Material Design Of Photocatalysts And Electrocatalysts In Photocatalytic Water Splitting And Electrocatalytic CO₂ Reduction

With rapid global economic development and excessive consumption of fossil fuels,issues such as energy crisis and global warming are becoming more and more urgent.In order to solve these problems,new,clean,low-carbon and sustainable energy conversion systems need to be explored.Among them,photocatalytic hydrogen decomposition and electrocatalytic CO₂reduction technologies have attracted widespread attention due to their green and environmental advantages.However,photocatalytic hydrolysis and electrocatalytic CO₂ reduction technologies are still facing problems such as narrow light absorption range,high carrier complexation rate and low product selectivity,which limit their further application.In order to overcome the above problems,this paper modulates and optimizes the microstructure of traditional wide-bandgap semiconductor materials and copper-based materials to enhance their photocatalytic and electrocatalytic performance,and tries to design and develop new high-efficiency,highly selective,low-cost,and stable photocatalysts.The main research contents and conclusions of the paper are as follows:（1）The energy band structure,density of states,band edge positions and photogenerated carrier mobilities of single-walledγ-Ge Se nanotubes were calculated using density functional theory.The results show that the band gap value increases from 0.31 e V to 2.65 e V after transforming the bulkγ-Ge Se structure into nanotubes,and the calculated electron and hole mobilities ofγ-Ge Se nanotubes differ by one order of magnitude,which greatly enhances the separation of electrons and holes in photocatalytic reactions.In addition,it was found that nanotubes with larger radius are more likely to meet the requirement of redox potential for hydrolysis.The enhanced photocatalytic performance of single-walledγ-Ge Se nanotubes was revealed from the theoretical level.（2）Nanotube structures are constructed by curling a single layer of Janus Ga₂SSe material.The relevant properties of Janus Ga₂SSe nanotubes were calculated by HSE06 hybrid density functional method.Compared to monolayers,Janus Ga₂SSe nanotubes have a wider visible light absorption range.In addition,the hole mobility of Janus Ga₂SSe nanotubes is as high as2.89×10⁴ cm²V^-1s^-1,which is conducive to the separation of photogenerated carriers to a certain extent.The nanotube band gap can be efficiently adjusted by applying strain.It is hoped that our research will provide meaningful progress in the development of novel and efficient photocatalysts.（3）The geometric and electronic structures of double-walled（DWGSNTs）as well as triple-walledγ-Ge Se nanotubes（TWGSNT）were studied using heterogeneous density functionals and the effect of wall spacing on photocatalytic performance was investigated.The calculated results show that TWGSNTs exhibit more negative strain and formation energies than DWGSNTs,but the small band gap values of TWGSNT nanotubes are not sufficient for their further applications in water decomposition.Furthermore,the band gap of DWGSNTs can be flexibly tuned by varying the interwall distance and shows the nature of indirect-direct band gap transition at the interlayer distance of 6.61?.The predicted DWGSNTs have a good photogenerated charge separation rate.All these data suggest that double-walled nanotubes are more favorable for applications in photocatalytic hydrolysis.（4）The structural and optical properties of BSe nanotubes were investigated based on density functionals theory.The results show that single-walled BSe nanotubes not only have a stable structure,but also are able to extend the UV absorption range of the monolayer to the visible range.Notably,the single-walled BSe nanotubes have excellent photoreduction ability and high hole carrier mobility(～10³cm²V^-1s^-1).Under uniaxial strain,single-walled BSe nanotubes exhibit a direct-indirect bandgap transition.In addition,the electronic structure of double-walled BSe nanotubes facilitates charge separation and has a broader optical absorption range.Unfortunately,their lower energy band edge positions prevent the overall photocatalytic hydrolysis ability.Our results suggest the potential application of single-walled BSe nanotubes for visible-light-driven photocatalytic decomposition of water.（5）The Cu₂O nanoparticles with different crystalline facets,including p-Cu₂O nanoparticles exposing（110）facets,t-Cu₂O nanoparticles exposing（100）and（111）facets and m-Cu₂O presenting（100）,（111）and（110）facets simultaneously were prepared experimentally and their performance in the electrocatalytic reduction of CO₂ to C₂H₄ was evaluated.The results show that the efficiency of C₂H₄ is highly dependent on the number of exposed crystallographic facets of Cu₂O and that m-Cu₂O exhibits the highest ethylene selectivity（61.61%）.This work provides a new way to improve the selectivity of electrocatalytic CO₂reduction using crystal plane engineering technology.