Reduced graphene oxide-modified biochar electrodes via electrophoretic deposition with high rate capability for supercapacitors

Wood-derived biochar is an attractive material for supercapcitor electrodes due to its natural hierarchical structure. To improve the conductivity of biochar, graphene oxide is electrophoretically deposited, followed by electrochemical reduction. The conductivity can be controlled by either changing the amount of reduced graphene oxide loading by using different concentrations of graphene oxide suspension or by reaching different reduction states by varying the electrochemical reduction potential. The pore structure is also investigated to evaluate the microstructure effect on the material's capacitive behavior. A specific capacitance of 167 F g(-1) is achieved after reduced graphene oxide deposition, which is 4.3 times higher than that of biochar without reduced graphene oxide. The reduced graphene oxide-modified biochar electrodes show a high rate capability retention of approximately 90% with current densities from 0.5 to 3.0 A g(-1). Additionally, no degradation is observed after 10,000 charging-recharging cycles under 5.0 A g(-1). Graphic abstract As the conductivity of raw biochar is low, it has been modified by reduced graphene oxide through electrophoretic deposition and electrochemical reduction. As a result, the conductivity increases approximately 4 times, but the surface area and pore volume decrease because of pore blockage by graphene. Finally, the reduced graphene oxide-modified biochar electrode exhibits specific capacitance 4.3 times higher than that of raw biochar. The rate capability has also been improved due to the enhanced electron transportation.