A Hybrid Capacitor Based on Fe₃O₄-Graphene Nanocomposite/Few-Layer Graphene in Different Aqueous Electrolytes

Graphene nanoplatelets have been used for synthesis of Fe 3 O 4 -graphene nanocomposite negative electrode. A high-resolution transmission electron microscopy measurements of the graphene areas surrounded by Fe 3 O 4 nanoparticles show that the graphene has folded on itself and the edges have some amounts of waviness which could indicate existence of amorphous carbon. A high energy density hybrid capacitors (HC) have been completed based on 1 M Li 2 SO 4 , Na 2 SO 4 , Rb 2 SO 4 , Cs 2 SO 4 and MgSO 4 aqueous electrolytes and Fe 3 O 4 -graphene nanocomposite/few-layer graphene electrode materials. The optimal working potential region of each electrode has been regulated by optimized mass balance of the electrodes. After optimization the cell voltage increased up to 1.4 V and an energy density (maximal) up to 9.4 Wh kg −1 in 1 M Cs 2 SO 4 electrolyte. The maximal power density 41.1 kW kg −1 has been calculated for 1 M Rb 2 SO 4 aqueous electrolyte based HC. The energy and power density of completed HC cells decreased with solvation Gibbs energy of the cations. The cycling efficiency values have been calculated being highest for 1 M Rb 2 SO 4 and 1 M Cs 2 SO 4 electrolyte based systems, 98.4% and 99.9%, respectively. Thus, promising HC cells based on Fe 3 O 4 -graphene nanocomposite/few-layer graphene electrodes in different aqueous electrolytes have been developed and characterized.