Kachmar A. Charge storagemechanisms of electrochemical systems based on metal oxides or sulfides and carbonnanocomposite materials.

The conducted experimental investigations and theoretical calculations made it possible to establish the nature and general patterns of charge accumulation in electrochemical systems that are formed on the basis of Mo2O, MoS2 and MoO2/rGO, MoO2/Carbon, MoS2/rGO, MoS2/Carbon nanocomposite materials. Functioning of these electrochemical systems is associated with the presence of electric double layer and reversible faradaic processes. Transport processes in these structures have been investigated.Optimal conditions for obtaining and modifying activated carbon material doped with nitrogen-containing groups have been established. Under these conditions the material was characterized byhigh values of specific capacitance, specific surface area and electrical conductivity when used as a material for the creation of electrochemical energy storage systems. It has been found that the only mechanism of charge accumulation for capacitors based on alkaline-activated materials is the recharge processes of the electric double layer without the participation of redox reactions.It has been investigated that pore volume increases and the formation of NO2 nitrogen groups on the surface of carbon particles is observed due to the double thermochemical activation of the porous carbon material with the participation of the NaOH activating agent and HNO3doping of the carbon matrix.The crystalline structure, morphology and electrical properties of molybdenum oxide and sulfide and complexes on the basis of molybdenum oxide/sulfide and carbon/graphene oxide have been described. The materials weresynthe-sized by low-temperature hydrothermal method at different mass ratio of precursors. It has been found that the specific electrical conductivity values of composite materials are an order of magnitude higher than that of pure MoO2. This allows the efficient use of the redox component of MoO2 specific capacit-ance in the creation of hybrid electrochemical systems. The specific capacitance value of MoO2/rGO (1:2) composite materials was calculated according to the data of the galvanostatic cycle at a current density value of 1 A/g and reached 395 F/g. The specific capacitance value for this material from cyclic voltam-mogram data is 232 F/g at a scan rate value of 0.5 mV/s. Similar data were observed for MoO2/Carbon composite material with components` mass ratio of 1:1. After careful study of the data obtained for elec-trochemical systems on the basis of the obtained composite materials in the electrolytic medium the scheme of possible mechanisms of redox reactions on the materials of MoO2/rGO and MoO2/Carbon electrodes was proposed. Diffusion coefficient values of 1.3•10-12 and 4.1•10-12 cm2/s were calculated for MoO2/rGO materials with 1:1 and 1:2 ratios, respectively.When analyzing the galvanostatic and potentiodynamic cycling data for the materials of the MoS2, MoS2/rGO and MoS2/Carbon systems, themaximum discharge capacitance is observed for the case of MoS2/Carbon composite material (about 190 F/g forgalvanostatic data and about 200 F/g forpotentiodynamic cycling). Moreover, this material was characterized by the relatively slowest rate of the capacitance decrease with discharge current increasing or scan rate increasing.