Study Of Preparation Of Nitrogen-rich Porous Carbns Based On Cross-linked Polymers And Their Supercapacitive Performance

Supercapacitors are a new type of energy storage device,which can be charged/discharged through electrostatic adsorption/desorption on the surface of electrodes.They have been receiving extensive research interests due to their extraordinarily high power density,excellent cyclic stability and safety.Electrodes are the primary component and thus determine the performance of supercapacitors.Currently,carbonaceous materials are the most widely studied electrode material,yet their performance still need to be improved.In this thesis,a highly cross-linked polymeric network was designed and synthesized,which was then carbonized and activated with KOH to prepare porous carbons.The morphology and microstructure of the carbons was facially controlled through such a method.The capacitive performance of the porous carbons was systematically investigated.Furthermore,the two-dimensional hierarchical porous carbon?2D-HPC?were used as electrodes to construct flexible supercapacitors,which led to excellent performance.The results are detailed below.P-phenylenediamine and acet aldehyde were reacted through condensation which resulted in a highly cross-linked poly?p-phenylenediamine-aldehyde??PDAA?resin.The PDAA resin was then mixed with KOH with different ratios and treated at 800°C to prepare a series of nitrogen-rich hierarchical porous carbons,which are denoted as PDAA-CKn?n=0,1,2,3?.The chemical state,morphology,microstructure,surface area and pore size distribution were systematically investigated using various techniques.It was found that the wall thickness of the pores decreases with the increase of KOH:PDAA ratio.Honeycomb-like structure specific surface area of 2406 m²/g was formed at a KOH:PDAA mass ratio of 1:3?PDAA-CK3?.The porous carbons were used as electrodes to construct coin-cell type supercapacitors and the electrochemical performance was evaluated.Moreover,we systematically investigated the electrochemical properties of all the porous carbons in 6M KOH,1M NaSO₄and ionic liquid EMIMBF₄ electrolyte,respectively.It was found that those porous carbon based supercapacitors show the best performance when using the 6M KOH electrolyte.As the n increased,the capacitance of the porous carbons increased.PDAA-CK3 has the capacitance of 280 F/g at the current density of 0.5 A/g,and is typical of electrical double layer capacitance.When EMIMBF₄ electrolyte was used,the potential window can be extended to0-4 V?the devices can be only operated under 0-1 V when using aqueous electrolyte?.PDAA-CK3 exhibited the best performance among all the PDAA-derived carbons,showing an energy density of 139 Wh/kg at a power density of 500 W/kg with an ionic liquid EMIMBF₄ as the electrolyte.The highest power density was 9536 W/kg and the corresponding energy density was 102 Wh/kg.Furthermore,flexible supercapacitors were prepared using PDAA-CK3 as the electrode and both EMIMBF₄ and KOH as the electrolytes,the device with the 6M KOH electrolyte shows an even higher capacitance.At a current density of 0.5 mA/cm²,the capacitance was298 mF/cm²,and when at a current of 10mA/cm²,the capacitance was still 196 m F/cm².At both current densities,the Columbic efficiencies were higher than 95%.The capacitance retention was 87%after being bent for 2500 cycles,showing excellent flexibility when using an aqueous electrolyte.On the other hand,the device with the EMIMBF₄ electrolyte exhibited extraordinary volumetric capacitances,being 51.1 F/cm³ at 0.42 A/cm³.The capacitance retention was 96%after 10000 cycles of charge-discharge at the un-deformed state.In addition,the device also exhibited super-high energy density of 27.2 m Wh/cm³ at a power density of 80 mW/cm³ and a retained value of 17.4 mWh/cm³at a power density of 1.6 W/cm³.The capacitance retention was still retained 78%after 10000 cycles of bending-unbending.