Polymorphic Cobalt Sulfide-Embedded Graphene Foam with Ultralong Cycling and Ultrafast Rate Capability for Potassium-Ion Batteries

Potassium-ion batteries (KIBs) attract growing attention due to their low price and abundant resources. However, the main drawback is the large-sized potassium ions, which results in a lack of superior capacity and desirable stable materials. We herein propose the Co9S8/GF nanocomposite synthesized by a solvothermal route followed by heat treatment under the reduction atmosphere with the CoS/GF nanocomposite as the control group. The as-synthesized Co9S8 has a typical morphology of vertically arranged uniform nanosheet arrays. The Co9S8/GF nanocomposite electrode delivers a capacity of 345.65 mAh·g–1 after 600 cycles at 500 mA·g–1 and even 343.06 mAh·g–1 after 1360 cycles at 5000 mA·g–1 in KIBs. Besides, the discharge capacity can reach 461.05 mAh·g–1 after the current increases to 5000 mA·g–1 and a reversible capacity of 578.40 mAh·g–1 when the current density recovers to 250 mA·g–1 again. At last, the charge storage behaviors are mainly discussed, and the unique structure can suffer the volumetric change, especially at high current density, which opens up a novel and effective way to build the embedded porous structure for the next-generation KIB technology

Plasmon-Modulated Photoluminescence of Individual Gold Nanostructures

In this work, we performed a systematic study on the photoluminescence and scattering spectra of individual gold nanostructures that were lithographically defined. We identify the role of plasmons in photoluminescence as modulating the energy transfer between excited electrons and emitted photons. By comparing photoluminescence spectra with scattering spectra, we observed that the photoluminescence of individual gold nanostructures showed the same dependencies on shape, size, and plasmon coupling as the particle plasmon resonances. Our results provide conclusive evidence that the photoluminescence in gold nanostructures indeed occurs <i>via</i> radiative damping of plasmon resonances driven by excited electrons in the metal itself. Moreover, we provide new insight on the underlying mechanism based on our analysis of a reproducible blue shift of the photoluminescence peak (relative to the scattering peak) and observation of an incomplete depolarization of the photoluminescence

Plasmon-Modulated Photoluminescence of Single Gold Nanobeams

In this work, we investigate the modulation of the photoluminescence (PL) of a single Au nanobeam (NB) by the surface plasmons of a Ag nanowire (NW) and the gap plasmons between the two nanostructures. By changing the polarization of the laser that excites the nanostructure and controlling the separation distance <i>d</i> between the two nanostructures, we found that the transverse surface plasmon resonance of the Ag NW enhanced the PL (at 520 nm) of the Au NB with a maximum effect at <i>d</i> = 7 nm. The PL enhancement (at 520 nm) was quenched and a new PL peak was observed at a longer wavelength for <i>d</i> < 7 nm. The PL quenching effect could be understood by the quadrupole-like plasmonic resonance between the Ag NW and the Au NB and be qualitatively explained by the mode dispersion as a function of <i>d</i> obtained using the transfer matrix transmittance calculation. FDTD simulations show that the new PL peak at a longer wavelength is caused by the waveguide-mode gap plasmons between the Au NB and the Ag NW

Aqueous Rechargeable Alkaline Co_<i>x</i>Ni_2–<i>x</i>S₂/TiO₂ Battery

An electrochemical energy storage system with high energy density, stringent safety, and reliability is highly desirable for next-generation energy storage devices. Here an aqueous rechargeable alkaline Co_<i>x</i>Ni_2–<i>x</i>S₂ // TiO₂ battery system is designed by integrating two reversible electrode processes associated with OH^– insertion/extraction in the cathode part and Li ion insertion/extraction in the anode part, respectively. The prototype Co_<i>x</i>Ni_2–<i>x</i>S₂ // TiO₂ battery is able to deliver high energy/power densities of 83.7 Wh/kg at 609 W/kg (based on the total mass of active materials) and good cycling stabilities (capacity retention 75.2% after 1000 charge/discharge cycles). A maximum volumetric energy density of 21 Wh/l (based on the whole packaged cell) has been achieved, which is comparable to that of a thin-film battery and better than that of typical commercial supercapacitors, benefiting from the unique battery and hierarchical electrode design. This hybrid system would enrich the existing aqueous rechargeable LIB chemistry and be a promising battery technology for large-scale energy storage

Refined Sulfur Nanoparticles Immobilized in Metal–Organic Polyhedron as Stable Cathodes for Li–S Battery

The lithium–sulfur (Li–S) battery presents a promising rechargeable energy storage technology for the increasing energy demand in a worldwide range. However, current main challenges in Li–S battery are structural degradation and instability of the solid-electrolyte interphase caused by the dissolution of polysulfides during cycling, resulting in the corrosion and loss of active materials. Herein, we developed novel hybrids by employing metal–organic polyhedron (MOP) encapsulated PVP-functionalized sulfur nanoparticles (S@MOP), where the active sulfur component was efficiently encapsulated within the core of MOP and PVP as a surfactant was helpful to stabilize the sulfur nanoparticles and control the size and shape of corresponding hybrids during their syntheses. The amount of sulfur embedded into MOP could be controlled according to requirements. By using the S@MOP hybrids as cathodes, an obvious enhancement in the performance of Li–S battery was achieved, including high specific capacity with good cycling stability. The MOP encapsulation could enhance the utilization efficiency of sulfur. Importantly, the structure of the S@MOP hybrids was very stable, and they could last for almost 1000 cycles as cathodes in Li–S battery. Such high performance has rarely been obtained using metal–organic framework systems. The present approach opens up a promising route for further applications of MOP as host materials in electrochemical and energy storage fields

Anomalous Shift Behaviors in the Photoluminescence of Dolmen-Like Plasmonic Nanostructures

Localized surface plasmon resonance (LSPR) on metallic nanostructures is able to enhance photoluminescence (PL) emission significantly. However, the mechanism for anomalous blue-shifted peak of PL emission from metallic nanostructures, relative to the corresponding scattering spectra, is still unclear so far. In this paper, we presented the detailed investigations on both the Lorentz-like PL profile with blue-shifted peak and Fano-like one with almost unshifted dip, as observed on dolmen-like metallic nanostructures. Such anomalous PL emission profile is the product of the density of plasmon states (DoPS) with Lorentz-/Fano-like profile and the population distribution of the relaxed collective free electrons during relaxation. To be more specific, the fast relaxation process of these collective free electrons contributes to the PL shifting characteristics of both Lorentz-like and Fano-like emission profiles. We believed that our results provide a general solid foundation and guidance for analyzing and manipulating the physical processes of the PL emission from various plasmonic nanostructures

A Flexible Alkaline Rechargeable Ni/Fe Battery Based on Graphene Foam/Carbon Nanotubes Hybrid Film

The development of portable and wearable electronics has promoted increasing demand for high-performance power sources with high energy/power density, low cost, lightweight, as well as ultrathin and flexible features. Here, a new type of flexible Ni/Fe cell is designed and fabricated by employing Ni­(OH)₂ nanosheets and porous Fe₂O₃ nanorods grown on lightweight graphene foam (GF)/carbon nanotubes (CNTs) hybrid films as electrodes. The assembled f-Ni/Fe cells are able to deliver high energy/power densities (100.7 Wh/kg at 287 W/kg and 70.9 Wh/kg at 1.4 kW/kg, based on the total mass of active materials) and outstanding cycling stabilities (retention 89.1% after 1000 charge/discharge cycles). Benefiting from the use of ultralight and thin GF/CNTs hybrid films as current collectors, our f-Ni/Fe cell can exhibit a volumetric energy density of 16.6 Wh/l (based on the total volume of full cell), which is comparable to that of thin film battery and better than that of typical commercial supercapacitors. Moreover, the f-Ni/Fe cells can retain the electrochemical performance with repeated bendings. These features endow our f-Ni/Fe cells a highly promising candidate for next generation flexible energy storage systems

Pseudocapacitive Na-Ion Storage Boosts High Rate and Areal Capacity of Self-Branched 2D Layered Metal Chalcogenide Nanoarrays

The abundant reserve and low cost of sodium have provoked tremendous evolution of Na-ion batteries (SIBs) in the past few years, but their performances are still limited by either the specific capacity or rate capability. Attempts to pursue high rate ability with maintained high capacity in a single electrode remains even more challenging. Here, an elaborate self-branched 2D SnS₂ (B-SnS₂) nanoarray electrode is designed by a facile hot bath method for Na storage. This interesting electrode exhibits areal reversible capacity of <i>ca</i>. 3.7 mAh cm^–2 (900 mAh g^–1) and rate capability of 1.6 mAh cm^–2 (400 mAh g^–1) at 40 mA cm^–2 (10 A g^–1). Improved extrinsic pseudocapacitive contribution is demonstrated as the origin of fast kinetics of an alloying-based SnS₂ electrode. Sodiation dynamics analysis based on first-principles calculations, <i>ex-situ</i> HRTEM, <i>in situ</i> impedance, and <i>in situ</i> Raman technologies verify the S-edge effect on the fast Na⁺ migration and reversible and sensitive structure evolution during high-rate charge/discharge. The excellent alloying-based pseudocapacitance and unsaturated edge effect enabled by self-branched surface nanoengineering could be a promising strategy for promoting development of SIBs with both high capacity and high rate response

Hydrogen-Bonding Evolution during the Polymorphic Transformations in CH₃NH₃PbBr₃: Experiment and Theory

Hydrogen bonding exists in all hybrid organic–inorganic lead halide perovskites MAPbX₃ (X = Cl, Br, or I). It has a strong influence on the structure, stability, and electronic and optical properties of this perovskite family. The hydrogen-bonding state between the H atoms of the methylammonium (MA) cation and the halide ions is resolved by combining <i>ab initio</i> calculations with temperature-dependent Raman scattering and powder X-ray diffraction measurements on MAPbBr₃ hybrid perovskites. When the compounds are cooled, the H-bonding in the NH₃ end of the MA group shows sequential changes while the H atoms in the CH₃ end form H bonds with only the Br ions in the orthorhombic phase, leading to a decrease in the degree of rotational freedom of MA and a narrowing for MA Raman modes. Hydrogen bonding drives the evolution of temperature-dependent rotations of the MA cation and the concomitant tilting of PbX₆ octahedra with the consequent dynamical change in the electronic band structures, from indirect bandgap to direct bandgap along with ∼60-fold PL emission enhancement upon cooling. We experimentally and theoretically reveal the evolution of hydrogen bonding during polymorphic transformations and how the different types of hydrogen bonding lead to specific optoelectronic properties and device applications of hybrid perovskites

Recyclable and Ultrafast Fabrication of Zinc Oxide Interface Layer Enabling Highly Reversible Dendrite-Free Zn Anode

The surface coating is effective in suppressing Zn dendrite and side reactions, while the existing processing methods employ complex procedures and expensive equipment. Here, we develop an I2-assisted processing method to in situ fabricate the ZnO interface layer on the Zn anode (denoted as IAZO). This strategy features the sustainability that the raw materials, I2, could be reused with a recovery ratio of 67.25% and rapid processing time that only takes 5 min. The IAZO anode achieves an extraordinary cycle life of over 3100 h and a high depth of discharge of 52%, much better than the original Zn anode (less than 220 h and 1.7%). Density functional theory calculations and COMSOL simulation reveal that the IAZO anode has a high binding energy with Zn2+, which contributes to the uniform distribution of the electric field and Zn2+ flux