No abstract

No abstract

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.

Carbon nanotubes (CNTs) have been applied as catalysts in the VO/VO redox, whereas the mechanism of CNTs for the redox reaction is still unclear. In this work, the mechanism of the VO/VO redox is investigated by comparing the electrocatalytic performance of CNTs with different distributions. For different CNTs, the peak current density of the VO/VO 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 VO/VO 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 to 45.4 mA mg whilst the peak potential separation (ΔE) 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 VO/VO redox.

Graphene has extensive application in various prospects due to its good stability, high conductivity, and large specific surface area. However, the dispersion of graphene in solvents can significantly affect the preparation of graphene-supported metal nanoparticles through wet chemistry methods. In this work, a density functional theory calculation is carried out to study the interaction between graphene and various solvent molecules. According to the calculation, there is a correlation between the interaction energy (E a ) and the dispersion concentration of graphene in different solvents. In addition, we use methanol, ethanol, or 2-propanol as solvents to prepare graphene-supported palladium nanoparticles. The size of the nanoparticles decreased with stronger interaction between graphene and solvent molecules when using methanol, ethanol, or 2-propanol as solvents. Furthermore, there is a good correlation with the size of the nanoparticles and interaction energies between graphene and solvent molecules, which confirmed that E a is an effective descriptor for graphene dispersion in solvents. This work provides insightful information to understand the dispersion mechanism of graphene in solvents and preparation of graphene-supported metal nanoparticles through wet chemistry methods.