Synthesis Of TiO_2-x With Rich Oxygen Vacancies For Nitrate Electroreduction To Ammonia

In recent years,the accumulation of nitrate（NO₃^-）in the surface water and underground aquifer has seriously threatened human health.At the same time,ammonia（NH₃）is one of the chemical products related to the livelihood of human beings.Currently,the Haber-Bosch process is widely used to produce ammonia,but it creates some problems,such as high energy consumption and serious pollution.Therefore,electrocatalytic nitrate reduction into recyclable ammonium（NH₄⁺）under benign conditions is significant.However,its selectivity and efficiency were retarded by the complicated eight-electron reduction course and the competitive hydrogen evolution reaction.Recently,oxygen vacancies（OVs）have been widely used to improve the performance of electrocatalysts.However,exploring OVs-rich oxides as the potential electrocatalysts for ammonium synthesis from nitrate electroreduction is rarely reported.Here,we aimed to design and develop a highly selective electrocatalytic catalyst for nitrate reduction of ammonia synthesis,prepared oxygen-rich vacancy titanium dioxide（TiO₂）nanotubes electrocatalyst,characterized its morphology,structure and composition,and it was used to study the catalytic activity of synthesis of NH₄⁺by NO₃^-reduction.The main results are as follows:In this thesis,TiO₂ nanotubes were obtained by anodizing titanium（Ti）sheet,and TiO₂ nanotubes with rich oxygen vacancies(TiO_2-x)were prepared after high temperature treatment with H₂.The results showed that both TiO₂ and TiO_2-x were anatase crystalline nanotubes.Moreover,compared with TiO₂,TiO_2-x has a higher content of OVs on its surface.The synthesized TiO₂ and TiO_2-x nanotubes were used for the performance test of electrochemical reduction nitrate synthesis of NH₄⁺,and the quantitative analysis of NH₄⁺was carried out by ¹H nuclear magnetic resonance（NMR）spectra and colorimetric methods.The results showed that TiO_2-x nanotubes had good Faraday efficiency（85.0%）,selectivity（87.1%）and stability.Moreover,¹⁵N isotope labeling experiments prove that ammonium originates from nitrate reduction.In addition,online differential electrochemical mass spectrometry（DEMS）and density functional theory calculations reveal the function of oxygen vacancy in nitrate electroreduction,that is,the oxygen vacancy not only"anchors"the oxygen in the nitrate to weaken the N-O bond,but also regulates the interaction between the intermediate and the catalyst,thereby optimizing the reaction path and hindering the formation of the by-products.