Surface Sites Optimization Of BiVO₄ Based Heterostructure And Study On The Performance Of Photoelectrochemical Ammonia Production

Ammonia（NH₃）widely used in fertilizers and industrial production,and is an important inorganic chemical product.At present,the main sources of NH₃ are biological nitrogen fixation based on molecular nitrogen and traditional Haber-Bosch process.However,the biological nitrogen fixation cannot meet the huge humans demand for NH₃,and the Haber-Bosch process requires strict reaction conditions,with high energy consumption and serious pollution issues.In contrast,photoelectrochemistry（PEC）nitrate reduction reaction（NIRR）is an ideal green and efficient NH₃ production technology,which alleviates the environmental pollution and energy crisis.Exploring efficient catalytic materials with low cost and strong adsorption activation ability is an important research direction in the field of PEC NIRR to produce NH₃.Therefore,we have successfully prepared a series of photocatalysts with rich surface active site,fast reaction kinetics,high selectivity and light utilization,and successfully applied in PEC NIRR to produce NH₃.The specific work contents are as follows:（1）We designed the chemical microenvironment on the catalyst surface and understood the association between entropy effects and polymetallic components with the help of amorphous metal oxides（A-M_xO_y）.A-M_xO_y was successfully loaded on on p-type Bi VO₄（p-Bi VO₄）surface by hydrothermal method,further revealing the effect of entropy on NIRR performance in PEC system.The morphology and crystal phase of A-M_xO_y/Bi VO₄ samples were characterized by transmission electron microscopy,X-ray diffraction and other methods.Based on ultraviolet visible-near infrared spectra and ultrafast transient absorption spectrum analysis,the entropy regulated Co Fe Mn O/Bi VO₄ exhibits the best PEC NIRR performance.A-M_xO_y not only broadens the photoresponse ability of p-Bi VO₄,but also enhances the charge transport capacity.Under the low bias voltage of-0.1 V vs.RHE,the NH₃ yield rate of Co Fe Mn O/Bi VO₄ sample reached 17.82μg·h^-1·cm^-2.This study demonstrates that the entropy regulation strategy provides a feasible approach for obtaining efficient photocatalysts.（2）The activity of PEC NIRR can be further improved by improving the active site on the catalyst surface.Ce O₂ rich in oxygen vacancies(V_Os)was modified on the surface of p-Bi VO₄ by hydrothermal method,while the C-layer coating effectively improved the stability and conductivity of Ce O₂/Bi VO₄.We have confirmed the crucial role of the frustrated Lewis pairs（FLPs）structure formed by V_Os on the Ce O₂ surface in order to improving PEC performance.The electron density difference diagram and other experimental results show that FLPs can significantly promote the adsorption and activation of NO₃^-,and the NH₃ yield rate reaches 21.81μg·h^-1·cm^-2.This research provides a new perspective for designing PEC NIRR system based on FLPs structure.（3）We loaded Zn In₂S₄ with zinc vacancy(V_Zn)on the surface of p-Bi VO₄ and obtained a new type of Zn In₂S₄/Bi VO₄ heterostructure.The spatial hindrance generated by V_Zn induced the formation of FLPs.The excellent NO₃^-adsorption capacity and conductivity enable the Zn In₂S₄/Bi VO₄ heterostructure to exhibit efficient NH₃production performance.The electron-density isosurface reveals the structure and energy distribution of FLPs.In addition,the isotope labeling experiments have confirmed the accuracy of the NO₃^-→NH₃ evolution process.The NH₃ yield rate of the optimal sample is as high as 29.95μg·h^-1·cm^-2,with a selectivity of 34.1 times that of nitrite（NO₂^-）.Thus,this work confirms the crucial role of FLPs in enhancing catalytic selectivity and kinetics.