Preparation And Performance Of Photoelectrode For CO₂ Reduction

The photocatalytic conversion of carbon dioxide to valuable chemicals is not only an effective way to solve the greenhouse effect, but also a clean way to ensure rational use of carbon resources. However, poor efficiency and stability of catalyst limit the blossom of this technic. So the research and development of catalyst with stable performance and high efficiency is needed. TiO₂@g-C₃N₄@Co Pi photoanode and Cu₂O@ZnO photocathode were used to assemble the carbon dioxide catalytic reduction system. The oxidation of water and reduction of carbon dioxide was divided into two reaction chamber. So that carbon dioxide can be efficiently reduced by clean solar energy. This study not only can provide new ideas for clean and efficient conversion of carbon dioxide, but also has important significance for the preparation and application of other photoelectrode in this field. The research results are as follows:?1? TiO₂@g-C₃N₄@Co Pi photoanode was prepared by three processes of hydrothermal method, chemical bath and electrochemical deposition. First of all, the density of titanium dioxide nanorod was adjusted by controlling the concentration of tetrabutyl titanate precursor. Second, the g-C₃N₄ quantity deposited on the surface of TiO₂ was optimized through various concentration of urea in the chemical bath solution. Finally, after 30 min electrochemical deposition, we get the final product TiO₂@g-C₃N₄@Co Pi photoanode composite material. The results indicated that the LSV photocurrent density of TiO₂@g-C₃N₄@Co Pi reaches up to 1.6 m A/cm2, which is 3.8-fold that of TiO₂ nanorod arrays?TiO₂ NRs??0.42 m A/cm2? at bias 1.23 V?vs. RHE?. The photocurrent density of TiO₂@g-C₃N₄@Co Pi was quite stable and more than 90% of the initial photocurrent density was still sustained after continuous 10 h illumination at bias potentials 1.23 V?vs. RHE?.?2? Cu₂O@ZnO composite photocathode was prepared via a facile hydrothermal growth and chemical bath process. Firstly, the spherical Cu₂O particles were grown at Cu substrate with good conductivity by chemical bath. Secondly, ZnO nanobranch was deposited at the surface of Cu₂O particles by hydrothermal growth. This kind of composite structure not only can constitute heterojunction to improve the efficiency of charge separation, but also can greatly accelerate the charge transfer by increasing the surface area. The faradic efficiency of Cu₂O@ZnO as photocathode can reach up to the maximum value 7.9%, at the bias of-1.1 V?vs. SCE?.?3? Under the inspiration of proton exchange membrane fuel cell, we designed a novel phtotoelectrochemical cell with two compartments connected by salt bridge for carbon dioxide reduction. This system was consisted of the prepared n-type semiconductor photoanode TiO₂@g-C₃N₄@Co Pi and p-type semiconductor photocathode Cu₂O/ZnO. Employing the novel system, the reaction of carbon dioxide reduction and water oxidation occurred at the same time in the cathode part and anode part, respectively. Under the bias of-1.0 V?vs. SCE?, the faradic efficiency of CO2 reduction system could get maximum 9.6%.