Supercapacitor electrodes from activation of binderless green monoliths of biomass self-adhesive carbon grains composed of varying amount of graphene additive

Binderless electrodes of activated carbon monoliths (ACMs) and its composites with graphene are prepared by carbonization and activation of green monoliths consisting of self-adhesive carbon grains and 0-10 wt% KOH-treated graphene. Compared with ACMs, the optimized composite containing 6 wt% graphene exhibits more ordered micro-structures with increased crystallite height, and graphitic sp(2) carbons (I (D) /I (G) = 0.49 vs. 0.91) along with enhanced porosity; as revealed by X-ray diffraction, Raman, and N-2 adsorption-desorption studies. These modifications lead to increased electrical conductivity (13 vs. 9 S cm(-1)) through improved interconnections of carbon particles by graphene, and surface area similar to (800 vs. 456 m(2) g(-1)) due to increased inter-particle spacing. Further, contrary to ACMs, the composite electrodes can offer faster delivery of energy in almost 50% less response time (5 vs. 8 s) due to reduced equivalent series resistance (1.67 vs. 2.65 Omega) and charge transfer resistance (0.55 vs. 1.33 Omega).