Preparation Of Titanium Dioxide Based Heterojunction Catalyst And Its Research On Electrocatalytic Nitrite Reduction

As one of the most important chemical products in the world,ammonia（NH₃）has high hydrogen mass density,high energy density and low liquefaction point,so it is regarded as a promising carbon free energy carrier.Haber-Bosch method is mainly used for large-scale production of NH₃ in industry.However,this method can consume a lot of energy and cause a lot of carbon dioxide emissions,which will cause serious pollution to the ecological environment.Nitrite（NO₂^-）is a kind of pollutant widely existing in urban groundwater,which is easy to cause public health problems.Electrocatalytic reduction of nitrite to ammonia is a green method under normal temperature and pressure.However,the reduction of nitrite to ammonia is a complex six electron transfer process,which urgently needs efficient and highly selective catalysts to promote this process.As a typical transition metal oxide,titanium dioxide（TiO₂）has the advantages of stability,cheapness and safety.However,its low conductivity and weak activation ability limit its application in electrocatalysis.Loading transition metals on the surface of titanium dioxide can improve its conductivity,which is an effective strategy to improve catalytic performance.However,there is relatively little research on its application in electrocatalytic NO₂^-RR.Based on this,this paper first synthesized the metal semiconductor heterojunction catalyst based on TiO₂ nanoribbons through hydrothermal,ion exchange and high-temperature annealing methods,then determined its composition and morphology through physical structure characterization,then tested and analyzed its electrocatalytic NO₂^-RR performance using electrochemical technology,and finally analyzed the reaction path and the source of high catalytic activity through density functional theory（DFT）calculation.The main research results are as follows:We have constructed a unique metal semiconductor Schottky heterostructure and synthesized a titanium dioxide nanoarray loaded with silver elemental particles on a titanium sheet substrate（Ag@TiO₂/TP）.This article tested its NO₂^-RR performance in alkaline electrolytes（0.1 M Na OH+0.1 M NO₂^-）and reached the highest Faraday efficiency（96.4%）at a potential of-0.5 V vs.RHE.At this time,the yield of NH₃ was514.3μmol h^-1 cm^-2 which is superior to most reported catalysts under the same test conditions.Meanwhile,Ag@TiO₂/TP also has catalytic stability for up to 12 hours.Based on the excellent catalytic activity of TP,in order to further explore the influence of electron transfer direction on catalytic activity and reveal the reaction mechanism,this paper synthesized nickel supported titanium dioxide nanoribbons with higher work functions by changing experimental conditions（Ni@TiO₂/TP）and tested the electrocatalytic performance of NO₂^-RR.In the same alkaline electrolyte,the Faraday efficiency reached its highest value（98.5%）at-0.5 V vs.RHE,at which time the yield of NH₃ was 568.7μmol h^-1 cm^-2,better than Ag@TiO₂/TP.Meanwhile,in neutral electrolytes and low concentration electrolytes,Ni@TiO_2/TP also has high activity towards NO₂^-RR.In addition,DFT calculations have revealed that the formation of Schottky heterostructures enhances catalytic activity.The metal loading not only enhances the conductivity of semiconductors and promotes electron transfer,but also provides a very low rate determining step,which is conducive to the reaction.kel loaded titanium dioxide（Ni@TiO₂/TP）for the ammonia production performance of NO₂^-RR.The electrochemical test result shows that in the same alkaline electrolyte,the Faraday efficiency reaches the highest value（98.5%）at-0.5 V vs.RHE,and the yield of NH₃ is568.7μmol h^-1 cm^-2。Meanwhile,in neutral electrolyte,Ni@TiO₂/TP also has high activity for NO₂^-RR.The stability test proved the durability of the catalyst.In addition,DFT calculation demonstrated that Ni@TiO₂ performs as a heterostructure,Ni loading not only improves the conductivity of the material and promotes the transfer of electrons,but also provides a very low potential determining step,which is conducive to the reaction.