Molecular configurations of the 1.0 mol dm ⁻³ and 8.0 mol dm ⁻³ NaClO ₄ aqueous electrolytes, and shear viscosity and ionic conductivity as a function of the molar and molal concentrations of NaClO ₄ aqueous solutions.

We report here density functional theory calculations and molecular dynamics atomistic simulations to determine the total capacitance of graphene-modified supercapacitors. The contributions of quantum capacitance to the total capacitance for boron-, sulfur-, and fluorine-doped graphene electrodes, as well as vacancy-modified electrodes, were examined. All the doped electrodes presented significant variations in quantum capacitance (ranging from 0 to ∼200 μF cm⁻²) due to changes in the electronic structure of pristine graphene. The graphene-modified supercapacitors show any appreciable effect on double-layer capacitance being virtually the same for all the devices investigated. The total differential capacitance was found to be limited by the quantum capacitance, and for all the systems, it is lower than the quantum capacitance over the entire voltage window. We found that the total capacitance can be optimized by considering an adequate modification to each electrode in the supercapacitor. In addition, we found that an asymmetric supercapacitor assembled with different doped electrodes, i.e. an F doped negative electrode and an N doped positive electrode, is the best choice for a supercapacitor since this combination results in better capacitance over the entire potential window.

A double-channel transmission line impedance model was applied to the study of supercapacitors to investigate the charge transport characteristics in the ionic and electronic conductors forming the electrode/solution interface. The macro homogeneous description of two closely mixed phases (Paasch–Micka–Gersdorf model) was applied to study the influence of disordered materials on the charge transport anomalies during the interfacial charge–discharge process. Different ex situ techniques were used to characterize the electrode materials used in electrical double-layer (EDLC) and pseudocapacitor (PC) devices. Two time constants in the impedance model were adequate to represent the charge transport in the different phases. The interfacial impedance considering frequency dispersion and blocked charge transfer conditions adequately described the charge storage at the interface. Deviations from the normal (Fickian) transport involving the ionic and electronic charge carriers were identified by the dispersive parameters (e.g., n and s exponents) used in the impedance model. The ionic and electronic transports were affected when the carbon-based electrical double-layer capacitor was converted into a composite with strong pseudocapacitive characteristics after the decoration process using NiO. The overall capacitance increased from 2.62 F g⁻¹ to 536 F g⁻¹ after the decoration. For the first time, the charge transport anomalies were unequivocally identified in porous materials used in supercapacitors with the impedance technique.

A green chemical method is reported for the synthesis and functionalisation of high surface area carbon-based materials for applications as electrodes in short-term energy storage devices, such as supercapacitors. The proposed method is focused on sustainable chemistry and engineering and our results evidence excellent performance of electrochemical capacitor devices with high cycle life over a wide working voltage with low equivalent series resistance (ESR). Great enhancement of electrode wettability and charge transfer at the electrode/electrolyte interfaces using oxygenated surface functional groups were obtained using the present method. Actually, the present findings are quite promising thus encouraging further investigations of this green-functionalisation method for all other carbon materials, such as graphene, carbon nanotubes, doped-diamond, and so on.