Enhanced hydrogen storage performance of graphene nanoflakes doped with Cr atoms: a DFT study

Density Functional Theory-Based Approaches to Improving Hydrogen Storage in Graphene-Based Materials

Various technologies have been developed for the safe and efficient storage of hydrogen. Hydrogen storage in its solid form is an attractive option to overcome challenges such as storage and cost. Specifically, hydrogen storage in carbon-based structures is a good solution. To date, numerous theoretical studies have explored hydrogen storage in different carbon structures. Consequently, in this review, density functional theory (DFT) studies on hydrogen storage in graphene-based structures are examined in detail. Different modifications of graphene structures to improve their hydrogen storage properties are comprehensively reviewed. To date, various modified graphene structures, such as decorated graphene, doped graphene, graphene with vacancies, graphene with vacancies-doping, as well as decorated-doped graphene, have been explored to modify the reactivity of pristine graphene. Most of these modified graphene structures are good candidates for hydrogen storage. The DFT-based theoretical studies analyzed in this review should motivate experimental groups to experimentally validate the theoretical predictions as many modified graphene systems are shown to be good candidates for hydrogen storage.

Design and implementation of humidity sensor based on carbon nitride modified with graphene quantum dots

Relative humidity (RH) is one of the most important factors that deserve intensive study because of its impact on many aspects of life. In this work humidity sensor based on carbon nitride / graphene quantum dots (g-C3N4/GQDs) nanocomposites have been developed. The structure, morphology and composition properties of the g-C3N4/GQDs were investigated and analyzed by XRD, HR-TEM, FTIR, UV-Vis, Raman, XPS and BET surface area. The average particle size of GQDs was estimated from XRD to be 5 nm and confirmed using HRTEM. The HRTEM images prove that the GQDs are attached to the external surface of the g-C3N4. The measured BET surface area was found to be 216 m2/g, 313 m2/g, and 545 m2/g for GQDs, g-C3N4, and g-C3N4/GQDs respectively. The d-spacing and crystallite size were estimated from XRD and HRTEM and found in a good matching. The humidity sensing behavior of g-C3N4/GQDs was measured in a wide span of humidity from 7% up to 97% RH under different testing frequencies. The obtained results demonstrate good reversibility and fast response/recovery time. The implemented sensor exhibits a great application prospect in humidity alarm devices, automatic diaper alarms, and breath analysis, which have advantages such as strong anti-interference capability, low cost, and easy to use.

DFT study of hydrogen interaction with transition metal doped graphene for efficient hydrogen storage: effect of d-orbital occupancy and Kubas interaction

Hydrogen adsorption on pristine graphene (PG), graphene with defect (GD), and transition metal (TM) (Ag, Au, Cu, and Fe) doped graphene is systematically investigated for potential hydrogen storage using density functional theory. The stability of the TM atom doped graphene has been analysed by studying the binding energy and the electron density distribution. The TM atom-doped GD shows better binding energy and electron density overlap than PG; therefore, the TM/GD system has been considered and analysed for hydrogen adsorption. The hydrogen adsorption property is studied by examining the adsorption energy, mode of H₂, density of states (DOS), charge density difference, and Löwdin charges before and after adsorption to find a better TM/GD system for hydrogen storage. The Fe/GD system shows higher hydrogen adsorption energy and hydrogen in its stable Kubas mode. Furthermore, two to five H₂ molecule adsorption and desorption is studied. The increase in the number of H₂, which changes the DOS at the Fermi level, suggests that one can predict H₂ concentration by measuring conductivity changes. The present work is focused on studying the interaction between H₂ and TM/GD systems, which will help understand the basic adsorption mechanism for practical hydrogen storage.

Improvement of the hydrogen storage performance of t-graphene-like two-dimensional boron nitride upon selected lithium decoration

In recent years, search for applicable bidimensional (2D) hydrogen storage materials with high capacity and excellent H₂ physisorption properties has attracted considerable attention from scientists and researchers. According to the rational design, and using first-principles calculations, we propose a t-graphene-like boron nitride monolayer (t-B₄N₄) for hydrogen storage application by replacing C atoms in t-graphene with B and N atoms. The thermal stability and polarization mechanisms of lithium atoms adsorbed at the center of octagons on the t-B₄N₄ system were evaluated at 300 K using ab initio molecular dynamics (AIMD) calculations. Moreover, Li-decorated double-sided t-B₄N₄ can store up to 32H₂ molecules with an average hydrogen adsorption energy of 0.217 eV per H₂ and a maximum hydrogen storage capacity of 12.47 wt%. The reversibility of adsorbed hydrogen was checked and the calculated desorption temperature was 161 K, much higher than the critical point for hydrogen. Based on diffusion barriers, the H₂ molecule diffusion kinetics is faster on the t-B₄N₄ surface than that on t-graphene and graphene.

Ti4-Decorated B/N-doped graphene as a high-capacity hydrogen storage material: a DFT study

The adsorption properties of the hydrogen atom on our newly designed materials were investigated using density functional theory (DFT) calculations, focusing on the role of dopants in modulating the binding properties of the metal. We proposed decorating Ti₄ on pristine, B- and N-doped graphene surfaces for preparing a large-capacity hydrogen-storage device. Computational results indicate that the doping of B on graphene enhances the interaction between the metal cluster and the supporting substrate with a very strong binding energy of -6.45 eV, which is the strongest interaction among our proposed catalysts. This binding energy prevents the aggregation and formation of Ti-metal clusters. Dissociative chemisorption of the first H₂ molecule occurs on all materials. Metal hydrides preferentially exhibit strong hybridization between the H-1s and Ti-3d orbitals. Furthermore, Ti₄ decorated B-graphene is the most effective, with a high capacity of hydrogen adsorption which could be released under practical conditions. We confirmed that eight H₂ molecules could stably adsorb on Ti₄/BGr with six reversible hydrogen adsorptions. Our proposed B-doped graphene-based material, Ti₄/BGr, offers high cluster-stability on the substrate with high-capacity hydrogen storage compared to various other surfaces in the previous work. Therefore, Ti₄ decorated B-graphene is a promising candidate material for use as a reversible hydrogen storage material.