Transition metal (TM) atoms bound to fullerenes are proposed as adsorbents for high density, room temperature, ambient pressure storage of hydrogen. C60 or C48B12 disperses TMs by charge transfer interactions to produce stable organometallic buckyballs (OBBs). A particular scandium OBB can bind as many as 11 hydrogen atoms per TM, ten of which are in the form of dihydrogen that can be adsorbed and desorbed reversibly. In this case, the calculated binding energy is about 0.3 eV/H(2), which is ideal for use on board vehicles. The theoretical maximum retrievable H2 storage density is approximately 9 wt %.

We report an effective solvent engineering process to enable controlled perovskite crystal growth and a wider window for processing uniform and dense methyl ammonium lead iodide (MAPbI3) perovskite films. Planar heterojunction solar cells fabricated with this method demonstrate hysteresis-free performance with a power conversion efficiency around 10%. The crystal structure of an organic-based Pb iodide intermediate phase is identified for the first time, which is critical in controlling the crystal growth and optimizing thin film morphology.

First-principles density functional and quantum Monte Carlo calculations of light-element doped fullerenes reveal significantly enhanced molecular H2 binding for substitutional B and Be. A nonclassical three-center binding mechanism between the dopant and H2 is identified, which is maximized when the empty p(z) orbital of the dopant is highly localized. The calculated binding energies of 0.2-0.6 eV/H2 is suited for reversible hydrogen storage at near standard conditions. The calculated H2 sorption process is barrier-less, which could also significantly simplify the kinetics for the storage.

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The crystal and electronic band structures of CuxS(1.25 < x ≤ 2) are systematically studied using the density-functional theory method. For Cu2S, all the three chalcocite phases, i.e., the low-chalcocite, the high-chalcocite, and the cubic-chalcocite phases have direct band gaps around 1.3–1.5 eV, with the low-chalcocite being the most stable one. However, Cu vacancies can form spontaneously in these compounds, causing instability of Cu2S. We find that under Cu-rich condition, the anilite Cu1.75S is the most stable structure. It has a predicted band gap of 1.4 eV and could a promising solar cell absorber.

Exploring earth‐abundant bifunctional electrocatalysts with high efficiency for water electrolysis is extremely demanding and challenging. Herein, density functional theory (DFT) predictions reveal that coupling Ni with Ni3C can not only facilitate the oxygen evolution reaction (OER) kinetics, but also optimize the hydrogen adsorption and water adsorption energies. Experimentally, a facile strategy is designed to in situ fabricate Ni3C nanosheets on carbon cloth (CC), and simultaneously couple with Ni nanoparticles, resulting in the formation of an integrated heterostructure catalyst (Ni–Ni3C/CC). Benefiting from the superior intrinsic activity as well as the abundant active sites, the Ni–Ni3C/CC electrode demonstrates excellent bifunctional electrocatalytic activities toward the OER and hydrogen evolution reaction (HER), which are superior to all the documented Ni3C‐based electrocatalysts in alkaline electrolytes. Specifically, the Ni–Ni3C/CC catalyst exhibits the low overpotentials of only 299 mV at the current density of 20 mA cm−2 for the OER and 98 mV at 10 mA cm−2 for the HER in 1 m KOH. Furthermore, the bifunctional Ni–Ni3C/CC catalyst can propel water electrolysis with excellent activity and nearly 100% faradic efficiency. This work highlights an easy approach for designing and constructing advanced nickel carbide‐based catalysts with high activity based on the theoretical predictions.

Despite the scientific importance of semiconductor quantum dots (QDs), little is known about their structure other than the bulk form. Here, we show that one can join segments of tetravalent semiconductors into a seamless icosahedron. Calculations for Si show that pristine icosahedral QDs are more stable than bulklike ones for diameter d < 5 nm. Hydrogenated icosahedral quantum dots (IQDs) could also be stable and more atomiclike with larger level spacing and fivefold orbital degeneracy due to the I h symmetry not possible in the bulk. Experimental feasibility toward synthesizing the IQDs in Si and diamond is also discussed.In regard to the quantum effects in a semiconductor quantum dot (QD), symmetry plays a unique role. For instance, the breakdown of the translational symmetry in a truncated crystal leads to the quantization of the electronic states. Higher point-group symmetry often leads to higher orbital degeneracy, thus further enhancing the discreteness of the density of states (DOS) without actually altering physical forces. It is customary to assume that a QD has, at its best, the point-group symmetry of the corresponding bulk, to which certain selection rules apply. Moreover, it is often assumed that a QD takes the bulk structure until it approaches the cluster limit of less than a hundred atoms [1]. There is, however, no a priori reason to believe either of the above to be true. In fact, in a wide range of substances of nanometer sizes, icosahedron, which has the highest point-group symmetry but is forbidden in any periodic crystal, has been observed. These include, noticeably, many viruses [2], inert-gas elements [3], fullerenes [4], metals [5], and certain oxides [6]. In all these cases, surface energy minimization holds the key for the icosahedral stability. Because of their directional bonding, the energy of a tetrahedrally coordinated semiconductor surface depends strongly on the surface orientation. It is thus also likely for the structure of a semiconductor QD to deviate from bulk, should the tetrahedral coordination permit.In this Letter, we show by first-principles calculations that, over the size range of scientific and technological importance, tetravalent semiconductor QDs also stabilize in the icosahedral form. For example, pristine silicon icosahedra are more stable than bulklike QDs for d < 5 nm or N < 2500. Calculations on hydrogenated Si icosahedra further reveal (i) fivefold orbital degeneracy due to the I h symmetry (with 120 group operations instead of 48 for cubic structures), which results in (ii) significantly increased level spacing and peak sharpness, and (iii) enhanced spatial localization of the electronic states due to a dodecahedral core. All indicate that the electronic properties of the icosahedral quantum dots (IQDs) are more atomiclike than bulklike QDs.Calculations were carried out using the densityfunctional formalism within the local density approximation (LDA) and ultrasoft pseudopotentials, as implanted in the Vienna ab initio simulation (VASP) package [7]. We used...

Transition-metal (TM) boride and carboride nanostructures are studied as model organometallic materials for hydrogen storage. The dispersed TM atoms function as H 2 sorption centers on the surface of the boron or carbon−boron substrate. The flexibility offered in the variety of possible structures permits the study of the effect of the TM−TM distance on the storage capacity. When the TMs are too close to one another, TM−TM bonding reduces the capacity. Even when separated by distances larger than the normal TM−TM bond length, delocalization of TM valence electrons can still lower the hydrogen capacity. An optimal TM−TM distance for the structural motifs studied here is ∼6 Å. Our study also permitted the evaluation of new TM boride nanostructures. We predict a low-energy single-walled scandium triboride (ScB 3 ) nanotube that can bind ∼6.1 wt % hydrogen with a binding energy of 22∼26 kJ/mol.