The Synthesis Of Petroleum Coke Derived Porous Carbon And Its Electrochemical Performance

With the rapid development of global economy in the last decades,worsening fossil energy depletion and global warming has made it imperative to develop clean,efficient and sustainable energy sources.In addition,the ever-growing demand from modern digital communications and electric vehicles or hybrid electric vehicles also promotes the development of alternative energy,as well as new energy storage devices with high energy density and power density.Among numerous energy storage devices,electrochemical capacitors,also being called supercapacitors?SCs?,have attracted considerable attention owing to their high power density,long lifespan and safe operation.In this dissertation,we reported the synthesis of a series of activated carbon with large surface area,hierarchical pore structure and controllable surface chemistry prepared from abundant petroleum coke?PC?.The influence of PC pre-oxidation by H₂O₂ and HNO₃ on the chemical activation process and surface chemistry of the resulting carbons were investigated.In addition,nitrogen species and oxygen-containing groups were also introduced into the activated carbon by post oxidation.The as-prepared carbon materials were used as electrode materials of supercapacitors.Their capacitive performance and hydrogen evolution performance in aqueous electrolyte were studied using a three-electrode system.Firstly,PC was used to prepapre activated carbon by a chemical activation with KOH.The influence of the mass ratio of KOH to PC on the microstructure,pore structure and surface chemistry of the porous carbons were investigated.With the increase of the KOH dosage,the activation process went through two main stages:pore-forming process and pore-enlarging process.The micropore surface area increased firstly and then reduced,while the mesopore surface area increased monotonously.The average pore diameter decreased firstly and then increased with the increase of the amount of KOH.The final prepared activated carbon possessed a high specific surface area(up to 2259 m²·g^-1),abundant mesopore content and good capacitive performance.Then,the influence of PC pre-oxidation by H₂O₂ and HNO₃ on the pore structure,surface chemistry and capacitive performance of the resulting carbons was studied.It was found that the pre-oxidation by HNO₃ had great influence on the physico-chemical properties of the porous carbons.The pre-oxidation process could reduce the activation difficulty and increase the mesopores and oxygen content,leading to easier electrolyte ions transports.Furtherly,oxygen-doping and nitrogen-doping were carried out using H₂O₂,HNO₃ and NH₃,respectively.The oxygen-containing groups could not only improve the electrochemical double layer capacitance,but also introduce pseudo-capacitance.The nitrogen species improved the wettability of the activated carbon in aqueous electrolytes,which was benifical for rapid ions transport.The as-prepared samples also presented excellent hydrogen evolution activities.Both oxygen-doping and nitrogen-doping could reduce the overpotential of hydrogen evolution reaction.In addition,hydroquinone groups were introduced into petroleum coke derived carbon by a simple physical adsorption method.The influence of reaction time,temperature and the amount of hydroquinone on the capactive performance of the samples were studied.The introduced hydroquinone groups provided large pseudo-capacitance,leading to an enhanced total specific capacitance.The specific capacitance of 300 F·g^-1 could be maintained even at a high current density of 50 A·g^-1.The energy density of the as-obtained sample could reach up to a high value of 19.5 Wh·Kg^-1 which was better than most of the previous carbons reported.