Understanding bond formation and its impact on the capacitive properties of SiW12 polyoxometalates adsorbed on functionalized Carbon Nanotubes

Abstract

In the last decade, a large number of studies at the experimental level in electrochemical systems for energy storage devices have been performed. However, theoretical approaches are highly desirable to understand the physicochemical properties giving rise to energy storage phenomena. This work was intended to provide insights into the $in$ $silico$ design of novel nanocomposite materials formed by the Keggin polyoxometalate SiW12 anchored to an organic functional group $\varphi-X$ (with $X = -NH2, -OH, -COH$ and $-COOH$), linked to a carbon nanotube. In these systems, the Density of States around the Fermi level is enhanced, giving the composite material the capacity of facile electron transport that may be determinant at the charge/discharge cycling performed in energy storage devices. Charge transfer at the composite materials under study is greatest for the $\varphi-COOH$ functional group, yielding an attraction with the SiW12 cluster of the same order of magnitude as that of covalent nature. The rest of the functional groups induce a non-covalent interaction of the electrostatic type, mediated by a van der Waals attraction. Our proposed methodology may represent a tool to develop novel electrode materials that may improve the performance on energy storage devices, such as supercapacitors or Li$-$ion batteries.