Strategically Increasing The Efficiency Of Electrocatalytic Ammonia Synthesis Under Ambient Contditions

Ammonia is one of the most demanded inorganic compounds in the world so far,and it has important applications in agriculture,medicine,military industry,chemical industry and other fields.Now Haber process is profoundly changing the world,about 48%of the world's population is now fed by the increased grain production of Haber process.Active nitrogen is an important part of cell's DNA and RNA.Some important nutrients such as peptides,amino acids,and vitamins can also be artificially modified and synthesized.With the development of the Haber process for ammonia synthesis,nitrogen-containing explosives such as ammonium nitrate,nitroglycerin,trinitrotoluene,etc.have been synthesized in large quantities for defense and infrastructure construction.Many previously expensive or rare compounds such as synthetic fibers,synthetic resins,Dyes,etc.can also be mass produced.Ammonia is a clean carbon-free liquid fuel,and it can store hydrogen energy efficiently,its bulk energy density is 1.5 times that of liquid hydrogen,the liquid form of it also helps it to be transported in large quantities through tanks or pipelines.Haber process requires high-temperature and high-pressure reaction conditions,which depends on depleting fossil feedstocks,and is accompanied by significant CO₂ emissions.However,electrochemical ammonia synthesis is a very promising way,it does not require high-temperature and high-pressure.It can be performed under ambient conditions,and It does not require a high-level infrastructure.It is scalable and can be conveniently combined with renewable energy to form a decentralized grid layout,especially for areas with poor infrastructure.But nitrogen is a non-polar inert gas,and its solubility in water is extremely low.Nitrogen reduction at negative potentials also encounters competitive hydrogen evolution reactions,which can lead to very low Faraday efficiency.It is clearly not enough to address the above problems only from a catalyst perspective.Therefore,this thesis proposes some novel solutions and strategies from various aspects,and we experimentally and theoretically investigated the effective ways of enhancing ammonia production and Faraday efficiency.The specific research content as follows:?1?Inspired by the the physical gills of a water spider for the first time,we construct a bionic hydrophilic-hydrophobic heterojunction on the electrode.The combination of hydrophilic carbon sphere and hydrophobic ultrathin porous Bi₅O₇I nanotube effectively builds a stable gas-liquid-solid three-phase interface,improving the solubility of nitrogen near catalyst,enhancing ammonia yield and Faradaic efficiency.Inspired by the behavior of hemagglutinin to transport oxygen for the first time,we added the aerophilic ultrathin porous Bi₅O₇I nanowire in electrolyte.The ultrathin porous Bi₅O₇I nanotube suspended in the electrolyte increase the transfer rate of nitrogen and playes a role of cocatalyst.Theoretical calculations show that the enzyme-catalyzed reaction pathway with a side-on configuration has a low reaction energy barrier.From the perspective of electrode and electrolyte,this chapter provides a new strategy for improving ammonia yield and Faraday efficiency.?2?Inspired by the selective permeability of cell membrane for the first time,we studied the relationship between pore area of membrane and Faradaic efficiency.Under the conditions of a physical model based on a plate capacitor,a function of the dielectric constant of the electrolyte and the electric field near the electrode surface is deduced.The relationship between Faraday efficiency and H⁺transfer rate used for hydrogen evolution are established by a mathematical model,and getting a good fit with the experiment value.FeAg nanoclusters supported on silicon nanowire were synthesized by a rapid heating and rapid quenching method.The surface plasmon-enhanced FeAg nanoclusters has a high catalytic activity,which can convince the results effectively.The theoretical calculations show that the closer the distance between Fe atoms in FeAg nanoclusters the stronger their adsorption capacity for nitrogen molecules.We present a new strategy for the continuous regulation of Faraday efficiency by regulating the hydrogen ion transfer rate,which can be easily applied to most of the current catalytic systems with almost unlimited accessibility,opening up a new way for further research on nitrogen reduction.?3?The efficiency of electrocatalytic ammonia synthesis is not only limited by the activity of cathode,but also by the activity of the anode.The cotton is dissolved at low temperature,iron and nickel salts were then added to the dissolved cellulose and subjected with hydrothermal reaction,freeze drying and secondary calcination.Finally,the mesh carbon loading Fe₅Ni₄S₈ is successfully prepared,which has lower over potential and charge transfer resistance.The improvement of its activity comes from the interaction between 3d orbital electrons of Fe and Ni atoms,which increases the d-band center of Fe atoms and reduces the d-band center of Ni atoms,improving the whole catalytic activity.This chapter provides a new strategy for designing high-performance catalyst for oxygen evolution.