Fabrication and characterization of high performance carbon/metal-oxide nanocomposite supercapacitors

Depletion of fossil fuel resources due to rapid increase in energy demand has become a worldwide concern, and requires development of sustainable and eco-friendly energy storage and conversion systems for efficient utilization of alternative energy sources. Supercapacitors with high power and energy densities and long cycle lives offer best solutions for deposition of huge and fluctuating amounts of energy generated by alternative energy sources. Supercapacitors can store energy either by non-faradaic charge separation (electrical double layer capacitors, EDLCs) or by faradaic surface redox reactions (pseudocapacitors). Conventionally porous, high specific surface area (1000-2000 m2 g-1) activated carbons are used in EDLCs, and redox active transition metal oxides are used in pseudocapacitors. Ruthenium oxide (RuO2) is widely studied as electrode material; however, its toxicity, high cost, and scarcity necessitate seeking alternative pseudo-capacitive materials. Hybrid supercapacitors, comprising carbon/metal-oxide nanocomposites as electrode materials, benefit from high power density (charge-discharge rate) of porous carbon and high energy density of metal oxide, simultaneously. In this work, hazelnut shells (biomass) were used as a carbon source. Fe3O4 nanoparticles were produced by chemical co-precipitation method. In order to obtain porous Fe3O4/C nanocomposite, Fe3O4 nanoparticles were incorporated into biomass by realizing hydrothermal carbonization and MgO templating simultaneously in one pot. After physical characterizations, electrochemical performances of the Fe3O4/C electrode were investigated with a three-electrode cell in 1M Na2SO4 aqueous solution with and without adding different concentrations of Triton X-100 surfactant by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) tests. The best specific capacitance was obtained with 0.0025M surfactant added 1M Na2SO4 solution (161 F g-1 at 1 A g-1, ∆V=1.2 V). A symmetric supercapacitor was also produced reaching maximum energy density of 4 Wh kg-1 (∆V=1.8 V).