Preparation And Application Of Non-precious Metal Nanomaterials For Electrochemical Synthesis Of Ammonia

Ammonia is an important chemical raw material,widely used in industry and agriculture,as well as an important energy storage intermediate and carbon-free energy carrier.At present,the industrial ammonia synthesis is mainly based on Haber-Bosch process,which is not only high cost and energy consumption,but also seriously polluting environment.Electrocatalytic nitrogen reduction reaction?NRR?is a promising application technology,characterized by low cost and energy consumption,as well as no pollution on environment.Now the technology is still in its infancy,not only the ammonia yield is quite low,but also the selectivity is much poor.Therefore,electrochemical nitrogen fixation requires a catalyst with high activity and stability to promote the reaction process.To replace the Haber-Bosch process with electrocatalytic NRR,we have to think about the cost issues.Based on the analysis of the above mentioned problems for electrolytic NRR,we design and prepare a series of nonprecious metal oxides and phosphorus oxides,which exhibit excellent NRR activity and selectivity,as well as stability.This thesis mainly includes the following:?1?Preparation and performance of NiWO₄ electrocatalyst for the NRR.The catalyst is prepared by two-step method of hydrothermal reaction and thermal oxidation.The components and structure of the catalyst are determined to be porous nanobimetallic NiWO₄ by X-ray electron energy spectroscopy?XPS?,X-ray absorption near-edge structure?XANES?and?high-resolution transmission electron microscope?HRTEM technologies.The study on the relationship of structure and performance indicates that uniform porous structure and bimetallic synergy promote nitrogen adsorption,active site exposure and electrolyte transport.In acid medium,NiWO₄ exhibits excellent performance for the NRR,and the highest ammonia yield and FE are 48.86 ?g h-1 mg-1cat and 19.32% at the potentials of-0.5 V and-0.3 V?vs.RHE?,respectively.In neutral medium,the maximum FE reaches up to 10.18% at the potential of-0.3 V.?2?Preparation and performance of multi-component composite catalyst PC/Sb/Sb PO4 for the NRR.The precursor is prepared by mixing trimesic acid and antimony acetate,the resulted metal gel precursor is phosphate at high-temperature to obtain the catalyst.Benefiting from the integrated advantages of the active sites of PC and Sb PO4,as well as the three-dimensional honeycomb structure,the catalyst exhibits excellent NRR activity and selectivity in both acidic and neutral media.In an acid medium,its FE reaches 31% at the potential of-0.15 V.Meanwhile,in a neutral medium,the FE is about 34% at the potential of-0.1 V.The species evolution of the catalyst before and after NRR is studied through ex-situ XPS and XANES,indicating that PC and Sb PO4 are real active sites for the NRR,as well as the Sb0 is as the support to increase the exposure of the active sites.?3?Preparation and performance of phosphorus-doped carbon-supported zincphosphorus oxides for the NRR.The catalyst is prepared by phosphating a metal gel at high temperature pyrolysis,in which the metal gel is formed by mixing trimesic acid and zinc acetate solution.The multiple components synergetically and porous surface morphology of the catalyst improve the performance for the NRR.In an acid medium,the ammonia yield and FE achieves 24.7 ?g h-1mg-1cat and 17.4% at the potential of-0.2 V,respectively.