No abstract

Single-entity electrochemistry measurements were used to compare the electrocatalysis of the oxygen reduction reaction (ORR) by means of multiwalled carbon nanotubes (MWCNTs) or amino-functionalized multiwalled carbon nanotubes (MWCNTs-NH2). All of the evidence showed that an electroactive surface oxygen functionality played the most important role in the catalysis process, not the nitrogen content.

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.

The morphology of electrodes modified by drop casting layers of multi‐walled carbon nanotubes (MWCNTs) and platinum nanoparticles (PtNPs) is investigated and shown to exhibit significant heterogeneity, both in the form of ‘patchy’ surfaces and of ‘coffee rings’ formed after evaporation of the carrier solvent. The variation of the heterogeneity with total average coverage is studied and the consequences for quantitative analytical voltammetry assessed. Specifically, the oxidation of bromide in aqueous solution is examined in the case of MWCNTs‐modified electrodes and the oxidation of aqueous As(III) in that of PtNPs‐modified electrodes. In both cases, significant deviations from the expected voltammetry are observed, even for average coverages that correspond to much in excess of a monolayer of CNTs or NPs. The observed voltammetry is related to the observed structure and the use of such modified electrodes, without concomitant microscopic surface characterization, is caveated.

We explore via simulation, the cyclic voltammetry of the following mechanism involving a reversible electrode process coupled with a follow up reaction in which the product (𝐵) of the electrode reaction reacts chemically with the reactant, 𝐴, to form a species 𝐶:Such a mechanism is shown, under certain critical combinations of rate constant and reactant concentration to give rise to two voltammetric peaks despite the assumption of a single redox couple (𝐴/𝐵). This results from the formation of 𝐶 during the first peak whilst the second peak, seen at more oxidizing potentials, reflects the dissociation of 𝐶 releasing 𝐴. A mechanism of the type investigated may hold during the oxidation of bromide(𝐵𝑟 − , 𝐴) in solution to form bromine(𝐵𝑟 2 , 𝐵) and tribromide (𝐵𝑟 3 − ,𝐶).Simulations are used to explore the conditions for which two peaks are expected in the bromide oxidation system in aqueous solution and for which the two following limiting cases operate