3-D Graphene Derived-from Biomass And Application In Supercapacitor

As a kind of quasi two-dimensional material,graphene has many excellent properties and has broad application prospects in the field of electrochemical energy storage and conversion.While there are some shortcomings about traditional synthetic methods of graphene,for example:complex process,serious environmental pollution and high cost,so it has been a major issue to seek a new way to prepare graphene with simple operation and pollution free.Supercapacitor had more and more application in electronic and electric vehicles as a new generation energy storage system.Based on these,the work presented a new simple and clean method to prepare 3D graphene with coconut shell or other biomass as carbon source,and studied the electrochemical performance of as-prepared 3D graphene used in supercapacitor.3DPG was synthesized through a straightforward process which named"carbonization-activation combination method" using biomass waste(coconut)as raw material.The experiment obtained the optimal technological parameters as following:The coconut shell powder was pre-carbonized at 350℃ for 1 h,then thermal treatment at high temperature for 2 hour and gained the carbonized material,at the weight ratio of 6:1 between activation agent(K2CO3)and carbonized material,the composite was activated at 900℃ for 60min.The as-prepared 3DPG had an interconnected 3D network that composed of crumpled graphene sheets;meanwhile,it had abundant micropore and specific surface up to 940 m2 g-1.What’s more,it also obtained 3DPG when the raw material was replaced by walnut,almond,pistachio,hazel.The result showed the new way was suited for other biomass to prepared 3D graphene.The electrochemical performance of as-prepared 3DPG was studied by assembling it into supercapacitor with two-electrode system.The electrochemical tests showed that 3DPG revealed good behavior of electrical double layer capacitor and had a specific capacitance of 132 F g-1,per square capacitance up to 14.0 μF cm-2.A high capacitance retention ratio(91.7%)after 1000 cycles suggested the as-prepared 3DPG had a good cycle performance,and galvanostatic charge/discharge test at various current densities showed it obtained excellent rate performance.3DPG with high specific surface(HS-3DPG)was synthesized according to these technological parameters:the coconut shell powder was firstly carbonized at 400℃for 1 h and then high temperature treatment for 2 h,the carbonized material was achieved.Secondly,the carbonized material and activation agent was activated at 800℃for 2 h with a weight ratio of 3:3:lamong KOH,K2CO3 and carbonized material.As a result,the as-prepared HS-3DPG obtained specific surface of 1350 m2 g-1.The electrochemical tests showed that 3 DPG revealed good behavior of electrical double layer capacitor and displayed a specific capacitance of 156 F g-1 at a current density of 1 A g-1 and galvanostatic charge/discharge test at various current densities showed it obtained excellent rate performance.HS-3DPG with different pore structures were prepared and used in supercapacitor by changing the weight ratio of activation agent and carbonized material The results showed that pore volume and pore size increased while the specific surface decreased with the continuous increasing of activation agent.The specific capacitance increased along with specific surface and the ratio of mesoporous,it indicated large specific surface was favorable for absorption of electrolyte ions and mesoporous provided abundant path for transport of electrolyte ions.Among these samples,the best sample displayed a specific capacitance of 273.2 F g-1 and capacitance retention 240.4 F g-1 after 1000 cycles.