Xi Wang

A novel Ni3N/graphene nanocomposite as supercapacitor electrode material with high capacitance and energy density

A novel Ni3N/graphene nanocomposite of small Ni3N nanoparticles anchoring on the reduced graphene oxide nanosheets has been successfully synthesized. Due to the quite small size of Ni3N nanocrystals, the surface for faradic redox reaction of pseudocapacitive materials dramatically increases. The main issue of the volume change obstructing the pseudo-supercapacitor performance is concurrently resolved by the tight attachment of Ni3N nanoparticles with flexible texture. Importantly, the two-step oxidation/reduction reaction between Ni(I) and Ni(III) endows this nanocomposite with large capacitance by providing more faradic charge. The kind of electrode material behaves excellently both in three-electrode and asymmetric supercapacitors. The biggest specific capacitance reaches to 2087.5 F g(-1) (at 1 A g(-1)), and its asymmetric supercapacitor cell with ethylene glycol modified RGO as negative electrode has a high energy density (50.5 W h kg(-1) at 800 W kg(-1)). The cell capacitance retention exceeds 80% after 5000 cycles at different high current densities, showing its promising prospects for high-energy supercapacitors.

“Protrusions” or “holes” in graphene: which is the better choice for sodium ion storage?

The main challenge associated with sodium-ion battery (SIB) anodes is a search for novel candidate materials with high capacity and excellent rate capability. The most commonly used and effective route for graphene-based anode design is the introduction of in-plane “hole” defects via nitrogen-doping; this creates a spacious reservoir for storing more energy. Inspired by mountains in nature, herein, we propose another way – the introduction of blistering in graphene instead of making “holes”; this facilitates adsorbing/inserting more Na+ ions. In order to properly answer the key question: ““protrusions” or “holes” in graphene, which is better for sodium ion storage?”, two types of anode materials with a similar doping level were designed: a phosphorus-doped graphene (GP, with protrusions) and a nitrogen-doped graphene (GN, with holes). As compared with GN, the GP anode perfectly satisfies all the desired criteria: it reveals an ultrahigh capacity (374 mA h g−1 after 120 cycles at 25 mA g−1) comparable to the best graphite anodes in a standard Li-ion battery (∼372 mA h g−1), and exhibits an excellent rate capability (210 mA h g−1 at 500 mA g−1). In situ transmission electron microscopy (TEM) experiments and density functional theory (DFT) calculations were utilized to uncover the origin of the enhanced electrochemical activity of “protrusions” compared to “holes” in SIBs, down to the atomic scale. The introduction of protrusions through P-doping into graphene is envisaged to be a novel effective way to enhance the capacity and rate performance of SIBs.

Improved Li+ Storage through Homogeneous N-Doping within Highly Branched Tubular Graphitic Foam

A novel carbon structure, highly branched homogeneous-N-doped graphitic (BNG) tubular foam, is designed via a novel N, N-dimethylformamide (DMF)-mediated chemical vapor deposition method. More structural defects are found at the branched portions as compared with the flat tube domains providing abundant active sites and spacious reservoirs for Li+ storage. An individual BNG branch nanobattery is constructed and tested using in situ transmission electron microscopy and the lithiation process is directly visualized in real time.

In situ electrochemical formation of core–shell nickel–iron disulfide and oxyhydroxide heterostructured catalysts for a stable oxygen evolution reaction and the associated mechanisms

For electrochemical production of H2 fuels from water splitting, the development of efficient and economic catalysts for the oxygen evolution reaction (OER) is still a challenging issue. This is because an OER process usually involves multiple electron-transfer and reaction steps; these result in large overpotentials and significant energy loss. Thus, a smart design of highly efficient, stable and cheap OER electrocatalysts is important for the improvement of energy conversion efficiency and reduction of water splitting procedure cost. In this work, we find that a thin crystalline oxyhydroxide layer has been in situ electrochemically formed on the surfaces of conductive nickel–iron disulfide nanostructures; such a heterostructure takes advantage of highly catalytically active oxyhydroxide surfaces and excellent conductivity of the interior disulfide phase. This results in a very low overpotential of 230 mV at a current density of 10 mA cm−2, which is among the best OER catalysts in alkaline electrolyte ever reported. The crystalline oxyhydroxide layer can effectively prevent the disulfide core from further oxidation, maintains the core–shell structure of the catalyst and is considered to be critical for stable and efficient OER performances.

In Situ Electrochemistry of Rechargeable Battery Materials: Status Report and Perspectives

The development of rechargeable batteries with high performance is considered to be a feasible way to satisfy the increasing needs of electric vehicles and portable devices. It is of vital importance to design electrodes with high electrochemical performance and to understand the nature of the electrode/electrolyte interfaces during battery operation, which allows a direct observation of the complicated chemical and physical processes within the electrodes and electrolyte, and thus provides real-time information for further design and optimization of the battery performance. Here, the recent progress in in situ techniques employed for the investigations of material structural evolutions is described, including characterization using neutrons, X-ray diffraction, and nuclear magnetic resonance. In situ techniques utilized for in-depth uncovering the electrode/electrolyte phase/interface change mechanisms are then highlighted, including transmission electron microscopy, atomic force microscopy, X-ray spectroscopy, and Raman spectroscopy. The real-time monitoring of lithium dendrite growth and in situ detection of gas evolution during charge/discharge processes are also discussed. Finally, the major challenges and opportunities of in situ characterization techniques are outlined toward new developments of rechargeable batteries, including innovation in the design of compatible in situ cells, applications of dynamic analysis, and in situ electrochemistry under multi-stimuli. A clear and in-depth understanding of in situ technique applications and the mechanisms of structural evolutions, surface/interface changes, and gas generations within rechargeable batteries is given here.

Tuning of the Optical, Electronic, and Magnetic Properties of Boron Nitride Nanosheets with Oxygen Doping and Functionalization

Engineering of the optical, electronic, and magnetic properties of hexagonal boron nitride (h-BN) nanomaterials via oxygen doping and functionalization has been envisaged in theory. However, it is still unclear as to what extent these properties can be altered using such methodology because of the lack of significant experimental progress and systematic theoretical investigations. Therefore, here, comprehensive theoretical predictions verified by solid experimental confirmations are provided, which unambiguously answer this long-standing question. Narrowing of the optical bandgap in h-BN nanosheets (from ≈5.5 eV down to 2.1 eV) and the appearance of paramagnetism and photoluminescence (of both Stokes and anti-Stokes types) in them after oxygen doping and functionalization are discussed. These results are highly valuable for further advances in semiconducting nanoscale electronics, optoelectronics, and spintronics.

Crystalline Cu-silicide stabilizes the performance of a high capacity Si-based Li-ion battery anode

Metal-silicides have demonstrated bright prospects as advanced anodes for lithium-ion batteries (LIBs). However, their roles in volume change accommodations are still unclear to us. Here, we design and fabricate a nanoporous Si/Cu0.83Si0.17/Cu composite, supported with a highly crystalline Cu-silicide/Cu rigid framework, which demonstrates a high reversible capacity of 820.4 mA h g−1 after 500 cycles at a current density of 3 A g−1. According to the in situ TEM, there was no obvious structural damage and electrode pulverization during the initial lithiation, and a highly crystalline LiCuSi phase was observed. Furthermore, the conversion of the Cu0.83Si0.17/LiCuSi couple during repeated cycles is highly reversible, and the structural integrity could be well maintained. These results demonstrate that the highly crystalline Cu-silicide together with the nanoporous structure contributes to the ultrastable cycle performance and the Cu-silicide/Cu rigid framework supported the superior rate performance. The present work points out a facile but effective strategy for the engineering of alloy type anodes with superior cycle and rate properties for next generation LIBs.

Construction of Polarized Carbon–Nickel Catalytic Surfaces for Potent, Durable, and Economic Hydrogen Evolution Reactions

Electrocatalytic hydrogen evolution reaction (HER) in alkaline solution is hindered by its sluggish kinetics toward water dissociation. Nickel-based catalysts, as low-cost and effective candidates, show great potentials to replace platinum (Pt)-based materials in the alkaline media. The main challenge regarding this type of catalysts is their relatively poor durability. In this work, we conceive and construct a charge-polarized carbon layer derived from carbon quantum dots (CQDs) on Ni3N nanostructure (Ni3N@CQDs) surfaces, which simultaneously exhibit durable and enhanced catalytic activity. The Ni3N@CQDs shows an overpotential of 69 mV at a current density of 10 mA cm-2 in a 1 M KOH aqueous solution, lower than that of Pt electrode (116 mV) at the same conditions. Density functional theory (DFT) simulations reveal that Ni3N and interfacial oxygen polarize charge distributions between originally equal C-C bonds in CQDs. The partially negatively charged C sites become effective catalytic centers for the key water dissociation step via the formation of new C-H bond (Volmer step) and thus boost the HER activity. Furthermore, the coated carbon is also found to protect interior Ni3N from oxidization/hydroxylation and therefore guarantees its durability. This work provides a practical design of robust and durable HER electrocatalysts based on nonprecious metals.

Recent Advances in Designing High‐Capacity Anode Nanomaterials for Li‐Ion Batteries and Their Atomic‐Scale Storage Mechanism Studies

Abstract Lithium‐ion batteries (LIBs) have been widely applied in portable electronics (laptops, mobile phones, etc.) as one of the most popular energy storage devices. Currently, much effort has been devoted to exploring alternative high‐capacity anode materials and thus potentially constructing high‐performance LIBs with higher energy/power density. Here, high‐capacity anode nanomaterials based on the diverse types of mechanisms, intercalation/deintercalation mechanism, alloying/dealloying reactions, conversion reaction, and Li metal reaction, are reviewed. Moreover, recent studies in atomic‐scale storage mechanism by utilizing advanced microscopic techniques, such as in situ high‐resolution transmission electron microscopy and other techniques (e.g., spherical aberration‐corrected scanning transmission electron microscopy, cryoelectron microscopy, and 3D imaging techniques), are highlighted. With the in‐depth understanding on the atomic‐scale ion storage/release mechanisms, more guidance is given to researchers for further design and optimization of anode nanomaterials. Finally, some possible challenges and promising future directions for enhancing LIBs capacity are provided along with the authors personal viewpoints in this research field.

Biofabrication Strategy for Functional Fabrics

Functional fabrics with various unique properties are necessary for making fantastic superior costumes just like a superhero suit in Marvel Comics, which are not only dreams of boys but also emerging textiles to facilitate human life. On the basis of the inspiration of a phenomenon in an extracurricular experiment for kids, we develop a biofabrication strategy to endow silk textiles with various unique physical and chemical properties of functional nanomaterials, where the functional textiles are weaved using silk spun by silkworms that are fed with functional nanomaterials. To confirm the feasibility of this strategy, a photoluminescent plain weave was prepared successfully via feeding biocompatible luminescent nanoparticles to Bombyx mori silkworms. As the functional nanomaterials are enclosed in the silkfibers, the given special properties will be permanent for further application. Considering the wondrous diversity of properties that a variety of nanomaterials possesses may be given to silk fabric, it is promising to see various miraculous costumes in the coming future.