Synthesis Of Two-dimensional Inorganic Nanomaterials And Their Electrocatalytic Applications

Among the various technologies in solving the intensifying energy crisis and environmental pollution,electrocatalytic conversion technology has attracted increasing attention as an efficient strategy due to its advantage in the direct utilization of sustainable and clean energy.Due to their large specific surface area,two-dimensional nanomaterials can provide more active sites in the electrocatalysis process,and thus exhibit better catalytic performance.Furthermore,the easily tunable electronic structure of two-dimensional nanomaterials has great made them potential candidates in the application of electrocatalysis.Therefore,this thesis explored the application of different two-dimensional nanomaterials in the field of electrocatalysis.This thesis aims to analyze the factors governing the performance of electrocatalysts and to achieve the improvement of the catalytic performance of two-dimensional nanomaterials by modulating the related factors.The authors obtained high-performance catalysts for nitrogen reduction reaction and carbon dioxide reduction reaction by improving the performance of Ni Fe layered double hydroxide and bismuth nanosheets through defect engineering and crystal phase modulation,respectively.This thesis provides a guideline for the preparation of high-performance catalysts,which include the following aspects:1.Rational design of catalytic sites to activate N?N is important to improve the nitrogen reduction reaction.A nickel-iron layered double hydroxide(V_o-Ni Fe-LDH)nanosheet catalyst with a high density of electron-deficient sites was constructed by introducing oxygen vacancies in the nickel-iron layered double hydroxide(V_oF-Ni Fe-LDH)under the guidance of theoretical calculations.The density functional theory calculation shows that the energy barrier of V_o-Ni Fe-LDH(0.76 e V)is much smaller than that of V_o-Ni Fe-LDH(2.02 e V).As a result,the performance of the electrocatalytic nitrogen reduction reaction of V_o-Ni Fe-LDH was significantly improved with an ammonia yield of 19.44?g h^-1 mg^-1_cat and a Faradaic efficiency of19.41%with excellent stability under the electrolyte of 0.1 M KOH,-0.2 V vs.RHE.This study not only provides an active electrocatalyst for the nitrogen reduction reaction but also provides a simple strategy for the design of catalysts for the nitrogen reduction reaction.2.The crystalline phase of two-dimensional nanomaterials determines the basic properties of the materials,and the synthesis method of two-dimensional nanomaterials largely determines the crystalline phase structure.Therefore,the controlled preparation of two-dimensional nanomaterials with specific crystalline phases is significant.We achieved the controlled growth of two-dimensional nanomaterials by different synthesis methods,leading to the synthesis of two-dimensional nanomaterials with different crystalline phases as catalysts:crystalline bismuth hydroxide(C-Bi(OH)₃)and amorphous bismuth hydroxide(A-Bi(OH)₃).The performance of A-Bi(OH)₃ is significantly higher than that of C-Bi(OH)₃ NSs for electrocatalytic carbon dioxide reduction reaction.Specifically,the Faradaic efficiency of formic acid is 94.9%(-1.1V vs.RHE)and energy efficiency is 52%(-1.0 V vs.RHE)with excellent stability in the H cell with 0.1 M KHCO₃ electrolyte.Besides,the Faradaic efficiency of formic acid was 99.5%(-1.2 V vs.RHE)and the energy efficiency was 68.5%(-0.3 V vs.RHE)with good stability in the flow cell with the electrolyte of 1 M KOH.In this study,not only the crystalline phase modulation was achieved through the controlled preparation of two-dimensional nanomaterials,but also the performance of electrocatalytic carbon dioxide reduction to formic acid was improved.