Fabrication Of Biomass-derived Heteroatom-doped Porous Carbon Materials And Electrochemical Performance For Supercapacitors

Electrical double-layer capacitors?EDLCs?,as new type of energy storage device,have drawn extensive attention because they can instantaneously offer a high power density and long cyclic life,which make them promising for applications such as consumer electronics,aeronautics and astronautics,track traffic and military equipment.Porous carbon have been widely explored as electrodes materials for EDLCs because of advantages of large specific surface area?SSA?,abundant porosity and low resistivity.However,EDLCs suffer from a low energy density;simultaneously reducing its production costs is imminent.Therefore,developing high-performance and low-cost porous carbon electrodes is one of main topics for EDLCs research.We have tried design and construct the microstructure?SSA?pore and morphology?of electrodes to prepared heteroatom-doped nanostructured porous carbons derived from low-cost biomass,exploring the relationships between electrodes structure and electrochemical performance;and constructed high-power and long-life symmetric EDLCs devices,using the wide voltage of electrolyte to improve the energy density.?1?We developed a general approach to prepare N-doped ultrathin porous carbon nanosheets with abundant crumples structure based on Schiff-base polymers by molten salt-based chemical activation?KOH@LiCl/KCl?.Using molten salt-activation can realize the morphology design and pore regulation of carbon materials,and LiCl/KCl can be recycled after recycling.The 2D structure provides shorten the ion-diffusion length;large amounts of mesoporous structure guarantees fast diffusion of electrolyte ions,increasing utilization of the SSA;and the crumples structure avoids self-stacking between layers and makes efficient use of micro/mesopores.ACS-7 electrode exhibited a maximum capacitance of 243 F g^–1(37?F cm^-2)at 0.5 A g^–1 in 6M KOH electrolyte,high rate capability(179 F g^–1 at 20 A g^–1)and outstanding cycle stability.?2?We used natural sepia ink as a sustainable source to synthesize nitrogen-rich highly porous carbon nanospheres by a simple molten salt-based activation strategy.The introduction of molten salt?LiCl/KCl?is not only beneficial for repairing the carbon conjugate networks,but can also further improve the activation effect of porogen?KNO₃?,enhancing the SSA and mesopore ratio.The as-obtained carbon nanospheres displayed a large SSA of 1760 m² g^–1 and high N content?8.6 wt%?.It has been demonstrated N doping can efficiently enhance charge transfer and surface wettability,and inducing favorable pseudocapacitance.With this design,MA-NCS electrode exhibited a remarkable specific capacitance of 320 F g^–1 at 0.5 A g^–1 and high rate capability(225 F g^–1 at 30 A g^–1)in 6M KOH electrolyte.Furthermore,the assembled EDLCs demonstrated a specific capacitance of 130 F g^–1 at 0.5 A g^–1 in 1M TEABF₄/AN electrolyte,exhibiting maximum energy density(28.2 Wh kg^–1)and power density(37.7 kW kg^–1).?3?We developed a simple and general silica-assisted strategy for fabrication of free-standing interconnected 3D meso-microporous carbon nanofiber networks by confine nanospace pyrolysis of sustainable bacterial cellulose?BC?.The procedure can lead to the additional development of SSA and mesoporosity,which attributed to a self-activation process occurring in the nanoreactor;it also indicated that using this method to develop porosity does not damage graphitization degree.The synthesized carbon nanofibers exhibited the features of interconnected 3D networks architecture,large SSA and mesopores-dominated hierarchical porosity.With this design,CN-BC electrode displayed a specific capacitance of 302 F g^–1(48.4?F cm^-2)at 0.5 A g^–1,high rate capability(193 F g^–1 at 20 A g^–1)and good cyclicity in 6M KOH electrolyte.?4?In this work,sustainable BC is used both precursor and bio-template for facilely synthesis of free-standing N,S-codoped?N:3.1 at%;S:3.2 at%?3D porous carbon networks by the pyrolysis and activation of polyrhodanine coated BC.The modification strategy of doping and activation can achieve optimal regulation of SSA,pore structure and interface properties.The synthesized carbon networks show a large SSA(1420 m² g^-1)with hierarchical meso-microporosity,and interconnected continuous networks can facilitate fast ion/electron transport along 3D directions.Benefit from these,a-NSC as binder-free electrode exhibits a high specific capacitance of 340 F g^-1 at 0.5 A g^-1 in6M KOH electrolyte and high rate capability(71%at 20 A g^-1).Moreover,the assembled symmetrical EDLCs display a much short time constant of 0.35 s in 1M TEABF₄/AN electrolyte,obtaining a maximum energy density of 32.1 Wh kg^-1;and show an excellent circulation with 94%retention after10000 cycles at 2 A g^-1.