Performance of carbon xerogel-graphene hybrids as electrodes in aqueous supercapacitors

A pristine carbon xerogel (AX) and two hybrid samples (AX-3% and AX-9%), with different graphene percentages (3 and 9 wt%), were synthesized using a fast and economical process. It was observed that graphene produces less shrinkage of the xerogel structure during synthesis. Moreover, the electrical conductivity of the materials increases linearly with the percentage of graphene added. Thus, AX-9% presents an electrical conductivity 135 and 321% greater than that of AX-3% and AX, respectively. As a result of the good pore size distribution and high electrical conductivity of AX-9%, when this material is used as electrode in supercapacitors, the resistance of the cell is reduced; therefore, better power densities are obtained. However, its capacitance values are the same as those of AX-3%. The performances of these materials as electrodes in supercapacitors were evaluated taking into account the influence of their porosity and electrical conductivity. Moreover, AX and AX-9% were subjected to mild oxidation with air to study the effect of air on the porosity, electrical conductivity, and performance of these treated samples as electrodes in supercapacitors.