Preparation Of Transition Metal Doped TiO₂ Nanowires And Their Electrocatalytic Nitrogen Reduction Synthesis Of Ammonia

With the continuous growth of global energy demand and the gradual depletion of fossil fuel resources,the development of an economical,efficient,and environmentally friendly technology for nitrogen reduction to synthesize ammonia has become one of today’s hotspots in the field of chemistry.This study primarily focuses on the electrochemical nitrogen reduction reaction（NRR）for ammonia synthesis under ambient temperature and pressure.Inexpensive and efficient transition metal oxide-based catalysts were investigated,with a series of nanowire structures constructed through electrospinning techniques and post-treatment processes.The electrochemical NRR performance of these materials was examined.In the realm of electrochemical ammonia synthesis,factors such as catalyst design and fabrication,electrode material selection,and electrolyte composition play crucial roles in influencing reaction efficiency and selectivity.Therefore,investigating the reaction mechanism and optimizing reaction conditions are vital for the further advancement of electrochemical ammonia synthesis technology.In this work,experimental observations and a series of characterization results were combined to discuss the effects of transition metal atom doping,crystal phase,and one-dimensional morphology on NRR activity.The structure-activity relationship between the catalyst structure and NRR activity was explored,and the NRR reaction mechanism for transition metal-based catalysts was further understood.Through experimental and theoretical investigations,deeper insights into the mechanisms and characteristics of electrochemical nitrogen reduction for ammonia synthesis were gained,providing strong support for the further development of this technology.This promotes the application of green and environmentally friendly ammonia synthesis technology in fields such as agriculture,pharmaceuticals,and the plastics industry.The specific research work is as follows:1.Using Density Functional Theory（DFT）calculations,we investigated the structural and electronic properties of W-doped TiO₂ as an electrocatalyst in the Nitrogen Reduction Reaction（NRR）.The results revealed that,compared to TiO₂,the Projected Density of States（PDOS）of W-TiO₂ exhibited a significant downward shift in both the valence and conduction bands,leading to the transfer of electrons from the O 2p orbitals to the W 5d orbitals.Changes in the Bader charge density manifested as a decrease in Ti and W atoms and an increase in O atoms,indicating that doping W into TiO₂ leads to a rearrangement of the electronic structure.Furthermore,we observed clear electronic occupancy states near the Fermi level,suggesting that W doping creates more conductive states for electron transfer,which is beneficial for electrocatalytic reactions.At a potential of-0.3 V vs.RHE,a remarkable Faradaic efficiency（FE）of up to 21.45%and NH₃ yield of 16.76μg h^-1 mg_cat.^-1were achieved,significantly surpassing the performance of pristine TiO₂.In addition,W-TiO₂ demonstrated good stability for NH₃ generation,indicating its practical application value.The results indicate that W-doped TiO₂ nanofiber catalysts synthesized via electrospinning with W as an effective dopant can optimize the position of the d-band center,enhance conductivity,impart metallic characteristics to the material,and improve the NRR performance of the catalyst at room temperature through doping-induced defects.2.In this study,vanadium-doped TiO₂（V-TiO₂）was employed as an electrocatalyst for the nitrogen reduction reaction（NRR）,with a focus on the influence of its structural and electronic properties on catalytic performance.The introduction of vanadium alters the local electronic structure of TiO₂,enhancing its conductivity and facilitating electrocatalytic reactions.Experimental results reveal that V-TiO₂ exhibits outstanding NRR activity,achieving high ammonia production rates and Faradaic efficiencies at low overpotentials,as well as excellent stability.The superior performance is attributed to three factors:the advantages of the one-dimensional nanostructure,the overall improvement in the catalyst’s performance due to vanadium doping,and an electrolyte optimization strategy that involves the addition of glycerol to 0.05 M H₂SO₄.This strategy enables high ammonia production rates and Faradaic efficiencies at low overpotentials.At a potential of-0.1 V vs.RHE,a Faradaic efficiency（FE）of 18.87%and a maximum ammonia production rate of 20.87μg h^-1 mg_cat.^-1were achieved,surpassing the previously reported rates for V-doped TiO₂ in lithium sulfate electrolytes.3.In this study,Mo-doped TiO₂ nanowires were employed as electrocatalysts for the nitrogen reduction reaction（NRR）to investigate the influence of their structural and electronic properties on the catalytic performance.X-ray diffraction（XRD）and Raman spectroscopy analyses confirmed the presence of mixed anatase and rutile phases in Mo-TiO₂,which contributed to enhanced charge transfer efficiency.Electrochemical impedance spectroscopy（EIS）analysis revealed that Mo-TiO₂ possessed a lower charge transfer resistance,facilitating an increased charge transfer rate.Annular dark-field scanning transmission electron microscopy（AC-HAADF-STEM）demonstrated that Mo atoms replaced Ti atoms in the TiO₂ lattice,achieving atomic-level doping,which helped modify the band structure of TiO₂ and improve charge transfer efficiency.At a potential of-0.4 V vs.RHE,a Faradaic efficiency（FE）of 16.8%and a maximum NH₃ yield of22.2μg h^-1 mg_cat.^-1were achieved,outperforming pristine TiO₂.Mo-TiO₂ exhibited remarkable performance in electrocatalytic NRR,and its unique structural characteristics along with Mo transition metal atom doping promoted N₂ adsorption and activation,thereby enhancing the reaction rate and selectivity of NRR.