Studies On The Electrocatalytic And Photocatalytic Properties Of Hollow Structured Titanium Dioxied Based Nanomaterials

The energy crisis and environmental pollution caused by the rapid development of industry is a serious violation of the requirements of sustainable development.The development of electrochemical energy storage devices and hydrogen energy as well as the reduction of carbon dioxide（CO₂）levels in the environment are effective measures to alleviate the energy crisis and environmental pollution problems.Currently,electrocatalysts and photocatalysts have achieved considerable progress in electrochemical energy storage devices,the production of hydrogen energy and the CO₂ reduction in the atmosphere.During electrocatalytic and photocatalytic reactions,electrons or holes migrate to active sites on the catalyst surface to perform redox reactions with the target substances.Electrochemical energy storage devices with high theoretical specific energy density(1350 Wh kg^-1)of zinc-air batteries are of great interest.However,the slow oxygen reduction reaction（ORR）and oxygen precipitation reaction（OER）reaction kinetics during discharge/charge process of zinc-air batteries and other factors lead to high charging and low discharging voltages in zinc-air batteries,and resulting in a waste of energy.In photocatalytic hydrogen（H₂）evolution and CO₂ reduction,the low migration and separation rates of photogenerated electrons and holes make photocatalytic H₂ evolution and CO₂ reduction inefficient.To achieve high charging and discharging voltages of zinc-air batteries,efficient photocatalytic H₂and photocatalytic CO₂ reduction,hollow structured titanium dioxide based nanomaterials have been synthesised and applied to three applications:photo-introduced zinc-air batteries,photocatalytic H₂ evolution and photocatalytic CO₂ reduction.The main research contents and results of this study are as follows:（1）S-scheme titanium dioxide-indium selenide（TiO₂-In₂Se₃）and dual S-scheme titanium dioxide@indium selenide@silver phosphate（TiO₂@In₂Se₃@Ag₃PO₄）heterojunctions with hollow structures were synthesized by the hard template method.The material with hollow structure possesses a large specific surface area,which provides more active sites for electrocatalytic and photocatalytic reactions,and the micro-pores in its shell also increase the diffusion and transport of reactants as well as the absorption of photo energy.The three monolithic materials employed in this work are all semiconductor,and semiconductor-based photocatalysts have great potential for harnessing solar energy to solve energy and environmental problems.（2）In order to solve the problems of high charging and low discharging voltages caused by the slow reaction kinetics of the ORR and OER on the air cathode,we employ the S-scheme TiO₂-In₂Se₃ heterojunction as the air cathode and introduce photo energy into the zinc-air batteries.When the S-scheme TiO₂-In₂Se₃ heterojunction is exposed to light,photogenerated electrons at the CB of TiO₂ migrate to the VB of In₂Se₃.The photogenerated electrons at the CB of In₂Se₃ have the high reduction ability to promote ORR and increase the output voltage during discharge process.At the same time,the photogenerated holes at the VB of TiO₂ have the strong oxidation capacity to promote OER and reduce the input voltage during charge process.As a result,the onset potential in ORR reaches 1.28 V and the onset potential decreases to 0.48 V in OER under illumination,and the zinc-air batteries achieves a high discharge potential of 1.79 V and low charge potential of 0.67 V.（3）To overcome the rapid recombination of photogenerated carriers in the photocatalytic H₂evolution,we apply S-scheme TiO₂-In₂Se₃ heterojunction as photocatalysts.The segregation and migration of photogenerated carriers generated by TiO₂-In₂Se₃ under illumination are similar to those in（2）above.In present work,the biomass furfuryl alcohol（FFAH）serves as a sacrificial agent for h⁺and is oxidized to furfural of practical value.The H₂ yield of TiO₂-In₂Se₃(1.35 mmol g^-1)is11.2 and 5.9 times higher than that of pristine TiO₂(0.12 mmol g^-1)and In₂Se₃(0.23 mmol g^-1),respectively.（4）For the problems of rapid recombination of photogenerated carriers,low CO₂ capture capacity and poor stability of photocatalyst in the photocatalytic CO₂ reduction,we employ a dual S-scheme TiO₂@In₂Se₃@Ag₃PO₄ heterojunction as photocatalyst.The reaction mechanism of TiO₂@In₂Se₃@Ag₃PO₄ under illumination is similar to（3）above.We also investigate the evolution of CO₂ on the photocatalyst surface during the photocatalytic reaction by in situ DRIFTS.The products of photocatalytic CO₂ reduction are CH₄,CH₃OH and CO with yields of 3.98,4.32 and8.2μmol g^-1 h^-1,respectively,and the photocatalysts exhibit excellent cycle performance.（5）We investigate the performance of TiO₂@In₂Se₃@Ag₃PO₄ based photo-introduced zinc-air batteries.Under illumination,the discharging and charging voltages of the ZABs are 1.82 and 0.64V,respectively.