Capacitance Performances Of Rice Husk Based Porous Carbon With Superlyphilicity

Supercapacitors have emerged as promising candidates for energy storage due to their outstanding power density,long cycling stability and fast charge/discharge characteristics.To date,a lot of efforts have been devoted to increase the energy density of supercapacitors by increasing the specific capacitance?C?using novel electrode materials.Among them,hierarchical porous carbon materials derived from biomass,which possess micropores?<2 nm?,mesopores?2-50 nm?and macropores?>50 nm?,have received extensive attention,concentrating on the multiscale architecture synergistic effect,easy accessibility and relatively low cost.However,most biomass-derived carbon materials suffer from poor lyophilicity and surface area availability,resulting in low capacitance and charge-discharge rates.Using the self-template structure of rice husk,a series of hierarchical porous carbon materials were prepared through chemical activation.The effects of single activating agent and mixed activating agents on the wettability,porosity,and chemical composition of carbon materials were studied.Various electrochemical properties of different lyophilic rice husk based porous carbon in acidic electrolytes were systematically studied and their actual application prospects was studied.Finally,the corresponding capacitive properties of superlyophilic rice husk-based porous carbon in organic electrolytes were studied.The specific research results are as follows:?1?We propose an efficient method for the preparation of superlyophilic rice husk-based porous carbon with micro/nano hierarchical structure.The preparation process of rice husk-based porous carbon includes carbonization,NaOH-leaching and chemical activation.In this paper,NaOH,KOH and a specific mixture of the two were used as activating agents.NC-3,KC-3 and NKC-3 were selected as representative carbon samples for a series of physical characterizations.The results of nitrogen adsorption/desorption tests showed that among the three carbon materials,NKC-3 had the largest specific surface area(2747 m² g^-1),wider pore size distribution,and highly developed porosity.XPS test results show that NKC-3 not only has the highest oxygen atom doping amount?9.86%?compared with NC-3 and KC-3,but also has the largest proportion of hydroxyl groups in the surface oxygen-containing functional groups.In the static contact angle test,only the contact angle between NKC-3 and 1M H₂SO₄ was less than 5°,and reached superlyophilicity.The above results indicate that the rice husk-based carbon material prepared by co-activation has supelyophilicity and high porosity,which lays the foundation for its subsequent energy storage application.?2?The electrochemical properties of rice husk-based porous carbon in acidic electrolytes were investigated.Three types of carbon materials,NC-3,KC-3,and NKC-3,were used as active materials of electrodes,and 1M H₂SO₄ was used as the electrolyte to assemble a symmetric supercapacitor.In the cyclic voltammetry test,the rectangular integral area of the NKC-3 is the largest at the same scan rate,indicating that the maximum energy storage is achieved.At a scan rate of 5 mV s^-1,the specific capacitance of the NKC-3 is 199.4 F g^-1.Electrochemical impedance spectroscopy results show that NKC-3 has the lowest equivalent series resistance,charge transfer resistance and diffusion resistance among the three,which is due to the superlyophilicity and high porosity of NKC-3.In the galvanostatic charge-discharge test,the specific capacitance of NKC-3 was 194.6 F g^-1 when the current density was0.5 A g^-1,which was much higher than that of NC-3 and KC-3.And when the current density increased to 20 A g^-1,the specific capacitance of NKC-3 only decreased by14.1%,indicating that NKC-3 has excellent rate capability.After 10000 cycles of galvanostatic charge-discharge,the retention of specific capacitance was 95.6%,demonstrating excellent cycle stability.These outstanding electrochemical properties manifest that NKC-3 carbon materials are very promising high-performance supercapacitor electrode materials.?3?The electrochemical performance of superlyophilic rice husk-based porous carbon in organic electrolyte was studied.The static contact angle test results show that NKC-3 is superlyophilic to 1M Et₄NBF₄/PC solution.With 1M Et₄NBF₄/PC as the organic electrolyte,the electrochemical performance of the NKC-3 based supercapacitor under two-electrode system was tested.The cyclic voltammogram profiles of NKC-3 still maintain quasi-rectangular shape as the scan rate increases from 5 mV s^-1 to 20 mV s^-1,realving obvious double layer capacitance characteristics.In the galvanostatic charge-discharge test,the specific capacitance of NKC-3 at a current density of 0.5 A g^-1 is 138.3 F g^-1,which is still 88.1%at 20 A g^-1,indicating that NKC-3 has a good rate characteristics.After 10000 cycles of galvanostatic charge and discharge,the specific capacitance of NKC-3 dropped by only 11.1%,with outstanding cycle stability.Electrochemical impedance spectroscopy shows that NKC-3 has a small charge transfer resistance and can ensure rapid electron transfer.When the power density increases from 310.5 W kg^-1 to 10523.1 W kg^-1,the energy density of NKC-3 only decreases from 29.5 W h kg^-1 to 19.0 W h kg^-1.The smaller energy loss shows that NKC-3 based supercapacitor can be used for high power storage and output.