Research On Application Of Rice Husk-based Porous Carbon Materials In Electrochemical Energy Storage

Rice husk-based porous carbon?RHPC?,derived from biomass waste of rice husk,is a kind of amorphous carbon material.It usually exhibits low graphitization degree,nearly amorphous morphology and periodic structure.The same as other amorphous carbon materials,there are still disordered,irregular and tiny graphite crystals and defects in the internal structure of RHPC.Studies demonstrated RHPC shows excellent physical and chemical properties due to its porous structure and large specific surface area,enabling the widely use of RHPC in the fields of gas absorption,ion and organic species absorption and supercapacitors,etc.Along with the growing maturity of RHPC preparation technology and the increasing industrial demand,there is a great necessity nowadays to expand the application scope of RHPC,improving its application value and promoting its industrialization development.In view of the current research status and industrial background of RHPC,we explore herein the synthesis and application of RHPC in the field of electrochemical energy storage based on the in-depth understanding of structural characteristics and physicochemical properties of RHPCs.The main results are listed as follows:?1?We studied the use of RHPC as an additive in positive electrodes of lead acid batteries in which its role in positive electrodes was discussed.Results indicate the addition of RHPC increases the content of 3BS that is in decreased crystallinity and smaller particle size in cured electrode.In addition,it improves the formation efficiency,and the electric conductivity and electron transfer rate of positive electrode are also enhanced.Under 100%deep of discharge,the discharge capacity of RHPC electrode increased by 16%at 0.05C and 23%at 1C compared to that of blank electrode.Besides,the RHPC experimental cell keeps higher discharge specific capacity compared to the blank experimental cell in a long-term deeply charge/discharge process.The rich pore structure in RHPC is beneficial to the improvement of the mass transfer in such a typical thick electrode,thus reducing effectively the risk of the failure due to the mass transfer limit.The particle growth rate of positive active materials will be inhibited during long-term deeply charge/discharge,thus the addition of RHPC is beneficial to increasing the cyclic life of the positive electrode.?2?Typically,C/Sn O₂ composite with porous carbon as the carrier is prepared to stabilize Sn O₂ anodes in lithium-ion batteries.However,the application of present porous carbon materials is inhibited by high cost and complex preparation procedures.In this chapter,a new C/Sn O₂ composite was fabricated using the low-cost and easily available rice-husk based porous carbon.The cheap RHPC material can be easily obtained by convenient carbonization and activation of rice husk.Subsequently,a RHPC/Sn O₂ composite was prepared via a simple melt-impregnation method followed by heat treatment.The HRTEM image indicates that the RHPC possesses abundant meso-and micro-pore structures.The Sn O₂nanoparticles can be loaded on the RHPC matrix with average particle size of ca.5nm.The cyclic measurements showed that fifty discharge capacity of RHPC/Sn O₂anode at the current density of 100 m A g^-1 was 550 m Ah g^-1.Results indicate that the cyclic performance of RHPC/Sn O₂ anode is remarkably enhanced compared to the Sn O₂ anodes(180 m Ah g^-1 for Sn O₂ anode)due to the introduction of RHPC matrix.Moreover,the advance of low cost and easy preparation shown by RHPC and the improved stability of the composite anode suggest RHPC/Sn O₂is promising anode material in lithium-ion batteries.?3?A high-performance RHPC-based electrocatalyst for oxygen reduction reaction?ORR?was prepared by ammonia treatment at high temperature.The as-prepared N-RHPC electrocatalyst has the same ORR activity as the commercial Pt/C catalyst in alkaline solution.In addition,the as-prepared N-RHPC electrocatalyst also showed excellent long-term stability and methanol tolerance.The enhancement of electrocatalytic activity can be rooted in the increase of mesoporous volume by ammonia at high temperature,which provides more channels for ion transport,and the improvement of the graphitization degree and effective modification by N atoms,thus obtaining a large number of catalytic sites.We also studied a method of preparing high-performance RHPC-based electrocatalyst?N/RHPC?for ORR by confining pyrolysis of melamine in the micropores of RHPC.The activity and long-term performance of the as-prepared N/RHPC catalyst was similar to that of the commercial Pt/C catalyst.The enhancement of electrocatalytic activity can be attributed to the pretreatment of RHPC and melamine in aqueous solution by heating,stirring and evaporation.This operation makes melamine confined in the micropores of RHPC,leading a higher N atoms utilization rate after pyrolysis.