The Effect of Functional Groups on the Electrocatalytic Activity of Carbon Nanotubes with Different Wall Numbers toward Carbohydrazide Oxidation Reaction.

Carbohydrazide could be applied as fuels for fuel cells to avoid the toxicity of hydrazine. Carbon nanotubes (CNTs) exhibit an improved electrocatalytic activity toward carbohydrazide oxidation reaction than other carbon materials like carbon black or multi-layer graphene, however, the role of defects and functional groups of CNTs for the reaction is not clear. In this study, the electrocatalytic properties of CNTs toward the carbohydrazide oxidation reaction is investigated, which demonstrate that the content of carboxyl groups is crucial to the catalytic activity. The one with higher carboxyl groups exhibits an improved catalytic activity toward carbohydrazide oxidation reaction. Furthermore, density functional theory calculation reveals that the carboxyl groups could increase the adsorption of carbohydrazide molecules on CNTs, which benefits their catalytic activity.

The electrocatalytic characterization and mechanism of carbon nanotubes with different numbers of walls for the VO2+/VO2+ redox couple.

Carbon nanotubes (CNTs) have been applied as catalysts in the VO2+/VO2+ redox, whereas the mechanism of CNTs for the redox reaction is still unclear. In this work, the mechanism of the VO2+/VO2+ redox is investigated by comparing the electrocatalytic performance of CNTs with different distributions. For different CNTs, the peak current density of the VO2+/VO2+ redox increases with increasing content of oxygen-functional groups on the surface of CNTs, especially the carboxyl group which is proved as active sites for the redox reaction. Moreover, the reversibility of the VO2+/VO2+ redox decreases with increasing defects of CNTs, as the defects affect the charge transfer of the catalytic reaction. Nevertheless, when a multi-walled CNT sample is oxidized to achieve a high content of oxygen functional groups and defects, the peak current density of the redox reaction increases from 38.5 mA mg-1 to 45.4 mA mg-1 whilst the peak potential separation (ΔEp) also increases from 0.176 V to 0.209 V. Overall, a balance between the oxygen functional groups and the defects of CNTs affects the peak current and the reversibility for the VO2+/VO2+ redox.