic conversions.Among them,the photoelectrocatalysis?PEC?process,combining both of their advantages?PC,EC?,thus provide a promising approach to reduce CO₂.On the one hand,the light irradiation reduces external energy input for photo-generated electrons excited in the photocatalytic?PC?process.On the other hand,the applied potential can not only accelerate the separation of photoinduced carriers but also produce electrons in the electrocatalytic?EC?process.The key to the success is the design combination of the catalyst.In this work,SnO₂nanopores were prepared by electrochemical anodization,using Tin plate as substrate,and then SnS₂ and Ce₂S₃ were assembled on SnO₂ nanopores?NPs?,then the assembled catalysts as the research object.Our study found that the prepared SnO2 was nanopore structure.By the electrochemical characterization shown that the electrochemical adsorption capacity of SnO2was 2.14 nmoL,which was 11.26 times larger than that of Sn sheet.The conversion efficiency of SnO₂ NPs reached up to 46.30%,which was twice as high as that of Sn sheet.The electrocatalytic reduction product was methanol.After 7 h electrocatalytic reaction at-0.8 V?vs SCE?,the methanol concentration reached a maximum of 78.89?mol L^-1 cm^-2,which was 6.04 times that of the Sn sheet yield(13.07?mol L^-1 cm^-2).The Faraday current efficiency of the electrocatalytic reduction of SnO₂ NPs reached about 50%,which was 2.5times that of the Sn sheet.However,the wide energy band gap?3.5 eV?of SnO₂ can't use visible light.So the narrow gap of SnS₂ was choosen to modify SnO₂ to expand the the visible light region.The SnS2 NRs/SnO2 NPs composite catalyst was prepared by hydrothermal method.It was found by SEM that SnS2 tended to grow in one-dimensional rod shape.The band gap Eg was 2.22 eV by optical characterization,which broadened the absorption range of light.After the load of SnS₂,EIS value is reduced by 5.38 times compared with the SnO₂NPs impedance value.The product for the reduction of CO₂ was methanol.After 7 h photoelectrocatalytic reaction at-0.7 V?vs SCE?,the methanol concentration reached a maximum yield of 206.23?mol L^-1 cm^-2,which was higher than the yield of electrocatalytic alone(120.33?mol L^-1 cm^-2).The Faraday efficiency of photoelectrocatalysis was about 74%,while the single electrocatalytic Faraday current efficiency is about 54%,which reflectsed the synergistic effect of photocatalysis and electrocatalytic reduction.The photocatalytic properties of SnO₂ modified by SnS₂ were improved,but the conduction band position of the obtained composite electrode was-0.40 eV,and the reduction potential of CO2/CH3OH was-0.38 eV,the conduction band position was not negative enough,leading to the weak reduction ability and poor photocatalysis performance.Therefore,Ce₂S₃ with a more negative conduction band position were selected to match the SnO₂ assembly,which further improved the photocatalytic reduction ability.The composite catalyst of Ce2S3 NSs/SnO2 NPs was prepared by hydrothermal method.Ce₂S₃ tended to grow in a sheet form by SEM.The band gap?Eg?was 2.0 eV by optical characterization.After loading Ce₂S₃,the EIS of Ce₂S₃NSs/SnO₂ NPs is smaller 11.09 times than that of SnO₂ NPs.The conduction band position obtained was-0.77 eV from the Mott-Schottky curve.The main product of the reduction of CO₂ was methanol.The maximum yield of methanol was 557.25?mol L^-1 cm^-2 after 7 h for photoelectrocatalytic CO2,which was 2.70 times than that of SnS2 NRs/SnO2 NPs and 7.06times that of SnO₂ NPs.It indicated that the more negative the conduction band position of the electrode is,the more favorable the photocatalytic reaction is,and the better the photoelectric synergistic catalysis is.The nanoporous catalyst has strong adsorption capacity for CO₂,which can increase the initial concentration of CO2,and provides favorable conditions for the next step of catalysis.This provides a design concept for improving the catalytic reduction performance from the material morphology.The catalyst with high negative conduction band was prepared by band-matching theory,the more negative conduction band is,the better photocatalytic reduction ability is,which provided a theoretical basis for design of materials for photocatalytic reduction of CO₂.