Preparation And Capacitive Performance Of Nitrogen-rich Hierarchical Porous Carbons

Supercapacitors(SCs)are novel energy storage devices with high capacity,high power density,long cycle life and and fast charge/discharge capabilities.Among the most versatile supercapacitor material,porous carbon has attracted significant attention due to its low-cost,larger surface area,high conductivity and robust stability.In this context,the present study explores the possibility of sucrose and phenolic resin as precursor carbon sources,nitrogen-containing organic salts as nitrogen sources,hard templates and activation agents to produce nitrogen-rich hierarchical porous carbon materials for supercapacitors.The catalytic mechanism of organic salt on the carbon graphitization process is also investigatedSucrose-based porous carbon was prepared using an inert atmosphere pyrolysis approach(700-950?)with zinc salt of disodium ethylenediaminetetraacetate(EDTANa2Zn)concurrently used as nitrogen source,hard template and activation agent.The experimental results indicated increased association of surface area with carbonization temperatures whereby,the nitrogen context was observed to decrease.At 700?,the nitrogen content of 5.67%was measured besides the largest specific capacitance of 283 F g-1 recorded in 6 mol L-1 KOH alkaline electrolyte.However,the largest specific surface area of 2160 m2 g-1 was achieved at 950?.The sucrose derived nitrogen-rich porous material based on high surface area,dense surface porosity(2.034 cm3 g-1)exhibited excellent rate performance with retained specific capacitance of 84.5%at 300 A g-1.Phenolic resin/EDTANa2Zn salt composites were prepared by solid phase ball milling approach and then carbonized under inert atmosphere at high temperature(700-1200?).The phenolic resin(PF)served as carbon source while EDTANa2Zn salt concurrently functioned as nitrogen source,hard template,activation agent and graphitizing agent.A superior phenolic resin-based nitrogen-rich hierarchical porous carbon material with high specific surface area(2484 m2 g-1)and pore volume(1.546 cm3 g-1)was obtained at optimum temperature of 800?.The degree of graphitization was also studied against carbonization temperature.A gradual rise in the degree of graphitization was evident with the rise of carbonization temperature with maximum graphitization(IG/ID=1.72)observed at 1200?.The electrochemical characteristics of the prepared material were evaluated both in aqueous and organic electrolyte system.The porous carbon material prepared at low-temperature(700?),possessed large specific surface area and high nitrogen content with the maximum specific capacitance of 270 F g-1 in 6 mol L-1 KOH alkaline aqeous electrolyte.In contrast,the porous carbon prepared at high degree temperature(1200?)inherited high degree of graphitization and excellent rate performance in 1 mol L-1 Et4NBF4/PC organic electrolyte conditions.In the view of elaborate experimental investigations,it was evident that EDTANa2Zn salt influences the degree of graphitization in nitrogen rich porous carbon material and can be used as catalyst for carbon graphitization.The mechanism deduced after careful experimentation infer to the contribution of nano sized zinc oxide and sodium carbonate formed subsequent to high temperature pyrolysis of EDTANa2Zn salt.To further confirm this,zinc oxide/phenolic resin and sodium carbonate/phenolic resin based carbon material were prepared in similar fashion.The degree of graphitization in case of sodium carbonate/phenolic resin carbon(IG/ID=1.43)was noted to be relatively higher than zinc oxide/phenolic resin carbon(IG/ID=0.78).Further study confirmed that sodium carbonate can accelerate the graphitization of phenolic resin to a certain extent at 1000?.