Preparation And Energy Storage Performance Of Lignocellulose-based Porous Carbon

Under the background of increasingly energy and environmental issues,the development of renewable energy has become an important link to achieve the goal of"carbon neutrality".As a kind of agricultural waste with huge output.rice husk is generally incinerated at present,.This treatment method not only damages the air quality of surrounding areas,but also causes the waste of natural resources.Recently,lignocellulose-based porous carbon prepared from rice husk has attracted the attention of researchers because of its low cost and rich pore structure.It is widely used as electrode materials for energy storage devices,like supercapacitors.However,rice husk-based porous carbon will acquire a large number of oxygen-containing groups imported from the activation process,resulting in serious leakage current and self-discharge.This reduces the energy storage efficiency of supercapacitors.In addition,although rice husk-based porous carbon shows good electrochemical properties in laboratory research,its electrochemical performance under low mass loading is far from evaluating its practical application value.Herein,the problems of high leakage current and serious self-discharge are solved through the chemical modification of lignocellulose-based porous carbon,which plays an important role in improving the energy storage efficiency of biomass-based carbon electrode.Aiming at the problem of performance degradation caused by the transition from laboratory-grade mass loading to commercial-grade mass loading,high mass-loading lignocellulose-based porous carbon electrode materials with excellent electrochemical properties were prepared,which explored the effects of different activation atmospheres on the electrochemical properties.This research provides useful exploration for the practical application of biomass-based porous carbon in supercapacitors.The main research results are as follows:1.High-performance armor-wearing lignocellulose-based capacitor carbon（NP-RHPC）was prepared with finely adjustable surface properties and micro-structure using rice husk as carbon source and coal pitch as chemical modification reagent.The synergetic effect of the stable biochar skeleton and the pitch carbon armor ensures NP-RHPC has low leakage current and self-discharge,long cyclic stability,and good rate performance.The normalized leakage current of NP-RHPC is only 40.9μA F^-1 after constant voltage charging for 2 h,and the open circuit voltage attenuation rate is 28.27 m V h^-1,which is better than that of N-RHPC without pitch carbon armor(52.2μA F^-1,37.33 m V h^-1)and commercial capacitor carbon YP-50F(42.5μA F^-1,30.44 m V h^-1).Furthermore,the synthesized NP-RHPC has ideal specific capacitance of 209.2 F g^-1 and the capacitance retention rate is up to95.0%over 20000 cycles at a high current density of 1.0 A g^-1,which is higher than that of N-RHPC.This impressively long-term cyclic performance of NP-RHPC can be ascribed to the excellent electrical conductivity and especially the reduction of the unstable oxygen-containing groups.This study provides insights for the rational design of high-performance armor-wearing biomass-based porous carbon electrode material towards the advanced application of biomass and coal pitch in energy storage.2.The effects of reaction atmosphere on yield and the electrochemical properties of lignocellulose-based porous carbon were systematically studied.The carbonization and desiliconization yields of lignocellulose do not have significant difference in air and inert atmosphere.However,when the chemical activation process was employed in inert atmosphere,N-RHPC has higher yields.N-RHPC-Ar has the highest total yield of 23.2%,and the yield of N-RHPC-Air was only 9.5%.In addition,N-RHPC can achieve higher capacitance with chemical activation in inert atmosphere.The specific capacitance of laboratory-grade mass-loaded N-RHPC-Ar in the 6 M KOH two-electrode system at 0.5 A g^-1 is 347.3 F g^-1,which is higher than that of N-RHPC-N₂,while N-RHPC-Air is only 274.1 F g^-1.Increasing the mass load of electrode will make the N-RHPC have lower self-discharge rate and higher leakage current.Furthermore,the capacitance value of N-RHPC is also difficult to reach the original level.When the mass loading of the electrode material is 11.4 mg cm^-2,the mass specific capacitance of N-RHPC-Ar is 274.1 F g^-1,and the corresponding surface capacitance is 3.2 F cm^-2,which have significant advantages in biomass-based carbon materials for supercapacitors.Among the three reaction atmospheres investigated,N-RHPC has similar voltage retention.The N-RHPC prepared in Ar atmosphere has lower leakage current.This study provides a new idea for the efficient utilization of biomass-based porous carbon in supercapacitors.