Application Of Carbonyland Imine Organic Compounds In Decoupled Water Electrolysis

With the development of the economy and the growth of the population,the energy crisis has become a major challenge facing our society.At present,fossil fuels are still the main body of the energy mix.In the face of the environmental and energy structure problems associated with the large-scale use of fossil energy,changing the current unreasonable energy structure dominated by fossil energy has become an inevitable choice.Therefore,it is of great significance to develop green and environmentally friendly new energy sources to replace fossil fuels.Due to its high energy density(140 MJ kg-1)and zero CO2 emissions,hydrogen is the ideal alternative energy source and the most promising potential energy source.At present,more than 90% of hydrogen production comes from fossil fuels,which not only consumes a lot of non-renewable energy,but also increases greenhouse gas emissions.However,conventional water electrolysis may be affected by gas mixing,and the different kinetics of hydrogen evolution and oxygen evolution reactions will limit the direct use of unstable renewable energy sources and increase the cost of hydrogen production.In recent years,with the utilization of solid redox media,the concept of decoupling water electrolysis has been proposed,which can separate hydrogen and oxygen produced in different times and spaces without using membranes.Therefore,in order to achieve an efficient hydrogen production system,solid redox media with low cost and high performance need to be developed.Based on this,this paper studies several different organic solid-state redox pairs,applies them to electrolyzed water systems,and combines them with renewable energy to realize the step-by-step production of hydrogen and oxygen.The main research contents are as follows:(1)Hex-Aza,a novel layered polymer based on hexaketocyclohexane was designed and constructed by multi-step solvothermal condensation reaction.The newly synthesized redox-functionalized Hex-Aza shows a higher specific capacity.At a current density of 2 A g-1,the specific capacity can reach 144 m A h g-1.After 2600 cycles of charge and discharge at a current density of 5 A g-1,the capacity retention rate is 49%.Therefore,using Hex-Aza as a solid redox medium,a membrane-free decoupling acid electrolyzed water system was developed.(2)In the previous section,we successfully synthesized an ideal organic compound for step-by-step electrolysis of water to hydrogen production.However,the preparation process of Hex-Aza is more complicated.Thus,in this chapter,we synthesized diquinoxalino [2,3-a:2’,3’-c]phenazine(HATN)using a simple one-step solvothermal solution.Multiple electroactive pyrazine units in HATN can provide high capacity capacity.In addition,π conjugated aromatic structures facilitate charge transport across the electrode and enhance structural stability during proton insertion/removal.At a current density of 0.5 A g-1,the reversible capacity of the HATN electrode is 290 m Ah g-1.In addition,the HATN electrode has a capacity retention rate of 51% and a coulombic efficiency of 100% after 3000 cycles at a current density of 5 A g-1.The testing of the decoupled electrolysis of water to produce hydrogen system based on HATN at different currents shows that the system can adapt to the intermittency and volatility of renewable energy.After 500 consecutive alternating electrolytic cycles,the O2 generation voltage and H2 generation voltage remained stable,indicating that the HATN-based decoupling device showed good stability under fluctuating current.In addition,we couple photovoltaic panels with HATN-based decoupling devices to build a photovoltaic water electrolysis system.(3)The previous part for the first work,both the specific capacity and stability have been improved,however,the dissolution of organic matter in the electrolyte is inevitable.Therefore,in order to further improve the stability of organic matter during charging and discharging.In this section,we use spherical poly(quinone amine)nanoparticles(PQANPs)synthesized by simple precipitation polymerization as solid redox media materials for step-by-step electrolysis of water.PQANPs have excellent electrochemical performance,ultra-fast rate capability of 104 m Ah g-1@20 A g-1,and an ultra-long cycle life of 7124 cycles.At a current density of 1 A g-1,the reversible capacity of the PQANPs electrodes is 218 m Ah g-1.In addition,the PQANPs electrodes have a capacity retention rate of 67% and a coulombic efficiency of 100%after 7124 cycles at a current density of 5 A g-1.Decoupled electrolysis of water to produce hydrogen system based on PQANPs can also work under different currents and has good cycle stability.