Studies On The Preparation And Properties Of Photocathode Materials For Photoelectrochemical Carbon Dioxide Reduction

More and more attention has been paid to the environmental problems caused by the excessive emission of carbon dioxide and the excessive consumption of energy.To eliminate excess carbon dioxide turns to be the goal for researchers.Photoelectrochemical technology,combined the advantages of photocatalysis and electrocatalysis,has been applied for CO₂reduction due to the alternative catalysts and energy sources and the simulatable photosynthesis.Solar energy serves as the force to stimulate the semiconductor to produce photo-induced carriers,and the photo-induced electrons and holes are separated under the external bias,thus photoelectrochemical system can reduce the input energy during CO₂ redution reaction.Carbon dioxide will be converted into carbonaceous compounds,which are further processed into fuels to supply energy,and carbon dioxide will be released again.The virtuous circle will reduce excessive emission of carbon dioxide into the atmosphere and will meet the energy demand at the same time.In this thesis,g-C₃N₄/ZnTe,Zn-ZnTe-ZIF-8 and GO/MAPb Br₃ QDs photoelectrodes were prepared for photoelectrochemical CO₂ reduction.To start with ZnTe,the studied photoelectrode ranges from powder material to film electrode,and the solvent system was expanded from aqueous to non-aqueous electrolyte,which led to an enhanced separation and transfer of photogenerated charge and an improved stability of photoelectrode and the selectivity of CO₂ reduction products.The thesis mainly involves the following contents:（1）The type-Ⅱ g-C₃N₄/ZnTe heterojunction hybrid has been designed and prepared for photoelectrochemical CO₂ reduction.The heterojunction existed in g-C₃N₄/ZnTe accelerates photogenerated electron-hole separation and the interfacial charge transfer kinetics of catalyst/electrolyte.The results show that the highest yield of ethanol at the potential-1.1 V vs.Ag/Ag Cl achieved 17.1μmol·cm^-2·h^-1.The DFT calculation verified that the formation pathway of ethanol:ZnTe is the CO-producing site,then g-C₃N₄ featuring of abundant pyridinic N subsequently accomplishes the C-C coupling process via adsorbing CO and proton-coupled electron transfer.Then ethanol is obtained.The results suggest the rationality of designing catalyst and mechanism prediction.The two components in g-C₃N₄/ZnTe hybrid collectively complete CO₂ reduction and C-C coupling to assemble ethanol following a stepwise pathway,which provides a promising route of artificial photosynthesis for CO₂ reduction.（2）Zn-ZnTe-ZIF-8 photoelectrode was designed and prepared to solve the problems that easy to fall off from the substrate and long carrier diffusion path in powder catalyst.A device-like structure was constructed via the band configuration among zinc foil,ZnTe and ZIF-8.The heterojunction formed between ZnTe and ZIF-8 promotes the separation and transfer of photogenerated electrons and holes.Moreover,ZIF-8 can effectively adsorb CO₂ and provide the catalytic active sites for the interface reaction.In addition,organic solvent serves as electrolyte to inhibit hydrogen evolution,to improve selectivity of product,and to increase the stability of photoelectrode.（3）The catalyst system was further expanded in organic solvent,Graphene oxide（GO）wrapped CH₃NH₃Pb Br₃ quantum dots（MAPb Br₃ QDs）was perpared for photoelectrochemical CO₂ reduction due to the outstanding optical properties and the impermeability of organic molecules through GO.The cation-πinteraction between electron-rich GO with coniugatedπstructure and MAPb Br₃ QDs with CH₃NH₃⁺,served as the electron transport channel,will promote the photo-induced electron-hole separation.And the protective agent GO prolongs the stability time of MAPb Br₃ QDs.Compared with pure MAPb Br₃ QDs,the GO/MAPb Br₃ QDs hybrid is more favorable for photoelectrochemical CO₂ reduction.The highest CO yield at-0.6V vs.Ag wire reached 1.05μmol·cm^-2·h^-1,which was about 4 times as much as CO with pure MAPb Br₃ QDs.This work extends perovskite-based hybrid for photoelectrochemical CO₂reduction from inorganic perovskite to organic-inorganic hybrid perovskite in organic solvent.