Electrochemical Performances Of Redox Electrolyte Mediated Super Capacitors

Pseudocapacitance in supercapacitor is commonly originated from the reversible redox reactions of electrode materials such as N-doped porous carbon and transition metal oxides,therefore contributed significantly to the overall energy storage capacity when used as electrochemical electrode materials.Despite this,the pseudocapacitance of electrode material itself is still limited.The incorporation of redox active species in electrolyte is a promising approach to profoundly enhance the device capacity of a supercapacitor.In this thesis,the electrochemical performances of supercapacitors in redox electrolyte systems were focused.N-doped porous carbon and transitional metal oxides were attempted as electrode materials,and polyphenol and K₃Fe?CN?₆ were introduced into the electrolyte system.Promoted by the catalytic activities of electrode materials,the rapid and reversible redox reaction of redox active species in electrolyte were occurred,hence,improved charge storage performance of the resultant supercapacitor were accomplished.The main content involves the following aspects:?1?Graphene incorporated,N doped activated carbons?GNACs?were synthesized by alkali activation of graphene-polypyrrole composite?G-PPy?at different temperatures.Under optimal activation temperature of 700?,the resultant samples,labeled as GNAC700,owns hierarchically porous texture with high specific surface area and efficient ions diffusion channels,N,O functionalized surface with apparent pseudocapacitance contribution and high wettability,thus can deliver considerable capacitance,a high rate capability and a good cycle ability when used as supercapacitor electrode.Furthermore,pyrocatechol was incorporated into the acidic electrolyte system,the GNAC700 electrode demonstrates high catalytic activity for the redox reaction of pyrocatechol/o-quinone pair in H₂SO₄ electrolyte,thus enables a high pseudocapacitance from electrolyte,which is directly associated with the pyridinic N species in the N doped carbon material.Under optimal pyrocatechol concentration in H₂SO₄ electrolyte,the electrode capacitance of GNAC700 increased by over 4 folds to 512 F g-1 at 1 A g-1.Pyridinic-N was deemed to be responsible for the high catalytic activity.This work provided a promising reference to ameliorate the capacitive performances of supercapacitors by the synergistic interaction between redox-active electrolyte and catalytic electrodes.?2?Network shaped graphene-NiO hybrids deposited onto nickel foam were prepared by hydrothermal deposition followed by annealing at low temperature,the hybrid can offer a specific capacitance of 1058 F g-1 1A g-1 in alkaline electrolyte.Moreover,the electrode exhibited high catalytic activity on the redox reaction of K₃Fe?CN?₆ in alkaline electrolyte,therefore,a much higher specific capacitance of 3790 F g-1 at 1 A g-1 was achieved via the dual redox contributions of electrode and electrolyte,and a high rate capability was simultaneously achieved,the additives and high catalytic activity between the electrode and electrolyte,showing prominent enhancement of energy storage performance of catalytic electrode.?3?The N-doped carbon material with special crosslinked hollow sphere was synthesized by polymerization of aniline monomer in aqueous system with existence of oxide graphene,followed by the pyrolysis of precursors.The as-formed N-doped carbon framework can provide good capacitive character and catalytic activity and it can provide good capacitive property in conventional acidic electrolyte.Under optimal polyphenol concentration in H₂SO₄ electrolyte,the electrode capacitance increased by over 2 folds to 340 F g-1 at 1 A g-1.The electrode was also tested in different temperature,showing great potential in electrochemical energy storage.