Preparation Of Solar Fuels Based On Cu-Based Catalysts (Photo) Electrocatalysis

Over the past century and a half,the concentration of carbon dioxide in the atmosphere has increased from 280 ppm to 410 ppm due to the massive consumption of fossil fuels.In addition,with the increasing energy demand,the global energy consumption per hour is expected to reach 1.1*10²¹J by 2050,of which more than80%comes from natural fossil resources.The ensuing crisis is the huge amount of carbon dioxide released by fossil consumption,which can lead to global warming and environmental instability.Converting carbon dioxide into useful fuels has always been a dream of the scientific community,as it is a"two birds with one stone"option that can solve both the energy crisis and the environmental crisis.Since carbon dioxide is a stable molecule(?G^o=400 k J mol^-1)with two linearly configured double bonds between the carbon and oxygen atoms,it cannot be converted into value-added chemicals.In the current study,there are three main approaches to address this grand challenge,namely photocatalytic CO₂reduction(i.e.,artificial photosynthesis),electrocatalytic CO₂reduction,and photoelectrocatalytic CO₂reduction.Compared with photocatalytic CO₂reduction,electrocatalytic CO₂reduction has several advantages:(i)the process can be controlled by adjusting the potential and reaction temperature;(ii)since the electrolyte can be recycled,the chemical consumption can be reduced to minimum;(iii)the electrochemical reaction device is compact,modular and easy to scale up.However,in the current state of research,achieving energy-efficient and selective production is challenging due to slow kinetics,even when high electron potentials are applied.Photoelectrocatalysis is considered to be a combination of photocatalysis and electrocatalysis.On the one hand,the potential applied in the photocatalytic process favors the separation of photo-induced charge carriers;on the other hand,the additional light irradiation reduces the overpotential in the electronic process.Photocathodes composed of semiconductors are used not only as catalysts but also for light harvesting.Often,cocatalysts,especially metal complex catalysts,are combined with semiconductors to form hybrid systems to improve selectivity and efficiency.In response to the existing problems in the field of(photo)electrocatalytic carbon dioxide reduction,we have constructed an efficient and stable integrated(photo)cathode through a bimetallic heterojunction approach to improve the activity and selectivity of carbon dioxide reduction to carbon products(CO).The main content and innovations of this paper are divided into the following three parts:(1)Sn O_x-enhanced Cu₂O nanowires(NWs)integrated photocathodes were fabricated by a facile electrochemical(EC)deposition method.The Sn O_x-modified Cu₂O NWs greatly enhanced the activity and selectivity of CO₂/CO.At-0.55 V vs.RHE potential,the CO yield of Cu₂O/Sn O_x/50 integrated photocathode(141.79?mol/cm²/h)is 16.78 times higher than that of Cu₂O NWs photocathode(8.45?mol/cm²/h).The Cu₂O/Sn O_x/50 hybrid NWs photocathode can realize the controllable photocatalytic CO₂reduction of CO₂and H₂O to syngas.The overall Faradaic efficiency of syngas is 90.32%at-0.35 V vs.RHE potential.In addition,the syngas CO/H₂ratio can be adjusted from 2.2:1 to 4.6:1.At the same time,the Cu₂O/Sn O_x/50 hybrid NWs integrated photocathode exhibits excellent stability,the current remains stable during the photocatalytic CO₂reduction process for 12 h,and the FE_COand FE_H2are stable.(2)On the basis of the first part of the work,we continued to modify the Cu₂O photocathode to construct an efficient and stable integrated photocathode.Cu₂O/C10/Ag100 integrated photocathode was fabricated by impregnation,calcination and further pulsed deposition,and a novel photocatalytic CO₂reduction system was constructed for syngas generation.The modified Cu₂O NWs photocathode can efficiently produce syngas(CO/H₂)in ratios ranging from 2.91:1 to 4.46:1 and maintain stability for 12 hours.Furthermore,the maximum Faradaic efficiency of syngas reaches 95.90%at-0.35 V vs.RHE potential.The LSV and EIS analyses confirmed that the charge transfer of the Cu₂O NWs photocathode was greatly enhanced by the modification of the Cu₂O NWs with carbon layer wrapping and further Ag deposition,thereby effectively enhancing the CO₂-to-CO conversion.(3)On the basis of the previous two parts,a novel Cu NWs electrode was further prepared by electrochemical reduction method.This electrode showed excellent hydrogen evolution performance in the electrocatalytic CO₂reduction process,but had no catalytic activity for CO₂reduction.However,the modification of the Cu NWs electrode with a tin-based catalyst greatly enhanced the CO₂-to-CO conversion process.At-0.55 V vs.RHE potential,the Faradaic efficiency of CO can reach85.34%.We can confirm through the activity test comparison that the tin-based catalyst acts as the active site in electrochemical CO₂reduction,which enhances the CO₂-to-CO conversion process.At the same time,through electrochemical impedance test and LSV test,it was found that the modification of tin-based catalyst reduced the resistance of electron transfer to the interface on the Cu NWs electrode,and greatly improved the electrocatalytic CO₂reduction performance.Furthermore,the as-prepared Cu/Sn O_x/8 hybrid NWs electrode exhibited excellent stability during the electrocatalytic CO₂reduction process.