No abstract

No abstract

No abstract

FIB-SEM, XPS, TOF-SIMS and electrochemical methods have been used for the characterization of physical properties and chemical composition of microporous carbide derived carbon electrodes, prepared from TiC at 950 • C (noted as TiC-CDC) after 40000 charge/discharge cycles. Changes in surface chemical composition of TiC-CDC electrodes, includes partial contamination with reaction intermediates (F 2 , CH − , CHO − , CN − , organic radicals), and Al current collectors, like partial dissolution of Al from positively charged electrode and deposition of Al onto the negatively charged TiC-CDC electrode surface, have been analyzed. The values of gravimetric energy (taking into consideration the active TiC-CDC material weight only) calculated before and after constant current charge/discharge cycling at cell voltage 3.4 V are quite similar (35 and 34 W h kg −1 , respectively). At starting moment the gravimetric power was practically 1.4 times higher (195 kW kg −1 , 146 kW dm −3 ) than that calculated after 40000 charge/discharge cycles (144 kW kg −1 , 104 kW dm −3 ). The characteristic relaxation time constant (0.94 and 1.23 s, respectively) increases somewhat in accordance with the decrease of power density during long-lasting cycling at higher cell voltage range from 0.2 to 3.4 V.

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.