By means of density functional theory computations, we systematically investigated the adsorption and diffusion of lithium on the recently synthesized VS2 monolayer, in comparison with MoS2 monolayer ...and graphite. Intrinsically metallic, VS2 monolayer has a higher theoretical capacity (466 mAh/g), a lower or similar Li diffusion barrier as compared to MoS2 and graphite, and has a low average open-circuit voltage of 0.93 V (vs Li/Li+). Our results suggest that VS2 monolayer can be utilized as a promising anode material for Li ion batteries with high power density and fast charge/discharge rates.
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 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.
In recent years, two-dimensional (2D) materials, including graphene and inorganic graphene analogs (IGAs), have been the subject of intensive studies due to their novel chemical and physical ...properties. With apparent high surface-to-volume ratio, 2D materials are promising electrode candidates for lithium ion batteries (LIBs). Compared with three-dimensional bulk crystals, 2D materials have superior structural characteristics, and thus can exhibit higher specific capacity and better high-rate stability. In particular, composites consisting of graphene and IGAs could have enhanced electrochemical performances due to the specific synergic effects, which open up new frontiers in fundamental science and technology. Although the explorations of using IGAs for lithium storage have begun very recently, a timely overview in this field is necessary for developing improved electrode candidates. In this feature article, we summarize the ongoing efforts and studies from both experimental and theoretical communities on developing graphene and IGAs as LIB electrodes. Compared with graphene, we put more emphasis on IGAs, such as transition metal oxides, dichalcogenides, and MXenes, and illustrate the significant advantages of IGAs as electrodes. We also show that due to the effective synergic interactions between graphene and IGAs, their composites step further to achieve reversible high-capacity LIBs. Finally, we discuss the problems and limitations for the practical application of 2D materials to LIBs.
Very recently, intrinsically metallic B-substituted silicenes, namely, H-BSi3 and R-BSi3 (H and R denote the hexagonal and rectangular symmetry), have been predicted as the global minimum structures ...of the BSi3 monolayer (J. Phys. Chem. C 2014, DOI: 10.1021/jp507011p). With unusual planar geometry and better electronic conductivity relative to the buckled and semimetallic pristine silicene sheet, the B-substituted silicenes are expected to have good applications in high capacity lithium-ion batteries (LIBs) anodes. By means of density functional theory (DFT) computations, we systematically investigated the adsorption and diffusion of Li on H-BSi3 and R-BSi3, in comparison with silicene and graphite. Their exceptional properties, including good electronic conductivity, very high theoretical charge capacity (1410 and 846 mA·h/g for single- and double-layer, respectively), fast Li diffusion, and low open-circuit voltage (OCV), suggest that the BSi3 silicene could serve as a promising high capacity and fast charge/discharge rate anode material for LIBs.
Graphene-supported Pt and Pt–Au alloy electrocatalysts are prepared by ethylene glycol reduction method and characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), ...transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). XRD reveals the face-centered cubic structure of Pt in the materials. SEM and TEM images show the good spatial distribution of metal nanoparticles on layered graphene sheets. EDX reveals that the average composition of elements in the Pt–Au alloy catalyst is approximately 1:1. Electrocatalytic performance of the prepared materials toward formic acid oxidation (FAO) is investigated using cyclic voltammetry. FAO activity of the Pt–Au/graphene is found to be ten times higher than that of Pt/graphene. The prepared electrocatalysts are used as anode in a direct formic acid fuel cell and tested at 303 and 333 K. An increase in the performance with increasing temperature is observed. A maximum power density of 185, 70, and 53 mW/cm2 is observed with Pt–Au/graphene, Pt/graphene, and commercial Pt/C anodes, respectively, at 333 K. The high electrocatalytic performance of Pt–Au/graphene is attributed to the change in the electronic structure of Pt by the presence of alloying element, Au.
Display omitted
•Layer-by-layer MoS2/rGO hybrids were prepared by rGO involved lithiation-exfoliation method.•This hybrid exhibited enhanced electrochemical performances due to the existence of ...rGO.•The roles of rGO in different charging/discharging processes were interpreted by computations.
Two-dimensional MoS2 shows great potential for effective Li storage due to its good thermal and chemical stability, high theoretical capacity, and experimental accessibility. However, the poor electrical conductivity and the restacking tendency significantly restrict its applications to lithium ion batteries (LIBs). To overcome these problems, we introduced reduced graphene oxides (rGO) to the intercalation-exfoliation preparation process of few-layered MoS2 and obtained layer-by-layer MoS2/rGO hybrids. With the addition of rGO, the restacking of MoS2 layers was apparently inhibited, and MoS2 with 1∼3 layers was obtained in the composite. Due to the positive role of rGO, MoS2/rGO hybrids exhibited highly enhanced cyclic stability and high-rate performances as LIB anodes in comparison with bare MoS2 layers or bulk MoS2. Moreover, the experimental results were well interpreted through density functional theory computations.
This review deals with the main mechanisms of action exerted by antagonistic bacteria, such as competition for space and nutrients, suppression via siderophores, hydrolytic enzymes, antibiosis, ...biofilm formation, and induction of plant resistance. These mechanisms inhibit phytopathogen growth that affects postharvest fruit since quality and safety parameters are influenced by the action of these microorganisms, which cause production losses in more than 50% of fruit tree species. The use of synthetic fungicide products has been the dominant control strategy for diseases caused by fungi. However, their excessive and inappropriate use in intensive agriculture has brought about problems that have led to environmental contamination, considerable residues in agricultural products, and phytopathogen resistance. Thus, there is a need to generate alternatives that are safe, ecological, and economically viable to face this problem. Phytopathogen inhibition in fruit utilizing antagonist microorganisms has been recognized as a type of biological control (BC), which could represent a viable and environmentally safe alternative to synthetic fungicides. Despite the ecological benefit that derives from the use of controllers and biological control agents (BCA) at a commercial level, their application and efficient use has been minimal at a global level.
By means of density functional theory (DFT) computations, we systematically explored the potential of the single-sided chemically functionalized graphene by various functional groups as the ...metal–free electrocatalyst for oxygen reduction reaction in alkaline media. Our computations revealed that the spin density due to the single-sided functionalization at 12.5% ratio enhances O2 adsorption, and the O2 adsorption energies well correlate with the magnetic moments of C8R graphenes. C8F and C8(OCH3) graphenes with moderate magnetic moments exhibit appropriate chemical reactivity towards O2 activation. The following ORR elemental steps prefer to proceed through a 4e− associative pathway, rather than the dissociative and 2e associative pathway. Both C8F and C8(OCH3) graphenes are promising ORR catalysts, and C8(OCH3) graphene is more efficient due to its lower overpotential. The present work provides an effective way to tune the catalytic performance of graphene for ORR by introducing a suitable spin density using its covalent functionalization.
PDF
