Enhancement of the Carbon Nanowall Film Capacitance. Electron Transfer Kinetics on Functionalized Surfaces

Abstract

The effects of electrochemical oxidation and surfactant adsorption on behavior of vertically oriented carbon-nanowall (CNW)-based electrodes are studied. Electrochemical oxidation is carried out by the electrode polarization in aqueous solutions at high anodic potentials corresponding to water electrolysis, whereas the modification of surface by surfactants is accomplished by the adsorption of molecules characterized by the cage-like structure. Using the methods of cyclic voltammetry and impedancemetry, it is shown that a substantial increase in the capacitance of CNW-based electrodes is observed in both cases (30-50-fold and 3-5-fold, respectively). The as-grown and modified electrodes are characterized by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. A substantial increase in a number of oxygen-containing functional groups is observed on the CNW surface after the electrode polarization at high anodic potentials. The kinetics of redox reactions on the CNW film surface is studied by comparing the behavior of systems [Ru(NH3)6](2+/3+), [Fe(CN)6](4-/3-), Fe(2+/3+), and VO3(-)/VO(2+). It is demonstrated that oxidation of nanowalls makes the electron transfer in the redox reaction VO3(-)/VO(2+) and the redox system Fe(2+/3+) considerably easier due to coordination of discharging ions of these systems with the functional groups; however, no such effect is observed for the redox-systems [Fe(CN)6](3-/4-) and [Ru(NH3)6](2+/3+).

Graphene Nanosheets Based Cathodes for Lithium-Oxygen Batteries

“…The observed higher capacitive current is due to the surface defects on the graphene. Such an analogous increase in capacitive current values is reported and it is stated that the surface defects lead to a significant increase in capacitance values and surface reaction kinetics in carbon nanomaterials [53,54]. In our work, a slightly higher capacitance is observed for Hybrid 1 in oxygen saturated KOH solution than in nitrogen saturated KOH, but the ratio of capacitance is reasonable.…”

Vertically Aligned Graphene Nanosheet Arrays: Synthesis, Properties and Applications in Electrochemical Energy Conversion and Storage

“…[131] Electrochemical oxidation of the VAGNAs surface was achieved by the electrode polarization in aqueous solutions at high anodic potentials, which could promote the electron transfer in the redox reaction VO 3 − / VO 2+ due to the coordination of discharging ions with the oxygenated functional groups. [132] To fabricate practicable and recyclable electrodes with reduced cost, VAGNAs were prepared on carbon felt by PECVD (Figure 10b-d). [133] Compared with the original carbon felt, the VAGNAs-decorated carbon-felt exhibited much decreased charge transfer resistance.…”

“…The morphology of VAGNAs was demonstrated to have strong influence on the battery performance in terms of lowering the overpotential, obtaining well‐shaped anodic and cathodic redox peaks with high peak densities, as well as achieving a long term stability, because the catalytic reaction between different oxidation states of vanadium (V 4+/5+ ) and electron transfer kinetics were closely associated with the conductivity of graphene nanosheets and the amount of exposed graphitic edge planes terminated with oxygenated functional groups ( Figure 10 a) . Electrochemical oxidation of the VAGNAs surface was achieved by the electrode polarization in aqueous solutions at high anodic potentials, which could promote the electron transfer in the redox reaction VO 3 − /VO 2+ due to the coordination of discharging ions with the oxygenated functional groups . To fabricate practicable and recyclable electrodes with reduced cost, VAGNAs were prepared on carbon felt by PECVD (Figure b–d) .…”

Recent Progress on Electrochemical Capacitors Based on Carbon Nanotubes

“…Figure 6 shows the effect of the addition of oxygen redox-active molecules on the electrochemical performance of CNTs. Nanotubular materials can be treated (CNTs-T) chemically [62][63][64][65][66][67][68][69][70], electrochemically [59,71,72], photochemically [73,74], and using plasma-induced techniques [75,76]. The chemical modifications are usually performed in concentrated nitric acid or in a mixture of nitric and sulfuric acids.…”