Uniformly MXene-Grafted Eutectic Aluminum-Cerium Alloys as Flexible and Reversible Anode Materials for Rechargeable Aluminum-Ion Battery

Aluminum is an attractive anode material in aqueous multivalent-metal batteries for large-scale energy storage because of its high Earth abundance, low cost, high theoretic capacity, and safety. However, state-of-the-art aqueous aluminum-ion batteries based on aluminum anode persistently suffer from poor rechargeability and low coulombic efficiency due to irreversibility of aluminum stripping/plating and dendrite growth. Here eutectic aluminum-cerium alloys in situ grafted with uniform ultrathin MXene (MXene/E-Al₉₇Ce₃) as flexible, reversible, and dendrite-free anode materials for rechargeable aqueous aluminum-ion batteries is reported. As a result of the MXene serving as stable solid electrolyte interphase to inhibit side reactions and the lamella-nanostructured E-Al₉₇Ce₃ enabling directional Al stripping and deposition by making use of symbiotic α-Al metal and intermetallic Al₁₁Ce₃ lamellas, the MXene/E-Al₉₇Ce₃ hybrid electrodes exhibit reversible and dendrite-free Al stripping/plating with low voltage polarization of ± 54 mV for ≥1000 h in a low-oxygen-concentration aqueous aluminum trifluoromethanesulfonate (Al(OTF)₃) electrolyte. These superior electrochemical properties endow soft-package aluminum-ion batteries assembled with MXene/E-Al₉₇Ce₃ anode and Al_xMnO₂ cathode to have high initial discharge capacity of ≈360 mAh g⁻¹ at 1 A g⁻¹, and retain ≈85% after 500 cycles, along with the coulombic efficiency of as high as 99.5%.     

High-Performance Aqueous Zn2+/Al3+ Electrochromic Batteries based on Niobium Tungsten Oxides

Electrochromic energy storage devices (EESDs) are incorporating electrochromic and energy storage functions, which can visually display energy storage levels in real-time to promote the next generation of transparent battery development. However, their performances are still limited for practical applications. Herein, a self-powered EESD based on complex niobium tungsten oxide is designed using aqueous Zn²⁺ and hybrid Zn²⁺/Mⁿ⁺ (Mⁿ⁺ = Al³⁺, Mg²⁺, and K⁺) electrolytes. The results reveal that the use of Zn²⁺/Al³⁺ hybrid electrolyte achieves superior electrochromic performances including a short self-coloring time, high optical contrast, and excellent cyclic stability. Furthermore, it is also found that the self-coloring process is accompanied by a high discharged capacity of niobium tungsten oxide, with high optical modulation in the Zn²⁺/Al³⁺ hybrid electrolyte. The detailed mechanism on the performances of EESD using various electrolytes is systematically studied. This work provides a simple and effective strategy for an aqueous and self-powered EESD with high optical contrast and good cycle stability.     

Unconventional Aluminum Ion Intercalation/Deintercalation for Fast Switching and Highly Stable Electrochromism

Electrochromic devices have many important commercial applications ranging from electronic paper like displays, antiglare rear‐view mirrors in cars, to energy‐saving smart windows in buildings. Monovalent ions such as H⁺, Li⁺, and Na⁺ are widely used as insertion ions in electrochromic devices but have serious limitations such as instability, high‐cost, and hard handling. The utilization of trivalent ions as insertion ions has been largely overlooked probably because of the strong electrostatic interactions between ions and intercalation framework and the resulted difficulties of intercalation. It is demonstrated that the trivalent ion, Al³⁺, can be used as efficient insertion ion by using metal oxide hosts in nanostructured form, which brings the desired fast‐switch, high‐contrast, and high‐stability as well to electrochromic devices. Differing from the usual structure degradation by repeated guest intercalation/deintercalation, the Al³⁺ insertion introduces strong electrostatic forces, which on some degree stabilize the crystal structure and consequently yield much enhanced performances.     

A Dual-Mode Electrochromic Platform Integrating Zinc Anode-Based and Rocking-Chair Electrochromic Devices

The complementary electrochromic device, where the optical transmittance changes upon the flow of cations back and forth between anodic and cathodic electrodes, operates in a rocking-chair fashion if it can inherently self-discharge. Herein, the first demonstration of a dual-mode electrochromic platform having self-coloring and self-bleaching characteristics is reported, which is realized by sandwiching zinc metal within a newly-designed Prussian blue (PB)-WO₃ rocking-chair type electrochromic device. It is demonstrated that the redox potential differences between the zinc metal and the WO₃/PB electrodes endow the self-color-switching of these electrodes. By employing a hybrid electrolyte of Zn²⁺/K⁺, it is further shown that the colored PB-WO₃ rocking-chair device is capable of spontaneously bleaching when the anodic and cathodic electrodes are coupled. This dual-mode light-control strategy enables the electrochromic devices to exhibit four distinct optical states with the highest optical contrast of 72.6% and fast switching times (<5 s for the bleaching/coloration processes). Furthermore, the built-in voltage of the dual-mode electrochromic devices not only promotes energy efficiency, but also augments the bistability of the devices. It is envisioned that the broad implication of the present platform is in the development of self-powered smart windows, colorful displays, optoelectronic switches, and optical sensors.     

A Single-Composition Trichromatic White-Light-Emitting Phosphor Based on Sr<Subscript>8</Subscript>ZnY(PO<Subscript>4</Subscript>)<Subscript>7</Subscript> Coactivated with Ce<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript>, and Mn<Superscript>2+</Superscript>

Ce³⁺/Tb³⁺/Mn²⁺-codoped Sr₈ZnY(PO₄)₇ (SZYP) white-emitting phosphors have been synthesized via solid-state reaction technology. The overlapping spectra between the excitation bands of Mn²⁺ and Tb³⁺ ions and the emission band of Ce³⁺ suggest that Ce³⁺ → Mn²⁺ and Ce³⁺ → Tb³⁺ energy transfer occurs. The emission hues exhibited by Ce³⁺/Tb³⁺- and Ce³⁺/Mn²⁺-codoped phosphors could be modulated from bluish to greenish region and from bluish to reddish region by simply adjusting the relative content of Ce³⁺/Tb³⁺ and Ce³⁺/Mn²⁺, respectively. SZYP:Ce³⁺,Tb³⁺,Mn²⁺ samples exhibited three dominant bands at 410 nm, 545 nm, and 600 nm, attributable to electronic transitions of Ce³⁺, Tb³⁺, and Mn²⁺ ions, respectively. Thus, color-tunable emission was achieved by accurately modulating the concentrations of Ce³⁺, Tb³⁺, and Mn²⁺ ions. SZYP:0.05Ce³⁺,0.11Mn²⁺,0.11Tb³⁺ was found to be an ideal white-light-emitting phosphor with color coordinates of (0.34, 0.33) and correlated color temperature of about 5144.83 K. The results indicate that Ce³⁺/Tb³⁺/Mn²⁺ -tridoped SZYP phosphors are potential single-component white-emitting candidates for application in ultraviolet- and white-light-emitting diodes.     

Energy transfer of Ce3+ → Eu2+ in the CaGa2S4 compound

Photoluminescence of CaGa₂S₄:Eu²⁺, CaGa₂S₄:Ce³⁺, and CaGa₂S₄:(Eu²⁺, Ce³⁺) is shown to be caused by intracenter transitions of Eu²⁺ and Ce³⁺ ions. It is ascertained that an energy transfer with an efficiency of 0.43 takes place from Ce³⁺ to Eu²⁺.     

Studying the formation of nanoporous and nanotubular titanium layers by electrochemical impedance spectroscopy

Nanoporous and nanotubular titanium layers have been obtained via electrolytic etching in a mixed organic-inorganic electrolyte. The formation of layers has been studied in situ by electrochemical impedance spectroscopy. It has been shown that the impedance of an electrochemical cell is governed by the impedance of the contact between the electrolyte and titanium at the bottom of nanoporous and nanotubular layers almost throughout the entire process except the initial period. It has been revealed that the electrical resistance of the space charge region in a titanium layer is higher than the charge transfer resistance at the electrolyte/TiO _x interface. This indicates that the rate of the growth of porous and nanotubular layers obtained via etching in an organic-inorganic electrolyte is limited by the transfer of titanium and oxygen ions through an oxide layer instead of the diffusion of ions in the electrolyte.     

Ultralow-Salt-Concentration Electrolyte for High-Voltage Aqueous Zn Metal Batteries

Aqueous Zn metal batteries are regarded as a promising pathway for large-scale energy storage systems due to their green, low-cost, and intrinsically safe characteristics. However, they have long been suffered from narrow voltage windows and severe parasitic reactions (e.g., hydrogen evolution, corrosion, etc.), which hinder their further development. The above challenges are essentially related to the existence of hydrated ions (i.e., Zn(H₂O)_x²⁺ and SO₄²⁻·(H₂O)_x), which are highly reactive species. Herein, a counterintuitive ultralow-salt-concentration electrolyte strategy to solve the aforementioned problems by decreasing Zn salt concentration to reduce active hydrated ions is presented, so as to minimize water-induced side reactions and thus anomalously enlarge the electrolyte splitting voltage window. Additionally, the gap between the charge and discharge medium voltages of full cells is also narrowed due to the reduced polarization in the ultralow-salt-concentration electrolyte. By adopting this strategy, the Zn-Fe₄[Fe(CN)₆]₃ full cell stably works at a high-voltage of 1.40–2.30 V with a high cathode loading of ≈7 mg cm⁻² and the Zn-polyaniline full cell can stably work at 0.50–1.50 V with a high cathode loading of ≈11 mg cm⁻².     

A Bottom‐Up Approach to Build 3D Architectures from Nanosheets for Superior Lithium Storage

Two‐dimensional (2D) atomic layers such as graphene, and metal chalcogenides have recently attracted tremendous attention due to their unique properties and potential applications. Unfortunately, in most cases, the free‐standing nanosheets easily re‐stack due to their van der Waals forces, and lose the advantages of their separated atomic layer state. Here, a bottom‐up approach is developed to build three‐dimensional (3D) architectures by 2D nanosheets such as MoS₂ and graphene oxide nanosheets as building blocks, the thin nature of which can be well retained. After simply chemical reduction, the resulting 3D MoS₂‐graphene architectures possess high surface area, porous structure, thin walls and high electrical conductivity. Such unique features are favorable for the rapid diffusions of both lithium ions and electrons during lithium storage. As a consequence, MoS₂‐graphene electrodes exhibit high reversible capacity of ≈1200 mAh g^?1, with very good cycling performance. Moreover, such a simple and low‐cost assembly protocol can provide a new pathway for the large‐scale production of various functional 3D architectures for energy storage and conversions.     

Copper‐Based Nanostructured Coatings on Natural Cellulose: Nanocomposites Exhibiting Rapid and Efficient Inhibition of a Multi‐Drug Resistant Wound Pathogen,A. baumannii,and Mammalian Cell Biocompatibility In Vitro

This paper describes a layer‐by‐layer (LBL) electrostatic self‐assembly process for fabricating highly efficient antimicrobial nanocoatings on a natural cellulose substrate. The composite materials comprise a chemically modified cotton substrate and a layer of sub‐5 nm copper‐based nanoparticles. The LBL process involves a chemical preconditioning step to impart high negative surface charge on the cotton substrate for chelation controlled binding of cupric ions (Cu²⁺), followed by chemical reduction to yield nanostructured coatings on cotton fibers. These model wound dressings exhibit rapid and efficient killing of a multidrug resistant bacterial wound pathogen, A. baumannii, where an 8‐log reduction in bacterial growth can be achieved in as little as 10 min of contact. Comparative silver‐based nanocoated wound dressings–a more conventional antimicrobial composite material–exhibit much lower antimicrobial efficiencies; a 5‐log reduction in A. baumannii growth is possible after 24 h exposure times to silver nanoparticle‐coated cotton substrates. The copper nanoparticle–cotton composites described herein also resist leaching of copper species in the presence of buffer, and exhibit an order of magnitude higher killing efficiency using 20 times less total metal when compared to tests using soluble Cu²⁺. Together these data suggest that copper‐based nanoparticle‐coated cotton materials have facile antimicrobial properties in the presence of A. baumannii through a process that may be associated with contact killing, and not simply due to enhanced release of metal ion. The biocompatibility of these copper‐cotton composites toward embryonic fibroblast stem cells in vitro suggests their potential as a new paradigm in metal‐based wound care and combating pathogenic bacterial infections.     

3D Micromolding of Arrayed Waveguide Gratings on Upconversion Luminescent Layers for Flexible Transparent Displays without Mirrors,Electrodes, and Electric Circuits

A new technique for the fabrication of arrayed waveguide gratings on upconversion luminescent layers for flexible transparent displays is reported. Ho³⁺‐ and Yb³⁺‐codoped NaYF₄ nanoparticles are synthesized by hydrothermal techniques. Transparent films consisting of two transparent polymers on the NaYF₄ nanoparticle films exhibit mechanical flexibility and high transparence in visible region. Patterned NaYF₄ nanoparticle films are fabricated by calcination‐free micromolding in capillaries. Arrayed waveguide gratings consisting of the two transparent polymers are formed on the patterned NaYF₄ nanoparticle films by micromolding in capillaries. Green and red luminescence is observed from the upconversion luminescent layers of the NaYF₄ nanoparticle films in the arrayed waveguide gratings under excitation at 980 nm laser light. Arrayed waveguide gratings on the upconversion luminescent layers are fabricated with Er³⁺‐doped NaYF₄ nanoparticles which can convert two photons at 850 and 1500 nm into single photon at 550 nm. These results demonstrate that flexible transparent displays can be fabricated by constructing arrayed waveguide gratings on upconversion luminescent layers, which can operate in nonprojection mode without mirrors, transparent electrodes, and electric circuits.     

Ce3+-Gd3+ co-doped high efficiency oxide glasses and transfer efficiency from Gd3+ to Ce3+

The rare earth Ce3+ ion doped SiO2-B2O3-BaO-Gd2O3 system is synthesized by high-temperature melting method. The density, transmission, excitation spectra and scintillating properties of the glasses are investigated. The results indicate that all the samples have good physical and scintillating properties. The emission peak wavelength of all samples is 390 nm under X-ray radiation. Gd3+ ions have a negative impact on scintillating properties when its concentration reaches a certain level. Gd3+ ions sensitize the luminescence of Ce3+ ions, and the ideal concentration is 15 mol% for Gd3+ ions. Also the decay characteristics of Ce3+ and Gd3+ ions are investigated. These samples have potential practical applications in high energy physics.     

Ti3+ Self‐Doped Dark Rutile TiO2 Ultrafine Nanorods with Durable High‐Rate Capability for Lithium‐Ion Batteries

Dark‐colored rutile TiO₂ nanorods doped by electroconducting Ti³⁺ have been obtained uniformly with an average diameter of ≈7 nm, and have been first utilized as anodes in lithium‐ion batteries. They deliver a high reversible specific capacity of 185.7 mAh g^?1 at 0.2 C (33.6 mA g^?1) and maintain 92.1 mAh g^?1 after 1000 cycles at an extremely high rate 50 C with an outstanding retention of 98.4%. Notably, the coulombic efficiency of Ti³⁺–TiO₂ has been improved by approximately 10% compared with that of pristine rutile TiO₂, which can be mainly attributed to its prompt electron transfer because of the introduction of Ti³⁺. Again the synergetic merits are noticed when the promoted electronic conductivity is combined with a shortened Li⁺ diffusion length resulting from the ultrafine nanorod structure, giving rise to the remarkable rate capabilities and extraordinary cycling stabilities for applications in fast and durable charge/discharge batteries. It is of great significance to incorporate Ti³⁺ into rutile TiO₂ to exhibit particular electrochemical characteristics triggering an effective way to improve the energy storage properties.     

A Series of Hybrid Multifunctional Interfaces as Artificial SEI Layer for Realizing Dendrite Free,and Long-Life Sodium Metal Anodes (Adv. Funct. Mater. 42/2023)

Sodium metal (Na) anodes are considered the most promising anode for high-energy-density sodium batteries because of their high capacity and low electrochemical potential. However, Na metal anode undergoes uncontrolled Na dendrite growth, and unstable solid electrolyte interphase layer (SEI) formation during cycling, leading to poor coulombic efficiency, and shorter lifespan. Herein, a series of Na-ion conductive alloy-type protective interface (Na-In, Na-Bi, Na-Zn, Na-Sn) is studied as an artificial SEI layer to address the issues. The hybrid Na-ion conducting SEI components over the Na-alloy can facilitate uniform Na deposition by regulating Na-ion flux with low overpotential. Furthermore, density functional study reveals that the lower surface energy of protective alloys relative to bare Na is the key factor for facilitating facile ion diffusion across the interface. Na metal with interface layer facilitates a highly reversible Na plating/stripping for ≈790 h, higher than pristine Na metal (100 h). The hybrid self-regulating protective layers exhibit a high mechanical flexibility to promote dendrite free Na plating even at high current density (5 mA cm⁻²), high capacity (10 mAh cm⁻²), and good performance with Na₃V₂(PO₄)₃ cathode. The current study opens a new insight for designing dendrite Na metal anode for next generation energy storage devices.     

Boosting Kinetics of Ce3+/Ce4+ Redox Reaction by Constructing TiC/TiO2 Heterojunction for Cerium-Based Flow Batteries

Cerium, a unique rare earth element, possesses a relatively high abundance, low cost, and high redox voltage, making it an attractive candidate for redox flow batteries. However, the sluggish kinetics and corrosion nature of the Ce³⁺/Ce⁴⁺ electrolyte result in overpotential and degradation of carbon felt (CF) electrodes, which hinders the development of cerium-based flow batteries. Therefore, it is essential to develop an electrode with high catalytic activity and corrosion resistance to the Ce³⁺/Ce⁴⁺ electrolyte. Herein, a TiC/TiO₂ coated carbon felt (TiC/TiO₂-CF) electrode is proposed. Remarkably, the TiC/TiO₂ coating effectively minimizes the exposure of the CF to the highly corrosive cerium electrolyte, consequently enhancing the electrode's corrosion resistance. Additionally, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy characterizations reveal the formation of a heterojunction between TiC and TiO₂, which significantly enhances the redox reaction kinetics of the Ce³⁺/Ce⁴⁺ redox couple. Eventually, the practical application of TiC/TiO₂-CF catalytic electrode in a Ce–Fe flow battery is demonstrated. This study sheds light on the synthesis conditions of the TiC/TiO₂-CF electrode, elucidates its heterojunction structure, and presents a novel Ce–Fe flow battery system.     

A Ca-Ion Electrochromic Battery via a Water-in-Salt Electrolyte

Multivalent-ion batteries with electrochromic functionality are an emerging green technology for development of low-carbon society. Compared to Mg²⁺, Zn²⁺ and Al³⁺, Ca²⁺ has a low polarization strength similar to that of Li⁺, therefore Ca²⁺ for electrochromism and battery can avoid kinetic issues caused by other multivalent-ions with high polarization strength. Here, by exploiting Ca-ion carriers for electrochromism and a water-in-salt (WIS) Ca(OTF)₂ electrolyte for the first time, a new and safe aqueous Ca-ion electrochromic battery (CIEB) has been demonstrated. The WIS Ca(OTF)₂ electrolyte demonstrates enhanced anion-cation interactions and decreased water activity. Vanadium oxide (VO_x) and indium hexacyanoferrate (InHCF) films are respectively developed as anode and cathode because of their stable and high-rate Ca²⁺ insertion/extraction, as well as matched electrochromism. The CIEB demonstrates a stable and high-rate capability, a high energy density of 51.4 mWh m⁻² at a power density of 1737.3 mW m⁻², and a greenish yellow-to-black electrochromism. The presented results are beneficial for understanding redox kinetics in WIS electrolytes, and inspire researches on batteries and electrochromism with multivalent-ions.     

A Scalable Free‐Standing V2O5/CNT Film Electrode for Supercapacitors with a Wide Operation Voltage (1.6 V) in an Aqueous Electrolyte

While vanadium oxides have many attractive pseudocapacitive features for energy storage, their applications are severely limited by the poor electronic conductivity and low specific surface area. To overcome these limitations, a scalable, free‐standing film electrode composed of intertwined V₂O₅ nanowires and carbon nanotubes (CNTs) using a blade coating process has been prepared. The unique architecture of this hybrid electrode greatly facilitates electronic transport along CNTs while maintaining rapid ion diffusion within V₂O₅ nanowires and fast electron transfer across the V₂O₅/CNTs interfaces. When tested in a neutral aqueous electrolyte, this hybrid film electrode demonstrates a volumetric capacitance of ≈460 F cm^?3. Moreover, a symmetric capacitor based on two identical film electrodes displays a wide operation voltage window of 1.6 V, delivering a volumetric energy density as high as 41 Wh L^?1.     

Dual Functions of CO2 Molecular Activation and 4f Levels as Electron Transport Bridge in Dysprosium Single Atom Composite Photocatalysts with Enhanced Visible-Light Photoactivities

The effect of rare earth (RE) single atoms on photocatalytic activity is very complex due to its special electronic configuration, which leads to few reports on the RE single atoms. Here, Dy³⁺ single atom composite photocatalysts are successfully constructed based on both the special role of Dy³⁺ and the special advantages of CdS/g-C₃N₄ heterojunction in the field of photocatalysis. The results show that an efficient way of electron transfer is provided to promote charge separation, and the dual functions of CO₂ molecular activation of rare-earth single atom and 4f levels as electron transport bridge are fully exploited. It is exciting that under visible-light irradiation, the catalytic performance of CdS:Dy³⁺/g-C₃N₄ is ≈ 6.9 times higher than that of pure g-C₃N₄. The catalytic performance of CdS:Dy³⁺ and CdS:Dy³⁺/g-C₃N₄ are ≈ 7 and ≈ 13.7 times higher than those of pure CdS, respectively. Besides, not all RE ions are suitable for charge transfer bridges, which is not only related to the 4f levels of RE ions but also related to the bandgap structure of CdS and g-C₃N₄. The pattern of combining single-atom catalysis and heterojunction opens up new methods for enhancing photocatalytic activity.     

Structural and Electrical Properties of Atomic Layer Deposited Al‐Doped ZnO Films

Structural and electrical properties of Al‐doped ZnO (AZO) films deposited by atomic layer deposition (ALD) are investigated to study the extrinsic doping mechanism of a transparent conducting oxide. ALD‐AZO films exhibit a unique layer‐by‐layer structure consisting of a ZnO matrix and Al₂O₃ dopant layers, as determined by transmission electron microscopy analysis. In these layered AZO films, a single Al₂O₃ dopant layer deposited during one ALD cycle could provide ≈4.5 × 10¹³ cm^?2 free electrons to the ZnO. The effective field model for doping is suggested to explain the decrease in the carrier concentration of ALD‐AZO films when the interval between the Al₂O₃ layers is reduced to less than ≈2.6 nm (>3.4 at% Al). By correlating the electrical and structural properties, an extrinsic doping mechanism of ALD‐AZO films is proposed in which the incorporated Al atoms take oxygen from the ZnO matrix and form doubly charged donors, such as oxygen vacancies or zinc interstitials.     

Internal electrochromism in vanadium pentoxide xerogel films

We describe the internal electrochromic effect in V₂O₅ xerogel films caused by the redistribution of hydrogen ions inside the film, instead of insertion from the outside, i.e. from an electrolyte, as in the case of conventional electrochromism. A hypothesis is put forward according to which the mechanism of this electrochromic effect is associated with formation of red-colored hexa- and (or) deca-vanadic acid inclusions inside the vanadium pentoxide layers. This model is supported by the calculated data of energy characteristics of V–O chemical bonds in V₂O₅ octahedra layers of xerogel, as well as by the experimental results of XRD, FTIR, and optical spectroscopy.