Graphene-analogous low-dimensional materials

Graphene-based materials: Synthesis and gas sorption, storage and separation

Searching for reversible hydrogen storage materials operated under ambient conditions is a big challenge for material scientists and chemists. In this work, using density functional calculations, we systematically investigated the hydrogen storage properties of the two-dimensional (2D) Ti2C phase, which is a representative of the recently synthesized MXene materials ( ACS Nano 2012 , 6 , 1322 ). As a constituent element of 2D Ti2C phase, the Ti atoms are fastened tightly by the strong Ti-C covalent bonds, and thus the long-standing clustering problem of transition metal does not exist. Combining with the calculated binding energy of 0.272 eV, ab initio molecular dynamic simulations confirmed the hydrogen molecules (3.4 wt % hydrogen storage capacity) bound by Kubas-type interaction can be adsorbed and released reversibly under ambient conditions. Meanwhile, the hydrogen storage properties of the other two MXene phases (Sc2C and V2C) were also evaluated, and the results were similar to those of Ti2C. Therefore, the MXene family including more than 20 members was expected to be a good candidate for reversible hydrogen storage materials under ambient conditions.

MXene: a new family of promising hydrogen storage medium.

Since the first report of using micromechanical cleavage method to produce graphene sheets in 2004, graphene/graphene-based nanocomposites have attracted wide attention both for fundamental aspects as well as applications in advanced energy storage and conversion systems. In comparison to other materials, graphene-based nanostructured materials have unique 2D structure, high electronic mobility, exceptional electronic and thermal conductivities, excellent optical transmittance, good mechanical strength, and ultrahigh surface area. Therefore, they are considered as attractive materials for hydrogen (H2) storage and high-performance electrochemical energy storage devices, such as supercapacitors, rechargeable lithium (Li)-ion batteries, Li–sulfur batteries, Li–air batteries, sodium (Na)-ion batteries, Na–air batteries, zinc (Zn)–air batteries, and vanadium redox flow batteries (VRFB), etc., as they can improve the efficiency, capacity, gravimetric energy/power densities, and cycle life of these energy storage devices. In this article, recent progress reported on the synthesis and fabrication of graphene nanocomposite materials for applications in these aforementioned various energy storage systems is reviewed. Importantly, the prospects and future challenges in both scalable manufacturing and more energy storage-related applications are discussed.

Graphene‐Based Nanocomposites for Energy Storage

Based on first-principles plane wave calculations, we showed that Ca adsorbed on graphene can serve as a high-capacity hydrogen storage medium, which can be recycled by operations at room temperature. Ca is chemisorbed by donating part of its $4s$ charge to the empty ${\ensuremath{\pi}}^{\ensuremath{\ast}}$ band of graphene. At the end the adsorbed Ca atom becomes positively charged and the semimetallic graphene changes into a metallic state. While each of the adsorbed Ca atoms forming the $(4\ifmmode\times\else\texttimes\fi{}4)$ pattern on the graphene can absorb up to five ${\text{H}}_{2}$ molecules, hydrogen storage capacity can be increased to $8.4\text{ }\text{wt}\text{ }%$ by adsorbing Ca to both sides of graphene and by increasing the coverage to form the $(2\ifmmode\times\else\texttimes\fi{}2)$ pattern. Clustering of Ca atoms is hindered by the repulsive Coulomb interaction between charged Ca atoms.

/pdf/hydrogen-storage-of-calcium-atoms-adsorbed-on-graphene-first-41jgrgynqp.pdf

Hydrogen storage of calcium atoms adsorbed on graphene: First-principles plane wave calculations

Based on first-principles density functional theory, we show that Li-doped B2C graphene can serve as a high-capacity hydrogen storage medium with the gravimetric density of 7.54 wt %. The present results indicate that the strong binding of Li onto the substrate comes from the hybridizations of B 2p and C 2p orbitals with the partial occupancy of Li 2p orbitals. Both the polarization mechanism and the orbital hybridizations contribute to the adsorption of H2 molecules and the resulting adsorption energy is in the range of 0.12–0.22 eV/H2. The system reported here is favorable for the reversible hydrogen adsorption/desorption at the room temperature.

Li-doped B2C graphene as potential hydrogen storage medium

We show that a Li-coated zigzag (2,2) boron nanotube can serve as a high-capacity hydrogen storage medium using first-principles density functional theory. The present results indicate that the radial deformation of a Li-coated boron nanotube can strengthen the binding of Li atoms to the boron nanotube due to the hybridization between Li-$p$ orbitals and B-$p$ orbitals. Interestingly, the induced large surface curvature of the Li-coated nanotube can make the ${\mathrm{H}}_{2}$ molecules directly adsorbed on the nanotube. Through the electronic analysis we find that not only the polarization mechanism but also the orbital hybridization between H-$s$ orbitals and Li-$p$ (B-$p$) orbitals act on the adsorbed ${\mathrm{H}}_{2}$ molecules. The Li-coated zigzag (2,2) boron nanotube reported here can store hydrogen up to 7.94 wt% with the adsorption energy of 0.12--0.20 eV/H${}_{2}$ and the whole system is favorable for the reversible hydrogen adsorption/desorption at ambient conditions.

Radial deformation-induced high-capacity hydrogen storage in Li-coated zigzag boron nanotubes

The capacity of Ti-capped sp carbon atomic chains for use as hydrogen storage media is studied using first-principles density functional theory. The Ti atom is strongly attached at one end of the carbon chains via d-p hybridization, forming stable TiCn complexes. We demonstrate that the number of adsorbed H2 molecules on Ti through Kubas interactions depends upon the chain types. For polyyne (n even) or cumulene (n odd) structures, each Ti atom can hold up to five or six H2 molecules, respectively. Furthermore, the TiC5 chain effectively terminated on a C20 fullerene can store hydrogen with an optimal binding energy of 0.52 eV per H2 molecule. Our results reveal a possible way to explore high-capacity hydrogen storage materials in truly one-dimensional carbon structures.

Titanium-capped carbon chains as promising new hydrogen storage media

Acetalized starch-based nanoparticles stabilized acid-sensitive Pickering emulsion as a potential antitumor drug carrier.

Rod-like particles have attracted increasing attention because of their unique shape-dependent properties, which enable their superior performance compared to their isotropic counterparts. Thus, rod-like particles have potential applications in many fields, especially in biomedicine. However, the fabrication of uniform rod-like particles is challenging because of the principle of interfacial energy minimization. Herein, we present a facile, rapid, and cost-effective strategy for preparing starch-based microrods with tunable aspect ratios via shear-assisted antisolvent-induced nanoprecipitation and solidification. The preformed spherical particles swollen by the mixed solvent were elongated by the shear force and solidified in rod-like shape by antisolvent induction. The resulting starch-based microrods can encapsulate hydrophobic active substances and be modified with functional groups, indicating their potential applications as drug carriers and biologically active materials. The formation mechanism of the starch-based microrods discovered in this study provides a new perspective on the fabrication of rod-like polymer particles.

Facile Fabrication of Starch-Based Microrods by Shear-Assisted Antisolvent-Induced Nanoprecipitation and Solidification.

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