Electrochemical study of H3PMo12 retention on Vulcan carbon grafted with NH2 and OH groups

Abstract

In this work, we show a comparative study based on the effects of specific chemical functional groups (-OH, -NH 2 ), grafted on Vulcan carbon (VC) with the incorporation of a specific polyoxometalate (POM), PMo 12 (H 3 PMo 12 O 40 ), to improve electrochemical performance. We observed a decrease in the specific surface area of the grafted matrices (VC-OH and VC-NH 2 ) [1], and the same trend was observed for PMo 12 (POM) incorporation. Our electrochemical studies showed low concentrations of POM in unmodified VCs and higher POM concentrations for grafted matrices (VC-OH and VC-NH 2 ) after 500 voltammetric cycles, especially for the VC grafted with -OH groups (VC-OH-POM). Mechanisms have been proposed for POM interaction with the grafted groups in carbon, emphasizing the role of aqueous medium and redox activity of POM. Cyclic voltammograms suggested the POM anchoring through -OH groups with a strong interaction as a covalent bond, resulting in a surface coverage of 1.66 × 10 −11 mol cm −2. Surface modifications could be extrapolated to other carbons, and the materials could be employed for different potential applications such as photocatalysis, amperometric sensors, fuel cells, and supercapacitors.

Theoretical study on the electronic structure nature of single and double walled carbon nanotubes and its role on the electron transport

“…[52] ReaxFF methodology incorporates a shielding term in the vdW and Coulomb energy contributions when an excess of short-distance, nonbonded interactions are present, and all discontinuities in the nonbonding interaction energies are banned using a seventh-order taper function. [53] Periodic boundary conditions were considered in the simulations with box sizes of 27.33 × 27.33 × 31.0 Å for the systems (10,10)@ (15,15), a box size of 26.33 × 26.56 × 31.0 Å for (9,9)@ (14,14), and 25.33 × 25.56 × 31.0 Å for (14,14)@ (15,0). Finally, a box size of 18.33 × 18.56 × 31.0 Å were considered for the rest of the systems.…”

“…Case C1 are those DWCNTs in which no changes in the predicted nature (metallic or semiconductor) are expected, when the internal tubes change from armchair to zigzag type. When outer CNTs are (9,9), the generated DWCNTs will remain as semiconductor assemblies. Experiments on one-dimensional semiconductor wires, have been interpreted by using Luttinger-liquid theory, [36] but an unequivocal verification of the theoretical predictions has not yet been obtained.…”

“…Here, internal diameter of CNTs armchair (4,4) and zigzag type (7,0) are relevant due to curvature effects. Whereas, for external CNTs (14,14), DWCNTs will be metallic independently of selected configuration for internal CNTs either (9,9) (15,0). Electron transport in conductors including metallic CNTs are usually well described by Fermi-liquid theory, which presumes that the energy states of the electrons near the Fermi level E F are not qualitatively altered by Coulomb interactions, see Bockrath et al [36] In Figure S4 Blumenstein et al [67] and Wang et al [68] have showed that for i-DWCNTs the coupling is negligible between lowest energy subbands, but it becomes important as the higher subbands become populated.…”

“…After our MD simulations were performed, we were able to predict stability in SWCNT (6,6) and (9,0) systems, considering open-ended, one side-capped, and both sides-capped (see Figure 18A-D). Nevertheless, the corresponding DWCNT (6,6)@(9,0) proved to be highly unstable.…”

“…This is routinely performed in order to improve capacitive properties for applications in energy storage. [9] Some theoretical studies on DWCNT systems have been carried out in the last years, such as that of Moradian et al, [10] who reported the effect of the interwall distance between two concentric CNT: semiconducting and metallic characters were found by considering four cases: metal/metal, metal/semiconductor, semiconductor/metal, and semiconductor/semiconductor (inner/outer). In the first three cases, it was F I G U R E 1 Graphene honeycomb network in green with the lattice vectors a 1 and a 2 .…”