Defect Regulation Of Metal Oxides And Their Photoelectrocatalytic Nitrogen Fixtion Performance

The development and utilization of renewable green energy is of great strategic significance for solving the increasingly serious energy crisis and environmental pollution,realizing sustainable development and maintaining the harmony of ecological environment.Ammonia（NH₃）is a potential energy carrier,which is easy to store and transport.The synthesis and development of ammonia is very important for the next generation energy reserve and environmental improvement.Artificial nitrogen fixation（NRR）is a process of converting natural abundant small molecule N₂ into NH₃,which can realize efficient conversion and storage of energy.Photocatalysis and electrocatalysis,as green,environmentally friendly and sustainable processes,are effective synthetic approaches for nitrogen reduction and ammonia synthesis.However,the low electron efficiency of photocatalytic nitrogen fixation and the competitive hydrogen evolution reaction of electrocatalytic nitrogen fixation all affect the yield of nitrogen fixation.Therefore,the first part of this paper regulates the oxygen defect concentration on the surface of the photocatalyst barium Titanate（Ba TiO₃）,and then improves the photoresponse efficiency and carrier mobility under the synergic effect of the external magnetic field and the internal electric field of Ba TiO₃ to strengthen the photocatalytic nitrogen fixation activity.In the second part,Fe dopant was introduced into modified titanium dioxide（TiO₂）to accelerate the electron transfer rate,and Fe doped titanium dioxide（TiO₂）was further bridged on the F surface to adjust the spin state of Fe electron on the surface so that the catalyst could adsorb and dissociate nitrogen more efficiently and improve the performance of electrocatalytic nitrogen fixation.The main research contents are as follows:1.Research on efficient photocatalytic NRR reaction of oxygen deficient barium titanate（Ov-BTO）In this work,we introduce oxygen defect in typical perovskite Ba TiO₃（BTO）to improve visible light absorption and electron transfer rate,and enhance the activity of photocatalytic fixation of N₂ under external magnetic field to achieve efficient coupled solar energy conversion and nitrogen fixation.Firstly,oxygen vacancies are introduced on the surface of BTO by sodium borohydride thermal reduction method.By controlling the reduction time（15 minutes,45 minutes,60 minutes,90 minutes and 120 minutes）,oxygen vacancies with different concentrations are introduced respectively.Meanwhile,spontaneous polarization and internal electric field exist in ferroelectric material BTO.Under the influence of external magnetic field and internal electric field,electromagnetic synergistic effect is produced,which strengthens the activity of photocatalytic nitrogen fixation.Next,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,electron spin resonance spectroscopy（ESR）,X-ray photoelectron spectroscopy（XPS）and X-ray absorption structure spectroscopy（XAS）were used to characterize the structures,and density functional theory（DFT）was used to reveal oxygen vacancy manipulation,Lorentz force induction and oxygen vacancy manipulation Regulation of electron and magnetic properties by spin-selectivity effects.Meanwhile,a series of photocatalytic performance tests have proved that the electromagnetic synergistic effect inhibits the recombination of photoexcited carriers in semiconductor nanomaterials,and promotes the rapid charge separation and adsorption and activation of N₂ under UV-vis irradiation.Under sunlight simulation,the yield of NH₃ can reach 1.90mg/L/h.Therefore,this work provides a promising alternative approach for exploring nitrogen-fixing materials with high photocatalytic performance,and provides ideas for promoting the development of synergistic effects of photocatalysts.2.Fluorine（F）modified iron（Fe）doped titanium dioxide（TiO₂）the research of high-efficiency electrocatalytic NRRIn this work,Fe doped titanium dioxide（Fe:TiO₂）was introduced into the doping level,and then Fe doped TiO₂（F-Fe:TiO₂）was modified by using F surface modification to adjust the surface electronic states of the catalyst,accelerate the electron transfer rate,and improve the electrocatalytic nitrogen fixation activity.Firstly,Fe of Fe Cl₃was doped in TiO₂ by sol-gel method,and the amount of Fe doping was controlled by controlling the molar ratio of Fe Cl₃ to TiO₂（1%,2%,4%,6%,8%and 10%）.Meanwhile,Fe doped TiO₂was soaked with Na F,and F was bridged on the surface of TiO₂.Due to the strong electronegativity of F,Fe（III）is induced to enter a high spin state,and the energy level of the dopant rises,and the Fe 3d orbital electrons are fed back to the N 1πg*orbital,which promotes the adsorption and activation of N₂ molecules,reduces the limit potential of NRR,and improves the performance of electrocatalytic nitrogen fixation.Next,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,electron spin resonance spectroscopy（ESR）,X-ray photoelectron spectroscopy（XPS）,X-ray absorption structure spectroscopy（XAS）and density functional theory calculation（DFT）were used to reveal the introduction of Fe doped TiO₂ doping levels Increasing the charge transfer rate,F surface modification modified Fe electron spin state activated N₂molecule efficient electrocatalytic nitrogen fixation activity.Meanwhile,a series of electrochemical tests proved the NRR performance of F-Modified Fe-doped TiO₂（F-Fe:TiO₂）electrocatalyst at-0.5 V vs RHE.The Faraday efficiency reached 27.67%,and the NH₃ yield reached 27.86μg h^-1 mg^-1_cat..