Fabrication Of Cu₂O Based Nanocomposites For Photoelectrocatalytic CO₂ Reduction

In recent years,with the rapid development of the economy and the overconsumption of natural resources,the concentration of CO2 in the air gradually increases,resulting in "greenhouse effect" The resulting environmental problem and energy crisis have become one of the focal issues of common concern for all mankind.Efficient conversion of carbon dioxide into chemical fuel is one of the effective ways to achieve energy saving and CO2 emission reduction.Exploring the development of new technologies for efficient conversion of carbon dioxide has become an important development direction in the field of energy environment catalysis in the world.As a stable gas,the reduction of CO2 usually takes place under special conditions such as high temperature,high pressure or using catalyst.With the development of CO2 conversion technology,many methods have been developed for CO2 reduction.It is very important for CO2 conversion to choose a method with less energy consumption,simpler operation and higher conversion efficiency of CO2.The main methods of CO2 reduction are photoreduction,electroreduction and photoelectricity co-reduction.The semiconductor-based photocatalysis method is the most promising approach owing to its economy,safety and cleanliness,which requires only the inexhaustible solar light as a driving force,and a suitable semiconductor as a photocatalyst to conduct catalytic CO2 reduction reactions.Cuprous oxide(Cu2O)is known to be a good catalyst for CO2 reduction to hydrocarbon under visible light irradiation.But the recombination of electron-hole pairs and the photocorrosion problem limited its photocatalytic activity and stability.The formation of a heterojunction structure can promote the separation of electrons and holes,reduce the reduction of photogenerated electrons to Cu2O,and enhance its activity and stability.Electroreduction method has been widely concerned by researchers due to its easy control,high efficiency and separation of products from oxidized products.The key of this method lies in the selection of electrode materials to achieve high efficiency and high selectivity to electroreduction of CO2.Copper is the only metal that that can convert CO2 to hydrocarbons by electrocatalytic reduction,and Cu derived from cuprous oxide has become a hot electrode material.The photoreduction method combines the advantages of photoreduction and electroreduction,and is superior to the single photocatalytic system and the single electrocatalytic system.In this paper,we choose Cu2O as the research object and modifed it to improve the performance and stability of catalytic reduction of CO2 for the three methods.The work of this thesis mainly includes the following two aspects:1.Study on Cu2O@Cu metal-semiconductor heterostructure for photocatalysis and photoelectrocatalytic reduction of CO2We used a simple wet chemical method to prepare Cu(OH)2 nanowire precursors,which were calcined in N2 atmosphere to obtain Cu2O,and then the surface of Cu2O was partially reduced to Cu nanoparticles to form Cu2O@Cu metal-semiconductor heterojunction structure.The Cu metal on the surface of Cu2O not only would trap the charges from semiconductor but also act as highly active sites for reactions.By changing the reduction time,we can change the amount of Cu on the surface,and through a series of characterization and catalytic reduction CO2 performance test,we get the best sample Cu2O@Cu-2.Compared with Cu2O,the catalytic performance and stability of Cu2O@Cu-2 have been greatly improved.And Cu2O@Cu-2 has a quantum efficiency of 1.53%for CH4 and C2H4 and still retains 91%activity after four photoreduction cycles under visible light.In addition,an external bias was applied to further enhance CO2 reduction activity by promoting the separation of photogenerated electrons and holes.Substantially,the samples exhibited improved stability as well as decent activity for PEC CO2 reduction at a low external bias compared to that for PC CO2 reduction.2.Study on polymer modified Cu nanowires for electrocatalytic reduction of CO2We modified the Cu(OH)2 precursor with polypyrrole and polyaniline,respectively,and then calcined it in N2 atmosphere to obtain N-doped C modified Cu2O with one-dimensional nanoporous structure,and finally derived Cu@N-Doped C electrode.We found that the Cu@N-doped C sample with pyrrole and aniline in the precursor has a one-dimensional porous rod structure,and the porous structure makes the sample have a larger specific surface area,which can provide more reactive sites.Compared with the samples without pyrrole and aniline,the samples showed better electrochemical properties and could change the selectivity of CO2 electroreduction and promote the conversion of C1 products to C2 products.