Design Of TiO₂-based Electrocatalysts And Its Performance Study In Electrocatalytic Nitrogen Reduction

Ammonia（NH₃）is an important chemical feedstock that is widely used in agriculture,industrial chemical production,and manufacturing.Today,the demand for NH₃ is increasing due to its extremely high hydrogen storage capacity,ease of storage and transportation and high energy density.In industrial production,the Habor-Bosch process,invented in the early 20 th century,is still used for the large-scale synthesis of NH₃,but since the process requires high temperatures and pressures near 300-400°C and 150-300 atm,high-purity H₂ is obtained from fossil fuels and use iron（Fe）/ruthenium（Ru）catalysts,which consumes about 1%-2%of the global energy supply and contributes of 1%global gas emissions.Therefore,there is an urgent need to develop green and sustainable methods for NH₃ production.Electrocatalytic systems are an attractive pathway for NH₃ production.Not only does the reaction take place at ambient temperature and pressure,but the system is driven by electricity and the reaction process can be precisely localized by observing the voltage or current,or experimentally adjusted by varying that.In addition,the source of hydrogen for electrocatalytic nitrogen reduction（NRR）is replaced by the water（H₂O）,which avoids significant energy consumption.Titanium dioxide（Ti O₂）is widely used in electrocatalytic NRR as a highly flexible semiconductor catalyst with abundant reserves,low cost,relatively non-toxic and non-hazardous and high thermal stability.However,its application in electrocatalytic NRR is still very limited due to its own deficiencies low electrical conductivity,stable N≡N in N₂ molecules in electrocatalytic reactions,difficulty in activation hydrogenation,harder detachment of NH₃ and competitive hydrogen evolution reaction（HER）.Therefore,the search for electrocatalytic methods that can promote the activated cracking of N₂ and inhibit the occurrence of HER is an important issue in the field of electrocatalytic NRR.This problem can be solved by surface modification of the electrocatalyst to change the electronic structure of the catalyst surface or improving the electrolyte solution to increase the reaction sites,thus promoting the cleavage and hydrogenation of N₂ molecules and improving the performance of electrocatalytic NRR.This thesis reports a series of modulations in the field of electrocatalytic NRR by design modification of Ti O₂,and the main research is as follows:（1）In this section we successfully synthesized black Ti O_2-x with oxygen vacancies（OVs）(which we named B-Ti O_1.8)for electrocatalytic NRR by inserting H into the Ti O₂ lattice.Compared with the untreated Ti O_1.93,B-Ti O_1.8 exhibited excellent electrocatalytic NRR activity.The experimental results showed that the highest NH₃yield and stability reached 31.6μg h^-1 mg_cat^-1 and 100 h at-0.1 V（vs.RHE）and the highest Faraday efficiency（FE）reached 47.7%at 0 V（vs.RHE）.（2）In this section,we report for the first time in the field of electrocatalytic NRR·H,which is generated using sulfite(SO₃^2-)and H₂O from the electrolyte with UV irradiation.The highest NH₃ yield can achieve 100.7μg h^-1 mg_cat^-1,stability can achieve 64 h and FE can achieve 27.1%in the solution with UV irradiation at-0.3 V（vs.RHE）.The experiments and DFT calculation analysis showed that the presence of SO₃^2-in the solution greatly reduced the reaction energy barrier and increased the reaction activity.