Single-Entity “Nano-Catalysis”: Carbon Nanotubes and the VO₂⁺/VO²⁺Redox Reaction

Abstract

Cyclic voltammetry and single-entity electrochemistry (aka "nano-impacts") are used to evaluate the electrocatalysis of the VO 2 + /VO 2+ redox couple by means of bamboo-like multiwalled carbon nanotubes particularly in comparison with the kinetics seen at carbon macro-electrodes. The individual nanotubes are shown to accelerate the reaction in the oxidative direction but to retard it in the reductive direction! The asymmetry is explained in terms of the multistep nature of the electrode reaction and the relative sequence of electron transfer and chemical steps. When an ensemble of nanotubes is drop-casted onto a glassy carbon electrode, an electrochemically nearly reversible response is seen and understood in terms of the changed mass transport regime under which the reaction occurs.

Voltammetry of Carbon Nanotubes and the Limitations of Particle-Modified Electrodes: Are Carbon Nanotubes Electrocatalytic?

“…The plots of current versus potential shown correspond to the quasi-steady-state voltammograms for the two electrode processes at single CNTs and, with a knowledge of the relevant formal potential for the bromine/bromide couple, can be analyzed to give a quantitative assessment of the extent of electrocatalysis. Similar comparative observations were made with respect to the VO 2 + /VO 2+ couple except that the multistep reaction involving bond breaking/making and proton transfer steps in combination with electron transfer was shown to be catalyzed by CNTs in the oxidative direction but retarded in the reductive direction! The single-entity approach has also been used to reveal the role of surface oxygen functionality, such as, and especially quinones, in the reduction of oxygen in aqueous base. , We note that beyond electrocatalysis the electro-oxidation of the CNTs themselves either undoped or with amino functionalization has been characterized …”

“…Similar comparative observations were made with respect to the VO 2 + /VO 2+ couple except that the multistep reaction involving bond breaking/making and proton transfer steps in combination with electron transfer was shown to be catalyzed by CNTs in the oxidative direction but retarded in the reductive direction! 50 The single-entity approach has also been used to reveal the role of surface oxygen functionality, such as, and especially quinones, in the reduction of oxygen in aqueous base. 51,52 We note that beyond electrocatalysis the electrooxidation of the CNTs themselves either undoped or with amino functionalization has been characterized.…”

Understanding Carbon Nanotube Voltammetry: Distinguishing Adsorptive and Thin Layer Effects via “Single-Entity” Electrochemistry

“…These were assigned to capacitive impacts consistent with the increase in capacitive currents at high positive potentials 33,34 and also the oxidation of the b-MWCNTs themselves as discussed elsewhere. 35 The impact signals seen in the absence of HR are tiny in comparison with the Faradaic signals seen in the presence of HR; hence, attention was next turned to the further consideration of these signals.…”

Multiple‐dimensioned defect engineering for graphite felt electrode of vanadium redox flow battery

“…However, graphite felt undergoes graphitization treatment of ultrahigh temperature, which results in its poor wettability and inadequate active sites for vanadium redox reactions 15 . To resolve this problem, many modification methods have been proposed to enhance the electrochemical catalysis of graphite felt via increasing surface area and introducing heteroatom, functional group, and catalyst 16–21 . Among these methods, the introduction of heteroatom and functional group is superior to the introduction of catalyst in terms of electrode's stability during long‐time operation because the catalyst deposited on the electrode is easy to fall off under the impact of flowing electrolyte.…”