Study On Electrochemical Conversion Of Nitrate And Ammonia,and Its Application In Energy Storage

Nitrogen cycle is one of the most important element cycles in nature through organic nitrogen synthesis,ammonification,nitrification,denitrification,nitrogen fixation and other processes in living organisms accompanied by energy supply or release.These processes are involved in the growth and development of almost all living organisms.It is a long dream of chemists to realize the nitrogen cycle conversion process by artificially controlling and efficiently.In the past century,significant breakthroughs have been made in artificial nitrogen conversion technologies.However,most of these developed nitrogen conversion technologies require harsh reaction conditions,such as high energy consumption and serious pollution,which isn’t beneficial for green sustainable development.Therefore,how to use clean energy to achieve efficient nitrogen cycle conversion is still a major scientific problem.In addition,the nitrogen conversion process is usually accompanied by a large amount of energy storage or release,and the energy utilization involved in this process has not been paid much attention.Electrochemical technology can use solar energy,wind energy and other green energy to create a reaction environment where is like the biological nitrogen conversion process.The energy storage and release involved in the nitrogen conversion process can be controlled through electrons transfer,which is expected to realize the artificial controllable green nitrogen cycle process and efficient energy utilization.Therefore,this paper takes the electrocatalytic conversion reaction of nitrate and ammonia as the research object,and carries out some researches from green preparation of nitrate source,improvement of one-way conversion reaction efficiency,and application of reversible conversion of nitrate and ammonia in electrochemical energy storage.High overpotential,low selectivity and low current efficiency in the reaction can be improve through the design of efficient catalyst.Finally,the efficient forward and backward conversion of nitrate and ammonia was realized,and the potential application of the conversion reaction in the field of energy storage was successfully verified.The specific research contents are as follows:（1）The current industrial synthesis methods of nitric acid and ammonia are faced with high energy consumption and heavy pollution.Activating nitrogen by plasma technology coupled with electrochemical method which drived by the clean energy can realize the green preparation of nitric acid and ammonia.The activated air by electrically driven plasma is directly passed into the absorption solution.Nitric acid and nitrite are selectively synthesized by adjusting p H of the absorption solution.Nitric acid yield rate can reach 135 mg h^-1 when pure water as the absorption electrolyte.Also,plasma activated and electrochemical reduction process are combined to synthesize ammonia through a two-step process.（2）Study on electrocatalytic nitrate reduction to ammonia.For nitrate reduction to ammonia at high overpotential,this paper catalyzes nitrate reduction in two steps along[2+6]-electron pathway,which reduces the energy barrier of the reaction and improves its reactivity.Faradaic efficiency for synthetic ammonia is 100%at the lower potential of+0.1 V vs.RHE,and the energy consumption is as low as 17.7 k Wh kg^-1.（3）In the research work of this chapter,the process of ammonia oxidation to nitrate was explored and studied systematacially by using high activity Cu O nanosheet catalyst.NO_x^-（x=2,3）Faradaic efficiency is as high as 99.2%at 1.5 V vs.RHE,which confirmed the successfully achievement of the oxidation of ammonia to nitrate.Finally,the conversion process of ammonia oxidation to nitrate was explored by in-situ infrared technology and confirmed that ammonia oxidation is a stepwise dehydrogenation and oxygenation process,providing the guidance further understanding in depth of ammonia oxidation process.（4）Combined with nitrate reduction and ammonia process.The efficient bidirectional conversion of nitrate and ammonia was realized through the designing and preparing of Ni Ru Janus catalysts and Zn-Zn²⁺//NO₃^--NH₃ secondary battery（zinc-nitrogen battery）was assembled,which successufully realized the application of electrochemical energy storage.Zinc-nitrogen battery with an actual energy density of 577 Wh L^-1 have achieved 930charge-discharge cycles（12.9 days）.