Tuning the structure of in-situ synthesized few layer graphene/carbon composites into nanoporous vertically aligned graphene electrodes with high volumetric capacitance

Abstract

Few layer graphene/carbon (FLG/C) composites are prepared directly via the rapid and simple exfoliation of expanded graphite in the presence of carbon based natural precursors (i.e. protein, polysaccharide) in water, followed by carbonization process. Several parameters such as nature of C-precursor, FLG/C ratio and carbonization conditions (gas, temperature) are modified in order to optimize the morphology, composition and porosity of FLG/C and thereby investigate their impact on gravimetric and volumetric capacitance, their stability and contribution of pseudocapacitance (Ps) vs. Double-layer capacitance (DL). Few composites exhibit extremely high capacitance considering their low BET-surface area ranging in 130–260 m2/g. The highest gravimetric and volumetric capacitance of 322 F/g and 467 F/cm3 respectively (0.5 A/g); and energy/power performance is reached for FLG/C:1/2, synthesized from graphite-bovine serum albumin (BSA). Despite relatively high theoretical pseudocapacitance contribution of 69% (1.1 V), this sample shows also high capacity retention at high current density and elevated energy -to- power densities. The overall great capacity performance is attributed to the high electrochemical surface area from combined structural features: ultramicroporosity, FLG alignment with high accessibility of FLG edges and elevated packing density. The transport limitation enhances however at higher scan rate (>100 mV/s).