The Application Of Biomass Palm-shell-derived Porous Carbon In Electrochemical Energy Storage

Electrode materials are the main factor affecting the performance of supercapacitors and lithium-sulfur batteries.Due to the advantages such as relatively low cost,electrochemical stability and a wide range of working temperature,carbon materials are widely used in metallurgy,ceramics,catalysts,gas adsorbent and electrode materials.At present,porous carbon materials derived from the use of biomass instead of traditional mineral raw materials can not only optimize properties of materials,but also achieve a win-win effect of economic and environmental protection.So it has attracted more attention by researchers.In this paper,starting from the renewable biomass waste-palm kernel shell(PKS),as an inexpensive carbon source,we have purposefully proposed a simple and effective method to prepare PKS porous activated carbon through the initial carbonization and KOH chemical activation.The morphology,structure and properties of the as-prepared carbon materials were investigated by scanning electron microscopy(SEM),nitrogen adsorption method(BET),determination of iodine value and so on.Carbon electrodes were applied in supercapacitors and lithium-sulfur batteries.The major contents of this paper are as follows:(1)With a renewable biomass palm shell as a carbon source,the surface area of the palm kernel shells was 2760 m2 g-1 and the iodine adsorption value was up to 1100 m2 g-1,which was activated by initial carbonization and chemical activation with KOH as the activator.The effects of process parameters such as alkali-carbon ratio and activation temperature on the yield,specific surface area,pore volume,iodine adsorption value and microstructure of carbon were investigated.When the ratio of alkali to carbon was 4:1 and the activation temperature was 900 ?,the preparation process was best.The porous activated carbon of the PKS still belongs to amorphous carbon,which mainly contains C,H,O and a small amount of S,N elements.(2)The prepared PKS porous activated carbon was applied to supercapacitors.Palm kernel shells are a kind of low-cost carbon source,and its abundant cellulose,lignin and other ingredients also provide nitrogen,sulfur,phosphorus and other heteroatoms for the final product.The presence of heteroatoms not only provides the redox pseudostat,but also helps to suppress the irreversible changes in the oxygen-containing functional groups on the surface of carbon materials during the charging and discharging process.Benefit from the synergistic effect of the porous structure and its composition,the prepared PKS derived N,S,P co-doped activated carbon exhibits excellent electrochemical performance.In the case of 3.0 mol L-1 KOH electrolyte solution,the specific capacitance(CS)of the three-electrode system is 380 F g-1 at a current density of 1.0 A·g-1,and has good rate performance and cycle stability.In addition,the prepared symmetrical supercapacitor also has excellent cycling performance at 1.0 A g-1 current density and the maximum energy density can achieve 27.6 Wh kg-1 at a power density of 398.4 W kg-1.(3)The as-prepared activated carbon was developed as a conducting framework for lithium-sulfur battery cathode materials.The resulting activated carbon/sulfur composite cathode possesses a high specific capacity,good rate capability,and stable cycling performance.At 200 mA g-1 current density,the initial discharge capacity of the activated carbon/sulfur composite cathode with 60%sulfur content is 1045 mA h g-1.At a current density of 800 mA g-1,the activated carbon/sulfur composite cathode shows 66%capacity retention over 1000 cycles with the coulombic efficiency remaining at approximately 99%.The good electrochemical performance can be attributed to the excellent structural parameters of the activated carbon.The ultrahigh specific surface area and large pore volume not only enhances the sulfur content but also ensures dispersion of elemental sulfur in the conducting framework,thereby improving sulfur utilization.The small pores of the activated carbon can effectively inhibit the diffusion of polysulfides during the charge/discharge process.