Nitrogen-doped carbon nanomaterials are known to exhibit good electrocatalytic activity for the oxygen reduction reaction (ORR). However, the structure of the ORR active site and optimum content of nitrogen in the carbon lattice for ORR activity remains unknown. In this study, a series of vertically aligned carbon nanotubes (VA-CNTs) with a surface nitrogen concentration of 0, 4.3, 5.6, 8.4, and 10.7 atom % is prepared by the alumina template technique and characterized with XRD, Raman spectroscopy, SEM, and XPS. Electrocatalytic ORR activity is investigated by rotating disk electrode (RDE) voltammetry. Among them, VA-CNTs with a nitrogen concentration of 8.4 atom % exhibited the best ORR performance. This is ascribed to a greater number of pyridinic-type nitrogen sites. The good performance of less expensive nitrogen-doped CNTs makes the ORR electrodes a viable alternative to platinum for energy conversion device applications.

By means of density functional theory computations, we systematically investigated the adsorption and diffusion of lithium on the recently synthesized VS 2 monolayer, in comparison with MoS 2 monolayer and graphite. Intrinsically metallic, VS 2 monolayer has a higher theoretical capacity (466 mAh/g), a lower or similar Li diffusion barrier as compared to MoS 2 and graphite, and has a low average opencircuit voltage of 0.93 V (vs Li/Li + ). Our results suggest that VS 2 monolayer can be utilized as a promising anode material for Li ion batteries with high power density and fast charge/ discharge rates.

process is used to realize the transformation from N 2 to NH 3 , which consumes massive amounts of energy and causes serious pollutions. In comparison, the electrochemical reduction of N 2 under mild conditions can significantly reduce the energy input and simplify the reactor design, and thus is a quite promising strategy for NH 3 production. [3] So far, transition metals, such as Ru, Rh, Au, Pt, Ni, Ti, Fe, and Cu, have been widely studied as catalysts for N 2 reduction reaction (NRR) to NH 3 . [4] To reduce the metal usages in the catalysts, ideally single atoms could be a choice. However, the surface free energy of metals increases significantly with decreasing the particle size, and metal atoms tend to aggregate to small clusters. Thus, inhibiting the metal atoms from diffusion and agglomeration is critical to ensure their high stabilization in the processes of catalyst design and synthesis. Single-atom catalysts (SACs), first reported by Qiao et al. [5] and featured with well-defined and uniformly dispersed single atoms on support, are providing us an unprecedented solution. Such catalysts not only maximize the efficiency of metal usage to 100% and significantly reduce the metal cost, especially for noble metal catalysts, such as Au, Pt, Ir, and Pd, but also provide great potentials to achieve high activity and selectivity due to the high ratio of the low-coordinated metal atoms. [6] These advantages distinguish SACs from their corresponding bulk materials and nanoparticles, and SACs have already emerged as a new class of catalyst for a variety of important reactions, [7] such as CO oxidation, [5] methanol partial oxidation, [8] water-gas shift, [9] selective hydrogenation of 1,3-butadiene, [10] some important organic reactions, such as oxidation, hydrogenation, CC coupling and reforming, [11] electrocatalytic, [12] or photocatalytic reactions. [13] To achieve a good SAC, we not only need suitable single atoms, but also need to deliberately select an appropriate substrate that can strongly interact with the metal atoms. Since the successful synthesis of graphene in 2004, [14] many 2D materials have been widely utilized as promising substrates for metal atoms in catalysts due to their unique physical and chemical properties, such as high specific surface area, good mechanical and thermal stability. [15] However, pristine graphene is not The development of low-cost and efficient electrocatalysts for nitrogen reduction reaction (NRR) at ambient conditions is crucial for NH 3 synthesis and provides an alternative to the traditional Harber-Bosch process. Herein, by means of density functional theory (DFT) computations, the catalytic performance of a series of single metal atoms supported on graphitic carbon nitride (g-C 3 N 4 ) for NRR is evaluated. Among all the candidates, the Gibbs free energy change of the potential-determining step for five single-atom catalysts (SACs), namely Ti, Co, Mo, W, and Pt atoms supported on g-C 3 N 4 monolayer, is lower than that on the Ru(0001) stepped surface. In particular, ...

By means of density functional theory computations, we systematically investigated the adsorption and diffusion of Li on the 2-D MoS2 nanosheets and 1-D zigzag MoS2 nanoribbons (ZMoS2NRs), in comparison with MoS2 bulk. Although the Li mobility can be significantly facilitated in MoS2 nanosheets, their decreased Li binding energies make them less attractive for cathode applications. Because of the presence of unique edge states, ZMoS2NRs have a remarkably enhanced binding interaction with Li without sacrificing the Li mobility, and thus are promising as cathode materials of Li-ion batteries with a high power density and fast charge/discharge rates.

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