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Electrode materials for energy storage devices based on carbon materials have shown to be a reliable choice in supercapacitors or Li-ion batteries. The development of novel carbon materials may improve the performance of such devices and the use of eco-friendly materials from biomass waste may provide a breakthrough in the area. In this study, we give theoretical insights into the in silico design of carbon materials based on lignocellulosic molecules present in the waste residues. We performed pyrolysis-simulated calculations at the ReaxFF level with the Adler's softwood lignin model as the precursor material. Different models were implemented by randomly combining massive lignocellulosic molecules. The simulated pyrolysis of the lignocellulosic components was performed starting with a heating step from room temperature to a temperature limit of 1280 K, followed by a stabilization period. The reaction was subjected to quenching, and finally to a period of thermal equilibrium. The formed char was characterized as nanoporous carbon according to its density, radial distribution function and pore size distributions. Comparison of these results with our available experimental data revealed reasonable agreement. This may aid in the design of carbon electrodes for energy storage devices and applications in which stable and predictable properties are desirable.

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., Comment: Research article. 43 pages, 5 figures

This article contains data on nanoporous carbon materials coming from lignocellulosic components. Such data is directly related to the research paper “Insights into the design of carbon electrodes coming from lignocellulosic components pyrolysis with potential application in energy storage devices: A combined in silico and experimental study” [1]. In this work, the geometrical parameters of nanoporous carbon systems were found with Molecular Dynamics (MD) simulations at the ReaxFF level. The tridimensional structures of such carbon systems are given in Cartesian coordinates. They were computed at different heating rates, simulating the conditions observed in pyrolysis processes of Agave angustifolia leaves, which were carried out in a solar furnace. Nanoporous carbon systems are characterized with radial distribution functions (RDF) and ring distribution profiles. Keywords: ReaxFF simulations, Energy storage, Pyrolysis, Nanoporous carbon

Nanocarbon materials have attracted attention in the last decade due to their broad range of applications in solid-state devices. Particularly, nanocarbon has intensely been implemented in energy storage systems such as Li-ion batteries and supercapacitors. Furthermore, it has also been shown that the structural features of carbon substrates are determinant on the final characterization as an electrode of such kinds of devices. Different experimental approaches have traced the development of carbon substrates as electrodes on the improvement of the performance of a device to store electronic charge. Nevertheless, several processes involved in the description of charge retention are unclear or they are subject to debate. Consequently, the intense study at the fundamental level of such processes plays an important role to fully understand the mechanism behind charge storage, such as the nature of bonding with other substrates as metallic oxides, or the role of ion transport at the carbon interface. In this sense, the present chapter is intended to provide a comprehensive review of relevant experimental results that have inspired theoreticians to apply state-of-the-art methodologies to give insight into the physicochemical phenomenology resulting from charge retention. Furthermore, we also reviewed those cases where density functional theory and molecular dynamics simulations act as reliable schemes to be implemented on the study of structural features and electronic structure properties of carbon and its interaction with metallic oxides. We also present a review of theoretical results emerging in our group, and their intersections with data coming from the laboratory. Finally, we introduce a proposal composed of different avenues that a multidisciplinary group may be able to track in order to provide new insights to gain a profound knowledge of carbon-based electrodes at the atomistic level, and to coordinate the design of novel materials aimed to store energy with higher efficiencies and ecofriendly properties.

Using DFT theory, we calculated theoretically photoluminescence (PL) spectra of double-walled carbon nanotubes (DWCNTs). Using the supercomputer (LNS) tool, the photoluminescence spectra for eight double-walled nanotubes were calculated with the Gaussian09 software; the DWCNTs built are of the armchair/armchair type, (3,3)/(2,2), (6,6)/(3,3), (8,8)/(4,4), (10,10)/(5,5), (12,12)/(6,6), (14,14)/(7,7), (16,16)/(8,8) and (18,18)/(9,9). The calculations were obtained taking into account different DWCNT lengths ranging from 4.9 A to 23.4 A when changing the chirality (n, m) of the double-walled carbon nanotubes, as well as we considered the increase in their inter-radial distance ranging from 0.18 ≤ dR ≤ 0.62 nm. The objective of this work focuses on investigating the DWCNTs PL considering different atomic arrangements. The calculation was performed at a DFT level in which we used the Generalized Gradient Approximation (GGA) to establish the molecular geometries and the fundamental state energies. To obtain the results of the PL spectra, the DWCNTs were optimized in their ground state, with the hybrid function CAM-B3LYP, which is a mixed functional exchange and correlation and the base set that was used is the 6–31 G.

Correlations among atomic structure, chemical reactivity, charge transfer and electronic structure properties were investigated in nanoporous carbon at different mass densities. The model structures have been generated by a heat-quench procedure using Density Functional Theory calculations and first-principles quantum molecular dynamics simulations. Reactive points seem to be highly dependent of the local structure of the material. The results showed that sponge-like nanoporous carbons are good candidates to graft polyoxometalates since they presented a stronger interaction with the carbon substrate. The charge transfer is from the nanoporous carbon to the polyoxometalate and a covalent interaction was observed for a density of 0.75 g/cm3. Our materials developed an electronic band around the Fermi level.

In systems in atomic and nano scales such as clusters or agglomerates constituted of particles from a few to less than one hundred of atoms, quantum confinement effects are very important. Their optical and electronic properties are often dependent on the size of the systems and the way in which the atoms in these clusters are bonded. Generally, these nano-structures display optical and electronic properties significantly different of those found in corresponding bulk materials. Silicon agglomerates found in Silicon Rich Oxide (SRO) films have optical properties, which have reported as depended directly on nano-crystal size. Furthermore, the room temperature photoluminescence (PL) of Silicon Rich Oxides (SRO) has repeatedly generated a huge interest due to their possible applications in optoelectronic devices. However, a plausible emission mechanism has not yet widespread acceptance of the scientific community. In this research, we employed the Density Functional Theory with a functional B3LYP and a basis set 6 - 31G* to calculate the optical and electronic properties of small (six to ten silicon atoms) and medium size clusters of silicon (constituted of eleven to fourteen silicon atoms). With the theoretical calculation of the structural and optical properties of silicon clusters, it is possible to evaluate the contribution of silicon agglomerates in the luminescent emission mechanism experimentally found in thin SRO films.