Xiangju Xu

A Lightweight TiO2/Graphene Interlayer, Applied as a Highly Effective Polysulfide Absorbent for Fast, Long‐Life Lithium–Sulfur Batteries

DOI: 10.1002/adma.201405637 using microporous carbon paper and achieved signifi cant improvements not only in the use of the active material but also in the capacity retention. [ 12 ] More recently, various free-standing carbon interlayers including carbonized paper, a carbonized eggshell membrane, and an acetylene black mesh have been developed for the interception of migrating PS ions. [ 13–15 ] Investigating different categories of carbon interlayers has become a major avenue of current research into the insertion of interlayers. Meanwhile, non-carbon interlayers also appeared on stage. A typical example is that the Li + selective permselective membrane based on a coating layer of Nafi on blocks the diffusion of PS anions across the membrane to the Li anode, which greatly suppresses the shuttling of PS. [ 16 ] Since the diffusion of PS was localized on the cathode side, the cycling stability of the Li–S battery can be dramatically improved. Although these carbon and non-carbon interlayers have shown that it is possible to suppress the diffusion of PS and to improve the cycle-ability, some crucial issues remain to be resolved: i) As for these carbon and non-carbon interlayers, the complexity of the processes required for the synthesis of unique interlayers hinders their large-scale application, furthermore, the unsatisfactory thickness/weight of the applied interlayer may lead to a sharp decrease in the overall energy density, which may offset the gains in cell performance; ii) when the carbon interlayer acts only as a physical barrier, its nonpolar nature leads to weak interaction with polar PS anions, greatly reducing their ability to bind and confi ne these species during cycling. Moreover, the Li + ion transfer may be impeded by the physical barrier; iii) with regard to the non-carbon interlayer, a lower initial discharge capacity compared to the counterpart cathode was arisen likely due to increasing the resistance to some extent. To address shuttling of PS issues, the adjustment of the interlayer components may be a desirable strategy; in theory, an ideal interlayer should be able to selectively control the shuttling of PS anions via strong chemical interactions between them, while not disturbing the Li + ion transfer. Developing a lightweight and chemically selective interlayer carbon is therefore seems to be urgent. Previous reports have demonstrated the successful coupling of mesoporous TiO 2 additives to a C–S composite to improve the cycle life and the capacity retention. [ 6,17 ] It was shown recently that Li–S batteries could achieve 1000 cycles when the sulfur was coated with TiO 2 to create yolk–shell structures. [ 18 ] These results indicated that the mesoporous TiO 2 used in the coating layers promoted the interaction between TiO 2 and S, which was believed to be an electrostatic attraction (S–Ti–O) [ 6,19 ] that improved the surface adsorption of PS on the TiO 2 . Inspired by these results, and after comprehensively considering the three The development of advanced electrode materials with high energy/power density for energy storage is critical for a sustainable society. [ 1,2 ] Among existing materials, lithium–sulfur (Li–S) batteries show great potential for next-generation electrical energy storage applications. Sulfur cathodes, as well as being cost-effective and environmental friendly, provide a high theoretical capacity of 1675 mA h g −1 , a value that is an order of magnitude greater than typical values for conventional lithiated cathodes. [ 3 ] Despite the great promise of Li–S batteries, two main technical challenges must be addressed before they can fi nd practical use. First, the intrinsically poor electronic conductivity of sulfur leads to low use of the active material. Second, the high solubility of the polysulfi de’s (PS) reaction intermediaries (Li 2 S x , 4 < x < 8), and the action of their notorious “shuttle” mechanism in organic electrolytes, produce a rapid decline in the capacity, and a short cycle life. [ 4 ] To facilitate the development of the Li–S system, it is therefore crucial to improve the conductivity of the sulfur cathode and maintain/ reuse the soluble PS within the cathode structure. [ 5 ]

Metal-free selenium doped carbon nanotube/graphene networks as a synergistically improved cathode catalyst for oxygen reduction reaction

The ongoing search for new non-precious-metal catalysts (NPMCs) with excellent electrocatalytic performance to replace Pt-based catalysts has been viewed as an important strategy to promote the development of fuel cells. Recent studies have proven that carbon materials doped with atoms which have a relatively small atomic size (e.g. N, B, P or S), have also shown pronounced catalytic activity. Herein, we demonstrate the successful fabrication of CNT/graphene doped with Se atoms, which has a relatively large atomic size, by a simple, economical, and scalable approach. The electrocatalytic performance of the resulting Se-doped CNT-graphene catalyst exhibits excellent catalytic activity, long-term stability, and a high methanol tolerance compared to commercial Pt/C catalysts. Our results confirmed that combining CNTs with graphene is an effective strategy to synergistically improve ORR activity. More importantly, it is also suggested that the development of graphite materials doped with Se or other heteroatoms of large size will open up a new route to obtain ideal NPMCs with realistic value for fuel cell applications.

Facile synthesis of Cu2ZnSnS4 nanocrystals

A facile, greener and inexpensive method was developed to synthesize high quality quarternary Cu2ZnSnS4 (CZTS) nanocrystals at temperature lower than 220 °C, in which Cu2ZnSn(S2CNEt2)10, oleylamine and oleic acid were used as the precursor, activation agent and capping agent, respectively.

A lightweight multifunctional interlayer of sulfur–nitrogen dual-doped graphene for ultrafast, long-life lithium–sulfur batteries

Lithium–sulfur batteries are a promising candidate for next-generation battery systems owing to their low cost and high theoretical capacity and energy density. However, the notorious shuttle effect of the intermediate polysulfides as well as low conductivity of sulfur greatly limits their practical applications. Here, we introduce a new design that uses a porous-CNT/S cathode (PCNT–S) coupled with a lightweight multifunctional porous sulfur–nitrogen dual-doped graphene (SNGE) interlayer. It is confirmed that the introduced SNGE has outstanding conductivity, high ability to trap polysulfides, ability to modulate Li2S2/Li2S growth, and the functionality to protect separator integrity. With such rich functionalities, the SNGE interlayer enables the PCNT–S cathode to deliver a reversible specific capacity of ∼1460 mA h g−1 at 0.25C and a much higher rate performance, up to 40C, with a capacity retention of 130 mA h g−1. Critically, these cathodes exhibited ultrahigh cyclability when cycled at 8C for 1000 cycles, exhibiting a capacity degradation rate of 0.01% per cycle. To the best of our knowledge, such a low capacity degradation rate beyond 5C in the cathodes of advanced Li–S batteries has been reported only rarely. These results impressively revealed the outstanding high-power output performance of the Li–S batteries.

Self-catalytic growth of unmodified gold nanoparticles as conductive bridges mediated gap-electrical signal transduction for DNA hybridization detection.

A simple and sensitive gap-electrical biosensor based on self-catalytic growth of unmodified gold nanoparticles (AuNPs) as conductive bridges has been developed for amplifying DNA hybridization events. In this strategy, the signal amplification degree of such conductive bridges is closely related to the variation of the glucose oxidase (GOx)-like catalytic activity of AuNPs upon interaction with single- and double-stranded DNA (ssDNA and dsDNA), respectively. In the presence of target DNA, the obtained dsDNA product cannot adsorb onto the surface of AuNPs due to electrostatic interaction, which makes the unmodified AuNPs exhibit excellent GOx-like catalytic activity. Such catalytic activity can enlarge the diameters of AuNPs in the glucose and HAuCl4 solution and result in a connection between most of the AuNPs and a conductive gold film formation with a dramatically increased conductance. For the control sample, the catalytic activity sites of AuNPs are fully blocked by ssDNA due to the noncovalent interaction between nucleotide bases and AuNPs. Thus, the growth of the assembled AuNPs will not happen and the conductance between microelectrodes will be not changed. Under the optimal experimental conditions, the developed strategy exhibited a sensitive response to target DNA with a high signal-to-noise ratio. Moreover, this strategy was also demonstrated to provide excellent differentiation ability for single-nucleotide polymorphism. Such performances indicated the great potential of this label-free electrical strategy for clinical diagnostics and genetic analysis under real biological sample separation.

Ag2S-catalyzed growth of quaternary AgInZn7S9 semiconductor nanowires in solution

A facile and inexpensive solution-based synthesis of quaternary AgInZn7S9 nanowires was developed. Structural and compositional characterizations were carried out by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) analysis, and powder X-ray diffraction (XRD). The as-synthesized AgInZn7S9 nanowires have high quality and moderate band structure. The growth mechanism is also investigated. It is confirmed that Ag2S nanoparticles derived from the decomposition of precursor Ag(dedc) act as a catalyst during the growth of quaternary nanowires. The catalysts in this process were found to be in a quasi-liquid state and only the surface region of the catalysts melted, which is different from the liquid state in the typical Solution–Liquid–Solid growth process.

Controllable synthesis of highly uniform flower-like hierarchical carbon nanospheres and their application in high performance lithium–sulfur batteries

Elemental sulfur cathodes for lithium/sulfur batteries are receiving intense interest owing to their high theoretical capacity and energy density. However, they still suffer from severe capacity fading and moderate rate capability. Herein, we provide rational design and controllable fabrication of highly uniform flower-like hierarchical carbon nanospheres (FCNS) for sulfur accommodation for lithium/sulfur battery cathodes. The as-prepared three dimension FCNS with a size of around 200 nm seem to be assembled by petal-like carbon nanosheets with a thickness of about 4 nm, forming many mesoporous channels, which lead to their high surface area and large pore volume. With such a tailor-made structure, FCNS/sulfur composite cathodes with high sulfur-loading (81 wt%) deliver high specific capacity, long cycling life and excellent rate capability. Particularly, N-doped flower-like carbon nanospheres (NFCNS) with higher surface area (1223 m2 g−1) and larger pore volume (2.33 cm3 g−1) are also fabricated by treating with NH3 and used to host sulfur in lithium–sulfur battery cathodes, exhibiting more excellent rate capability (829 mA h g−1 at 5C) and cycling stability with a decay of 0.03% per cycle over 200 cycles at 1C. Even though the area density is improved to 2.5 mg sulfur per cm2, the battery still has a decay of 0.056% per cycle over 200 cycles.

Controlling the Diameter of Single-Walled Carbon Nanotubes by Improving the Dispersion of the Uniform Catalyst Nanoparticles on Substrate

To have uniform nanoparticles individually dispersed on substrate before single-walled carbon nanotubes (SWNTs) growth at high temperature is the key for controlling the diameter of the SWNTs. In this letter, a facile approach to control the diameter and distribution of the SWNTs by improving the dispersion of the uniform Fe/Mo nanoparticles on silicon wafers with silica layer chemically modified by 1,1,1,3,3,3-hexamethyldisilazane under different conditions is reported. It is found that the dispersion of the catalyst nanoparticles on Si wafer surface can be improved greatly from hydrophilic to hydrophobic, and the diameter and distribution of the SWNTs depend strongly on the dispersion of the catalyst on the substrate surface. Well dispersion of the catalyst results in relatively smaller diameter and narrower distribution of the SWNTs due to the decrease of aggregation and enhancement of dispersion of the catalyst nanoparticles before growth. It is also found that the diameter of the superlong aligned SWNTs is smaller with more narrow distribution than that of random nanotubes.

Growth of Single-Walled Carbon Nanotubes from Well-Defined POSS Nanoclusters Structure

High-quality single-walled carbon nanotubes (SWNTs) with narrow diameter distribution can be generated from well-defined Si8O12 nanoclusters structure which form from thermal decomposition of chemically modified polyhedral oligomeric silsesquioxane (POSS). The nanosized SixOy particles were proved to be responsible for the SWNT growth and believed to be the reason for the narrow diameter distribution of the as-grown SWNTs. This could be extended to other POSS. The SWNTs grown from the nanosized SixOy particles were found to be semiconducting enriched SWNTs (s-SWNTs). A facile patterning technology, direct photolithography, was developed for generating SWNT pattern, which is compatible to industrial-level fabrication of SWNTs pattern for device applications. The metal-free growth together with preferential growth of s-SWNTs and patterning in large scale from the structure-defined silicon oxide nanoclusters not only represent a big step toward the control growth of SWNTs and fabrication of devices for appli...