Microwave-Absorbing Foams with Adjustable Absorption Frequency and Structural Coloration.

Microwave-absorbing materials with regulatable absorption frequency and optical camouflage hold great significance in intelligent electronic devices and advanced stealth technology. Herein, we present an innovative microwave-absorbing foam that can dynamically tune microwave absorption frequencies via a simple mechanical compression while in parallel enabling optical camouflage over broad spectral ranges by adjusting the structural colors. The vivid colors spanning different color categories generated from thin-film interference can be precisely regulated by adjusting the thickness of the conformal TiO2 coatings on Ni/melamine foam. Enhanced interfacial and defect-induced polarizations resulting from the introduction of TiO2 coating synergistically contribute to the dielectric attenuation performance. Consequently, such a foam exhibits exceptional microwave absorption capabilities, and the absorption frequency can be dynamically tuned from the S band to the Ku band by manipulating its compression ratio. Additionally, simulation calculations validate the adjustable electromagnetic wave loss behavior, offering valuable insights for the development of next-generation intelligent electromagnetic devices across diverse fields.

Low-Concentration Redox-Electrolytes for High-Rate and Long-Life Zinc Metal Batteries.

The uncontrolled zinc electrodeposition and side reactions severely limit the power density and lifespan of Zn metal batteries. Herein, the multi-level interface adjustment effect is realized with low-concentration redox-electrolytes (0.2 m KI) additives. The iodide ions adsorbed on the zinc surface significantly suppress water-induced side reactions and by-product formation and enhance the kinetics of zinc deposition. The distribution of relaxation times results reveal that iodide ions can reduce the desolvation energy of hydrated zinc ions and guide the deposition of zinc ions due to their strong nucleophilicity. As a consequence, the Zn||Zn symmetric cell achieves superior cycling stability (>3000 h at 1 mA cm-2 , 1 mAh cm-2 ) accompanied by a uniform deposition and a fast reaction kinetics with a low voltage hysteresis (<30 mV). Additionally, coupled with an activated carbon (AC) cathode, the assembled Zn||AC cell delivers a high-capacity retention of 81.64% after 2000 cycles at 4 A g-1 . More importantly, the operando electrochemical UV-vis spectroscopies show that a small number of I3 - can spontaneously react with the dead zinc as well as basic zinc saltsand regenerate iodide ions and zinc ions; thus, the Coulombic efficiency of each charge-discharge process is close to 100%.

A Covalent Organic Framework as a Long-life and High-Rate Anode Suitable for Both Aqueous Acidic and Alkaline Batteries.

Aqueous rechargeable batteries are prospective candidates for large-scale grid energy storage. However, traditional anode materials applied lack acid-alkali co-tolerance. Herein, we report a covalent organic framework containing pyrazine (C=N) and phenylimino (-NH-) groups (HPP-COF) as a long-cycle and high-rate anode for both acidic and alkaline batteries. The HPP-COF's robust covalent linkage and the hydrogen bond network between -NH- and water molecules collectively improve the acid-alkaline co-tolerance. More importantly, the hydrogen bond network promotes the rapid transport of H+ /OH- by the Grotthuss mechanism. As a result, the HPP-COF delivers a superior capacity and cycle stability (66.6 mAh g-1 @ 30 A g-1 , over 40000 cycles in 1 M H2 SO4 electrolyte; 91.7 mAh g-1 @ 100 A g-1 , over 30000 cycles @ 30 A g-1 in 1 M NaOH electrolyte). The work opens a new direction for the structural design and application of COF materials in acidic and alkaline batteries.

Regulating Exposed Facets of Metal-Organic Frameworks for High-rate Alkaline Aqueous Zinc Batteries.

Metal-organic frameworks (MOFs) have drawn growing attention as promising electrode candidates for rechargeable batteries. However, most studies focus on the direct use of MOF electrodes without any modification. Post-synthetic modification, a judicious tool to modify targeted properties of MOFs, has been long-neglected in the field of batteries. Herein, crystal-facet engineering is proposed to design MOF-based electrodes with high capacity and fast electrochemical kinetics. We found that a thermally-modified strategy can regulate the dominant exposed facet of Ni-based MOF (PFC-8). With the optimally exposed facets, the battery exhibited admirable rate capability (139.4 mAh g-1 at 2.5 A g-1 and 110.0 mAh g-1 at 30 A g-1 ) and long-term stability. Furthermore, density functional theory calculations demonstrate that stronger OH- adsorption behaviors and optimized electronic structures induced by the regulated exposed facets boost the electrochemical performance.

High-Energy Aqueous Magnesium Hybrid Full Batteries Enabled by Carrier-Hosting Potential Compensation.

Underachieved capacity and low voltage plateau is ubiquitous in conventional aqueous magnesium ion full batteries. Such limitations originate from the electrochemistry and the low carrier-hosting ((de)intercalation) potential of electrode materials. Herein, via a strategy of enhancing the electrochemistry through carrier-hosting potential compensation, high-energy Mg2+ /Na+ hybrid batteries are achieved. A Mg1.5 VCr(PO4 )3 (MVCP) cathode is coupled with FeVO4 (FVO) anode in a new aqueous/organic hybrid electrolyte, giving reliable high-voltage operation. This operation enables more sufficient (de)intercalation of hybrid carriers (Mg2+ /Na+ ), thereby enhancing the reversible capacity remarkably (233.4 mA h g-1 at 0.5 A g-1 , 92.7 Wh kg-1 electrode , that is, ≥1.75-fold higher than those in conventional aqueous electrolytes). The relatively high Na+ -hosting potential of the electrodes compensates for the low Mg2+ -hosting potential and widens/elevates the discharge plateau of the full battery up to 1.50 V. Mechanism study further reveals an unusual phase transformation of FVO to Fe2 V3 and the low-lattice-strain pseudocapacitive (de)intercalation chemistry of MVCP.

Boosting the Cycling Stability of Aqueous Flexible Zn Batteries via F Doping in Nickel-Cobalt Carbonate Hydroxide Cathode.

Cathodes of rechargeable Zn batteries typically face the issues of irreversible phase transformation, structure collapse, and volume expansion during repeated charge/discharge cycles, which result in an increased transfer resistance and poor long-term cycling stability. Herein, a facile F doping strategy is developed to boost the cycling stability of nickel cobalt carbonate hydroxide (NiCo-CH) cathode. Benefiting from the extremely high electronegativity, the phase and morphology stabilities as well as the electrical conductivity of NiCo-CH are remarkably enhanced by F incorporation (NiCo-CH-F). Phase interface and amorphous microdomains are also introduced, which are favorable for the electrochemical performance of cathode. Benefiting from these features, NiCo-CH-F delivers a high capacity (245 mA h g-1 ), excellent rate capability (64% retention at 8 A g-1 ), and outstanding cycling stability (maintains 90% after 10 000 cycles). Moreover, the quasi-solid-state battery also manifests superior cycling stability (maintains 90% after 7200 cycles) and desirable flexibility. This work offers a general strategy to boost the cycling stability of cathode materials for aqueous Zn batteries.

Direct Dynamic Evidence of Charge Separation in a Dye-Sensitized Solar Cell Obtained under Operando Conditions by Raman Spectroscopy.

Interfaces play an important role in enhancing the energy conversion performance of dye-sensitized solar cells (DSCs). The interface effects have been studied by many techniques, but most of the studies only focused on one part of a DSC, rather than on a complete solar cell. Hence, monitoring the interface evolution of a DSC is still very challenging. Here, in situ/operando resonance Raman (RR) spectroscopic analyses were carried out to monitor the dynamics of the photovoltaic conversion processes in a DSC. We observed the creation of new species (i.e., polyiodide and iodine aggregates) in the photosensitization process. We also obtained molecular-scale dynamic evidence that the bands from the C=C and C=N bonds of 2,2'-bipyridyl (bpy), the S=C=N bonds of the NCS ligand, and photochemical products undergo reasonably strong intensity and frequency changes, which clearly demonstrates that they are involved in charge separation. Furthermore, RR spectroscopy can also be used to quickly evaluate the performance of DSCs.

Patterned polyaniline encapsulated in titania nanotubes for electrochromism.

In this article, we report the preparation of a TiO2 nanotube array (TNA) film used as a transparent electrochromic material and a TNA/polyaniline patterned hybrid electrochromic film utilized as an information display material. The TNA film was fabricated by an anodizing process, and a surface patterned TNA with extreme wettability contrast (hydrophilic/hydrophobic) on a TNA surface through self-assembly (SAM) and photocatalytic lithography is fabricated. Then the TNA/polyaniline hybrid film was prepared by electrodeposition of aniline in an aqueous solution. Finally, the electrochromic properties of the TNA film and the TNA/polyaniline hybrid film were investigated. Compared with neat TNA film and polyaniline (PANI) films, the hybrid film shows a much higher optical contrast in the near infrared range. The TNA/polyaniline hybrid film shows higher coloration efficiencies of 24.4 cm2 C-1 at a wavelength of 700 nm and 17.1 cm2 C-1 at a wavelength of 1050 nm compared to the TNA coloration efficiency. The color switching time (20.9 s or 22.9 s) of TNA/polyaniline is faster than TNA.

Development of Inverse-Opal-Structured Charge-Deficient Co9S8@nitrogen-Doped-Carbon to Catalytically Enable High Energy and High Power for the Two-Electron Transfer I+/I- Electrode.

The iodine (I) electrode involving two-electron transfer chemistry by converting between I+ and I-, has the potential to deliver theoretically doubled capacity and higher working voltage platforms, thus achieving higher energy density. However, owing to the slow kinetics of the cascade two-electron transfer reactions, the system suffers from large overpotentials and low power density, especially at high working currents and low temperatures. Here, an inverse-opal-structured cobalt sulfide@nitrogen-doped-carbon (Co9S8@NC) catalyst with unique charge-deficient states is developed to promote the reaction kinetics of the I-/I+ electrode. The charge-deficient Co9S8@NC catalyst not only enables strong physicochemical adsorption with the iodine species but also significantly reduces the activation energy and interfacial charge transfer resistance of the cascade I+/I0/I- conversion reaction. Consequently, the prototypical Zn‖I+/I0/I- battery equipped with the Co9S8@NC catalyst can deliver a high energy density of 554 Wh kg-1 and a stable cycle life of 5000 cycles at 30 °C. Moreover, at a subzero temperature of -30 °C, the battery can exhibit enhanced kinetics and a high power density of 1514 W kg-1, high energy density of 485 Wh kg-1.

Cross-linked polyaniline for production of long lifespan aqueous iron||organic batteries with electrochromic properties.

Aqueous iron batteries are appealing candidates for large-scale energy storage due to their safety and low-cost aspects. However, the development of aqueous Fe batteries is hindered by their inadequate long-term cycling stability. Here, we propose the synthesis and application as positive electrode active material of cross-linked polyaniline (C-PANI). We use melamine as the crosslinker to improve the electronical conductivity and electrochemical stability of the C-PANI. Indeed, when the C-PANI is tested in combination with a Fe metal negative electrode and 1 M iron trifluoromethanesulfonate (Fe(TOF)2) electrolyte solution, the coin cell can deliver a specific capacity of about 110 mAh g-1 and an average discharge voltage of 0.55 V after 39,000 cycles at 25 A g-1 with a test temperature of 28 °C ± 1 °C. Furthermore, mechanistic studies suggest that Fe2+ ions are bonded to TOF- anions to form positively charged complexes Fe(TOF)+, which are stored with protons in the C-PANI electrode structures. Finally, we also demonstrate the use of C-PANI in combination with a polymeric hydrogel electrolyte to produce a flexible reflective electrochromic lab-scale iron battery prototype.

A Static Tin-Manganese Battery with 30000-Cycle Lifespan Based on Stabilized Mn3+/Mn2+ Redox Chemistry.

High-potential Mn3+/Mn2+ redox couple (>1.3 V vs SHE) in a static battery system is rarely reported due to the shuttle and disproportionation of Mn3+ in aqueous solutions. Herein, based on reversible stripping/plating of the Sn anode and stabilized Mn2+/Mn3+ redox couple in the cathode, an aqueous Sn-Mn full battery is established in acidic electrolytes. Sn anode exhibits high deposition efficiency, low polarization, and excellent stability in acidic electrolytes. With the help of H+ and a complexing agent, a reversible conversion between Mn2+ and Mn3+ ions takes place on the graphite surface. Pyrophosphate ligand is initially employed to form a protective layer through a complexation process with Sn4+ on the electrode surface, effectively preventing Mn3+ from disproportionation and hindering the uncontrollable diffusion of Mn3+ to electrolytes. Benefiting from the rational design, the full battery delivers satisfied electrochemical performance including a large capacity (0.45 mAh cm-2 at 5 mA cm-2), high discharge plateau voltage (>1.6 V), excellent rate capability (58% retention from 5 to 30 mA cm-2), and superior cycling stability (no decay after 30 000 cycles). The battery design strategy realizes a robustly stable Mn3+/Mn2+ redox reaction, which broadens research into ultrafast acidic battery systems.

Hydrogel Electrolyte with High Tolerance to a Wide Spectrum of pHs and Compressive Energy Storage Devices Based on It.

Normally, hydrogel electrolytes widely used in flexible energy storage devices have limited tolerance to different pHs. Most gel electrolytes will lose their compressible capability when the adaptable pH is changed. Herein, a poly(acrylamide3 -co-(sulfobetaine methacrylate)1 )@polyacrylamide (P(A3 -co-S1 )@PAM) hydrogel electrolyte equipped with a dual crosslinking network (DN) is successfully fabricated, which exhibits excellent tolerance to any pHs, endowing various energy storage devices including batteries and supercapacitors with superior mechanical durability. The batteries with mild and alkaline P(A3 -co-S1 )@PAM electrolytes display superior stability (over 3000 cycles). Additionally, a Zn||MnO2 battery based on the P(A3 -co-S1 )@PAM hydrogel electrolyte (mild) under 50% compression strain also shows excellent charge-discharge stability and high capacity at 152.4 mAh g-1 after 600 cycles. The strong reversible hydrogen bonds and electrostatic forces originating from zwitterionic structures of poly(sulfobetaine methacrylate) play an important role in dissipating and dispersing energy imposed abruptly. Meanwhile, the zwitterionic structure and intermolecular NH⋯OC hydrogen bonds of the hydrogel lead to the property of acid resistance and alkali resistance. The tough and robust covalent crosslinking bonds and the tight arrangement of DN polymer chains enable the hydrogel electrolytes to recover their initial shape fast once unloading.

Manipulating coordination environment for a high-voltage aqueous copper-chlorine battery.

Aqueous copper-based batteries have many favourable properties and have thus attracted considerable attention, but their application is limited by their low operating voltage originating from the high potential of copper negative electrode (0.34 V vs. standard hydrogen electrode). Herein, we propose a coordination strategy for reducing the intrinsic negative electrode redox potential in aqueous copper-based batteries and thus improving their operating voltage. This is achieved by establishing an appropriate coordination environment through the electrolyte tailoring via Cl- ions. When coordinated with chlorine, the intermediate Cu+ ions in aqueous electrolytes are successfully stabilized and the electrochemical process is decoupled into two separate redox reactions involving Cu2+/Cu+ and Cu+/Cu0; Cu+/Cu0 results in a redox potential approximately 0.3 V lower than that for Cu2+/Cu0. Compared to the coordination with water, the coordination with chlorine also results in higher copper utilization, more rapid redox kinetics, and superior cycle stability. An aqueous copper-chlorine battery, harnessing Cl-/Cl0 redox reaction at the positive electrode, is discovered to have a high discharge voltage of 1.3 V, and retains 77.4% of initial capacity after 10,000 cycles. This work may open up an avenue to boosting the voltage and energy of aqueous copper batteries.

Rechargeable Iodine Batteries: Fundamentals, Advances, and Perspectives.

Lattice distortion and structure collapse are two intrinsic issues of intercalative-type electrodes derived from repeated ion shuttling. In contrast, rechargeable iodine batteries (RIBs) based on the conversion reaction of iodine stand out for high reversibility and satisfying voltage output characteristics no matter when dealing with both monovalent and multivalent ions. Foreseeable performance superiorities lead to an influx of considerable focus and thus a renaissance in RIBs. This review provides a comprehensive overview of the fundamental chemistry of RIBs from the perspectives of physicochemical properties, conversion mechanism, and existing issues. Furthermore, we refine the optimization strategies for high-performance RIBs, focusing on physical adsorption and chemical interaction strengthening, electrolytes regulation, and nanoscale-iodine design. Then the pros and cons of tremendous RIBs are compared and specified. Ultimately, we conclude with remaining challenges and perspectives to our best knowledge, which may inspire the construction of next-generation RIBs.

High-Rate Aqueous Aluminum-Ion Batteries Enabled by Confined Iodine Conversion Chemistry.

Most reported cathode materials for rechargeable aqueous Al metal batteries are based on an intercalative-type chemistry mechanism. Herein, iodine embedded in MOF-derived N-doped microporous carbon polyhedrons (I2 @ZIF-8-C) is proposed to be a conversion-type cathode material for aqueous aluminum-ion batteries based on "water-in-salt" electrolytes. Compared with the conventional Al-I2 battery using ionic liquid electrolyte, the proposed aqueous Al-I2 battery delivers much enhanced electrochemical performance in terms of specific capacity and voltage plateaus. Benefitting from the confined liquid-solid conversion of iodine in hierarchical N-doped microporous carbon polyhedrons and enhanced reaction kinetics of aqueous electrolytes, the I2 @ZIF-8-C electrode delivers high reversibility, superior specific capacity (≈219.8 mAh g-1 at 2 A g-1 ), and high rate performance (≈102.6 mAh g-1 at 8 A g-1 ). The reversible reaction between I2 and I- , with I3 - and I5 - as intermediates, is confirmed via ex situ Raman spectra and X-ray photoelectron spectroscopy. Furthermore, solid-state hydrogel electrolyte is employed to fabricate a flexible Al-I2 battery, which shows performance comparable to batteries using liquid electrolyte and can be integrated to power wearable devices as a reliable energy supply.

Recent advances in flexible aqueous zinc-based rechargeable batteries.

Flexible aqueous Zn battery has exhibited great potential as a power source for flexible and wearable electronic devices due to its unique features, such as high safety, low cost, and eco-friendliness. Numerous studies on flexible Zn batteries have been reported and exciting achievements have been obtained in the past few years. However, there are still many problems in the electrode design and the assembly process to acquire desirable flexibility without sacrificing the capacity. This review summarizes the up-to-date advances in flexible Zn batteries. We first introduce the recent progresses in anodes, cathodes and solid-state electrolytes. Special emphases are then put on the discussions of differences between various flexible current collectors or substrates. Electrode preparation techniques and flexible battery assembly technologies are also compared and discussed. Finally, challenges toward further developments of flexible Zn batteries with high capacity, excellent flexibility and cycling stability are proposed. Future research trends and highlights are suggested as well.

A FRET-based fluorescent and colorimetric probe for the specific detection of picric acid.

Picric acid (PA) as an environmental pollutant and high explosive, has recently received considerable attention. In this paper, a novel fluorescent and colorimetric chemo-probe (L) for the highly selective and sensitive detection of picric acid has been revealed. The probe was facilely constructed using rhodamine B, ethylenediamine and 4-(9H-carbazol-9-yl)benzoyl chloride. Significant fluorescence changes based on an intramolecular fluorescence resonance energy transfer (FRET) effect followed by a distinct color change from colorless to pink were observed after addition of picric acid to the probe solution. Selectivity measurements revealed that the as-synthesized probe exhibited high selectivity toward PA in the presence or absence of other analytes. The experimental titration results suggested that the as-synthesized probe is an effective tool for detection of PA with a nanomolar scale detection limit (820 nM) and could also serve as a "naked-eye" indicator for PA detection.

Improved Electrochromic Performance of Poly(3,4-ethylenedioxythiophene) by Incorporating a Three-Dimensionally Ordered Macroporous Structure.

In this paper, three-dimensionally ordered macroporous (3DOM) poly(3,4-ethylenedioxythiophene) (PEDOT) films were electropolymerized from an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6 ). The electrochromic performances of the 3DOM PEDOT films were studied. The 3DOM films exhibited high transmittance modulation (41.2 % at λ=580 nm), high ionic fast switching speeds (0.7 and 0.7 s for coloration and bleaching, respectively), and enhanced cycling stability relative to that exhibited by the dense PEDOT film. The relationship between the declining behavior of the transmittance modulation and the nanostructure of the film was investigated. A three-period decay process was proposed to understand the declining behavior. The 3D interconnected macroporous nanostructure is beneficial for fast ion and electron transportation, high ion accessibility, and maintenance of structure integrity, which result in enhanced cycling stability and fast switching speeds.

Novel morphology changes from 3D ordered macroporous structure to V2O5 nanofiber grassland and its application in electrochromism.

Because vanadium pentoxide (V2O5) is the only oxide that shows both anodic and cathodic coloration electrochromism, the reversible lithium ion insertion/extraction processes in V2O5 lead to not only reversible optical parameter changes but also multicolor changes for esthetics. Because of the outstanding electrochemical properties of V2O5 nanofibers, they show great potential to enhance V2O5 electrochromism. However, the development and practical application of V2O5 nanofibers are still lacking, because traditional preparation approaches have several drawbacks, such as multiple processing steps, unsatisfactory electrical contact with the substrate, expensive equipment, and rigorous experimental conditions. Herein, we first report a novel and convenient strategy to prepare grass-like nanofiber-stacked V2O5 films by a simple annealing treatment of an amorphous, three-dimensionally ordered macroporous vanadia film. The V2O5 nanofiber grassland exhibits promising transmittance modulation, fast switching responses, and high color contrast because of the outstanding electrochemical properties of V2O5 nanofibers as well as the high Li-ion diffusion coefficients and good electrical contact with the substrate. Moreover, the morphology transformation mechanism is investigated in detail.

Vibrational spectroscopy and density functional theory study of 4-mercaptobenzoic acid.

In this paper, 4-mercaptobenzoic acid (4-MBA/pMBA) was designed as a model molecule for theoretical and experimental studies of the molecule structure. Density functional theory (DFT) calculations have been performed to predict the IR and Raman spectra for the molecule. In addition, Fourier transform infrared (FTIR) and Raman spectra of the compound have been obtained experimentally. Based on the modeling results obtained at the B3LYP/6-311++G(∗∗) level, all FTIR and Raman bands of the compound obtained experimentally were assigned. Our calculated vibrational frequencies are in good agreement with the experimental vales. The molecular electrostatic potential surface calculation was performed and the result suggested that the 4-MBA had two hydrogen bond donors and three hydrogen bond acceptors. HOMO-LUMO gap was also obtained theoretically at B3LYP/6-311++G(∗∗) level.