Study On High Efficiency Photoanode In Artificial Photosynthesis Based On Nitride Semiconductor

The resource utilization of CO₂ has gradually become an attentive study in recent years.Among the many strategies for converting CO₂,photoelectrocatalysis reduction of CO₂ has great advantages.Semiconductor catalysts can use solar energy as a renewable energy source,use CO₂ as a raw material,simulate photosynthesis in nature to reduce CO₂ to high-value products such as CO and hydrocarbons,which can not only consume accumulated greenhouse gases to alleviate environmental issues,but also use renewable energy to achieve sustainable development.This thesis focused on the high-efficiency gallium nitride（Ga N）-based semiconductor photoanodes in CO₂ reduction of artificial photosynthesis.In the process of photoelectrocatalysis CO₂,semiconductors have some disadvantages such as the unmatched energy band potential between materials and CO₂ reduction potential,the narrow range of light absorption,the low efficiency of separating photogenerated electrons and holes,and the need for sacrificial materials.In view of the above problems,Ga N was used as the basic material in the research,Al or In elements were doped and electrodes with different structures were prepared to research the effects of various Ga N-based photoelectrodes on CO₂ reduction performance by analyzed the results of electrical properties and reduction performance.Simultaneously,due to the phenomenon that Ga N-based semiconductors can be easily corroded during the reduction process,the NiO co-catalyst spin-coated on the electrode surface was researched to enhance the corrosion resistance of the photoelectrode and improve CO₂ reduction efficiency.The details are as follows:1.This thesis investigated the influence of light absorption range on CO₂ conversion performance.Doping In into Ga N and using In Ga N material as the light absorption layer of the electrode can not only expand the light absorption range of the electrode,but also enhance the ability to convert CO₂ to CO.The influence of the separation efficiency of electrons and holes on the CO₂reduction performance in photoelectrocatalysis reaction was studied.The study found that,although Al Ga N/Ga N electrodes prepared by doping Al into Ga N can improve the separation efficiency of electrons and holes,whereas the wide band gap of Al Ga N materials directly results in lower photoabsorption.To slove this problem,In Ga N was grown on the electrode surface as light absorption layer,the In Ga N/Al Ga N/Ga N electrode can not only increase the electrical performance of CO₂ reduction,but also improve the ability to produce methane（CH₄）in the product.2.The influence of the electron energy at the bottom of the material’s conduction band on the performance of CO₂ reduction was researched.The In_xGa_1-xN/Ga N electrodes with different In contents were used as photoanodes.According to analysis the electrical properties and reduction performance during the reaction,it was concluded that the electrode with In content of 0.9%had the best reduction ability among the same series of photoelectrodes.3.The effect of co-catalyst on the performance of CO₂ reduction was investigated.The NiO materials was spin-coated on the surface of Ga N.The effects of spin coating solution concentration and the number of spin coatings on the CO₂ reduction performance were analyzed.Based on the analysis of morphology,electrical properties and reduction performance,we found that the NiO cocatalyst can improve the ability of CO₂ conversion and protect the surface of electrode from damaged.However,the spin coating solution concentration and spin coating times can adversely affect CO₂ reduction.In conclusion,the electrode prepared under the conditions of the concentration of the spin coating solution with1:400 and spin coating twice exhibited better reduction performance.