Pseudocapacitive Performance And Charge Storage Mechanism Of Nitrogen-containing Conjugated Organic Molecules

Design and manufacture of high performance electrode materials and increase energy density while maintaining high power density have become the development direction of pseudocapacitors.Nitrogen-containing organic electrode materials are potential energy storage materials.It is particularly important to clarify the charge storage mechanism of nitrogen atoms in nitrogen-containing organic electrode materials for the design of pseudocapacitor materials.In this paper,we intend to design and synthesize nitrogen-containing conjugated organic molecules with specific nitrogen configurations.Through theπ-πinteraction of delocalized electrons,the nitrogen-containing organic molecules are stacked in a single layer parallel on a carbon substrate with high specific surface and high porosity to construct the organic small molecule/porous carbon model electrode material with C=N active center.The internal relationship between organic molecule arrangement and electrochemical performance of carbon material was revealed,and the electrochemical performance of monolayer parallel stacking was better.Further,the redox reaction mechanism and charge storage mechanism of specific nitrogen in nitrogen-containing conjugated organic molecules were explored,and asymmetric supercapacitors with high energy density and high power density were constructed.It provides a theoretical basis for studying the energy storage mechanism of nitrogen-containing organic molecules.PZ/HPC and Phen/HPC composites were constructed by stacking phenazine（PZ）-Phenanthroline（Phen）on porous carbon with few parallel layers throughπ-πinteraction of delocalized electrons.The stacking and arrangement of organic molecules on the surface of porous carbon and pore channels are studied to elucidate the single-layer parallel stacking process and mechanism.PZ/HPC is a surface-controlled pseudocapacitor charge storage kinetics.The serrated pyridine nitrogen of phenoazine molecule can undergo a surface redox reaction with cationic（K⁺）coupled electron transfer.The theoretical capacity is 1073 C g^-1,and the reaction is one step and two electrons.30%PZ/HPC specific capacitance of 558 F g^-1(0.2A g^-1),100 A g^-1 capacitance retention rate of 43%,at 10 A g^-1 current density of 20000cycles of capacitance retention rate of 88%.Assembled into asymmetric supercapacitors,the extended voltage is up to 1.4 V and the mass energy density is 19.7 Wh Kg^-1,much higher than traditional carbon materials.In order to further improve the specific capacitance,the structure of the molecule was designed.Multiple active centers of C=O and C=N were introduced to prepare TAPQ with a theoretical capacity of 1855 C g^-1.TAPQ/HPC was prepared by stacking TAPQ on porous carbon with fewer layers and parallel layers.C=N and C=O are the electrochemical active centers,and cationic（K⁺）coupled electron transfer can occur on the surface REDOX reaction,which is a six-electron reaction process.In the alkaline electrolyte,the specific capacitance of30%TAPQ/HPC is 633 F g^-1(0.6 A g^-1),and the capacitance retention rate is only 36%at the current density of 2 A g^-1 for 10000 cycles.Due to the deep reduction product dissolves in the electrolyte,the cycle stability is not good.The cycle stability is improved by controlling voltage window and constructing layer structure.In the 0.8 V voltage window,the capacitance retention rate is increased to 81%after 10,000 cycles at 2 A g^-1 current density.A two-step deposition method was used to deposit reduced product-stabilized phenazine on the outer layer of TAPQ with a structural layer/layer structure.The specific capacitance of 30%-TAPQ:PZ=2:1/HPC was 463 F g^-1(0.6 A g^-1)under a voltage window of 1 V.At the current density of 2 A g^-1,the capacitance retention rate of 10000 cycles is 64%.Assembled into asymmetric supercapacitors,extended voltage to 1.4 V,mass energy density of 22.4 Wh Kg^-1,14%higher than 30%PZ/HPC.