Study On Preparation And Properties Of Porous Carbon Based On Hemp By Strong Oxidant Activation Method

Biomass has been widely used in the synthesis of biomass porous because of its wide source,sustainability,recyclability.It has rich channel characteristics and excellent properties in supercapacitor energy storage.Pretreatment of carbon raw materials with chemical reagents(HNO3?H2O2?KOH?NaOH et al.)can optimize its morphology and structure,change the surface chemical functional groups and content,but its carbon mostly amorphous and with low degree of graphitization,low conductivity.However,strong oxidants can be used as pore formers and catalysts to complete graphitization and pore treatment,the strong oxidant activation method takes short time,simple,and environment friendly.It is a very excellent method of activation.The mesoporous carbon can be introduced into the framework of various structural carbon by the activation of strong oxidant.The larger specific surface area and wider pore size distribution make the prepared biomass porous carbon have excellent electrochemical performance.In addition,there have been few reports on the preparation of biomass porous carbon by the one-step carbonization activation method with strong oxidants.So we use KMnO4,KClO4,K2Cr2O7 as strong oxidants,by the one-step carbonization activation method to prepare the hemp-based porous carbon and to test.(1)The hemp raw material and the strong oxidant KMnO4 are evenly mixed in a certain proportion to obtain a dry mixture,and preparation of hemp-based porous activated carbon by different activation temperatures.Testing with SEM?HRTEM?N2 adsorption?XRD?XPS?Raman and FTIR.The activated carbon presents graded porous structure.The sample MMn-600 presents the best performance,its specific surface and pore volume is 1025m2/g,1.53cm3/g,its surface oxygen and nitrogen content is 12.33at%,1.26at%.In three electrode system of 6M KOH,the MMn-600 presents a high capacitance of 329F/g at a 0.1 A/g.In two electrode system of 6M KOH,it presents 280F/g at a 0.2A/g,with a little capacitance reduction of 6.25%after 10000 cycles at 5A/g,which indicating a good electrochemical stability.In two electrode system of 1MNa2SO4,it presents 147F/g at lA/g and 113F/g at 5A/g,and the pecific capacitance retention rate is 76.87%,it presents 14.75Wh/kg at a 425W/kg.It shows that it has excellent rate performance and high energy density.(2)The hemp material and the strong oxidant KClO4 are mixed to obtain a dry mixture,and preparation of hemp-based porous activated carbon by different temperatures.Testing with SEM?HRTEM?N2 adsorption?XRD?XPS?Raman and FTIR.The activated carbon presents graded porous structure.The sample MC1-500 presents the best performance,its specific surface and pore volume is 850m2/g,1.13cm3/g,its surface oxygen and nitrogen content is 12.5at%,1.36at%.In three electrode system of 6M KOH,the MC1-500 presents a high capacitance of 295F/g at a 0.1 A/g.In two electrode system of 6M KOH,it presents 248F/g at a 0.2A/g,with a little capacitance reduction of 8.51%after 10000 cycles at 5A/g,which indicating a good electrochemical stability.In two electrode system of 1M Na2SO4,it presents 135F/g at lA/g and 114F/g at 5A/g,and the pecific capacitance retention rate is 84.45%,it presents 11.98Wh/kg at a 399.33W/kg.It shows that it has excellent rate performance and high energy density.(3)The hemp material and the strong oxidant K2Cr2O7 are mixed to obtain a dry mixture,and preparation of hemp-based porous activated carbon by different temperatures.Testing with SEM?HRTEM?N2 adsorption?XRD?XPS?Raman and FTIR.The results show that the residual chromium oxide,the pore structure is not well distributed,the pore obstruction is not smooth,and the electrical performance is very poor.In three electrode system of 6M KOH,presents the highest capacitance of 149.4F/g at a 0.1 A/g,and 72.45F/g at 2A/g,presents poor capacitance performance and rate performance.