Insights into the Conductive Network of Electrochemical Exfoliation with Graphite Powder as Starting Raw Material for Graphene Production.

Electrochemical exfoliation starting with graphite powder as the raw material for graphene production shows superiority in cost effectiveness over the popular bulk graphite. However, the crucial conductive network inside the graphite powder electrode along with its formation and influence mechanisms remains blank. Here, an adjustable-pressure graphite powder electrode with a sandwich structure was designed for this. Appropriate encapsulation pressure is necessary and conducive to constructing a continuous and stable conductive network, but overloaded encapsulation pressure is detrimental to the exfoliation and graphene quality. With an initial encapsulation pressure (IEP) of 4 kPa, the graphite powders expand rapidly to a final stable expansion pressure of 49 kPa with a final graphene yield of 46.3%, where 84% of the graphene sheets are less than 4 layers with ID/IG values between 0.22 and 1.24. Increasing the IEP to 52 kPa, the expansion pressure increases to 73 kPa, but the graphene yield decreases to 39.3% with a worse graphene quality including higher layers and ID/IG values of 1.68-2.13. In addition, small-size graphite powders are not suitable for the electrochemical exfoliation. With the particle size decreasing from 50 to 325 mesh, the graphene yield decreases almost linearly from 46.3% to 5.5%. Conductive network and electrolyte migration synergize and constrain each other, codetermining the electrochemical exfoliation. Within an encapsulated structure, the electrochemical exfoliation of the graphite powder electrode proceeds from the outside to the inside. The insights revealed here will provide direction for further development of electrochemical exfoliation of graphite powder to produce graphene.

Nickel Acetate-Assisted Graphitization of Porous Activated Carbon at Low Temperature for Supercapacitors With High Performances.

Catalytic graphitization opens a route to prepare graphitic carbon under fairly mild conditions. Biomass has been identified as a potentially attractive precursor for graphitic carbon materials. In this work, corn starch was used as carbon source to prepare hollow graphitic carbon microspheres by pyrolysis after mixing impregnation with nitrate salts, and the surface of these carbon microspheres is covered with controllable pores structure. Under optimal synthesis conditions, the prepared carbon microspheres show a uniform pore size distribution and high degree of graphitization. When tested as electrode materials for supercapacitor with organic electrolyte, the electrode exhibited a superior specific capacitance of 144.8 F g-1 at a current density of 0.1 A g-1, as well as large power density and a capacitance retention rate of 93.5% after 1,000 cycles in galvanostatic charge/discharge test at 1.0 A g-1. The synthesis extends use of the renewable nature resources and sheds light on developing new routes to design graphitic carbon microspheres.