Reduced graphene oxide hydrogels prepared in the presence of phenol for high-performance electrochemical capacitors

Reduced graphene oxide (GO) hydrogels were synthesized by the hydrothermal treatment of GO in the presence of phenol to obtain rGOHPhs, where phenol acted as both a reducing agent and a structure regulator for the hydrogels. The influence of the mass ratio of GO to phenol and the hydrothermal temperature on the capacitive behavior of the rGOHPhs were investigated. Results indicate that the rGOHPhs have a more developed three-dimensional pore network than the rGOH samples without phenol under the same hydrothermal conditions. The optimum rGOHPh was prepared at 160 °C for 12 h with a GO/phenol mass ratio of 1/ 1.25 and had a larger micropore and total pore volume than rGOH prepared under the same hydrothermal conditions. The optimum rGOHPh had a specific capacitance of about 260.0 F g-1 at a scan rate of 1 mV s-1, which is much higher than that of the rGOH (182.5 F g-1). Furthermore, the optimum rGOHPh has an excellent rate capability (138.1 F g-1 at 500 mV s-1) and a good cycling stability (98.3% capacitance retention after 12 000 cycles). A capacitor assembled using the optimum rGOHPh had energy densities of about 8.9 and 2.0 Wh Kg-1 at power densities of 0.125 and 16 kW kg-1, respectively, which are higher than most of the GO-based capacitors reported in the literature. The well-developed pore network is ascribed to the phenol and its oxidation product quinone that were adsorbed on the rGO surface as spacers and redox pairs to provide pseudo capacitance.