Faradaic and Non-Faradaic Self-Discharge Mechanisms in Carbon-Based Electrochemical Capacitors.

Electrochemical capacitors (ECs) play a crucial role in electrical energy storage, offering great potential for efficient energy storage and power management. However, they face challenges such as moderate energy densities and rapid self-discharge. Addressing self-discharge necessitates a fundamental understanding of the underlying processes. This review sets itself apart from other reviews by focusing on the basic principles of self-discharge processes in carbon-based ECs, particularly examining the nature of the process and the involvement of redox reactions. This study delineates the potential conditions for various self-discharge processes and proposes plausible criteria for differentiation, complemented by mathematical modeling. Additionally, the model selection, curve fitting, and effective tuning methods are explored to control self-discharge processes.

In situ photocatalytically enhanced thermogalvanic cells for electricity and hydrogen production.

High-performance thermogalvanic cells have the potential to convert thermal energy into electricity, but their effectiveness is limited by the low concentration difference of redox ions. We report an in situ photocatalytically enhanced redox reaction that generates hydrogen and oxygen to realize a continuous concentration gradient of redox ions in thermogalvanic devices. A linear relation between thermopower and hydrogen production rate was established as an essential design principle for devices. The system exhibited a thermopower of 8.2 millivolts per kelvin and a solar-to-hydrogen efficiency of up to 0.4%. A large-area generator (112 square centimeters) consisting of 36 units yielded an open-circuit voltage of 4.4 volts and a power of 20.1 milliwatts, as well 0.5 millimoles of hydrogen and 0.2 millimoles of oxygen after 6 hours of outdoor operation.

Na Storage in Sb2S3@C Composite: A Synergistic Capacity Contribution Mechanism with Wider Temperature Adaptability.

The practical applications of metallic anodes are limited due to dendritic growth, propagation in an infinite volume during the plating process, and parasitic interfacial reactions between sodium (Na) and the electrolyte. Herein, we developed Sb2S3 microrods as a template to regulate the nucleation of metallic Na. Additionally, the propagation of the deposited metal could be spatially regulated via a "nanoconfinement effect", that is, within the conformal hard carbon (C) layer of nanothickness. Moreover, we carefully studied the seed effect of the in situ-formed Na-Sb and Na-S alloys within the hard C sheath during the Na plating process. The symmetrical cells of the Sb2S3@C composite anode achieved dendrite-free cycling at 1 mA cm-2 for 1100 h at a high capacity loading of 1 mA h cm-2 and considerably mitigated a nucleation overpotential of 20 mV. Pairing a NaVPO4F (NVPF) cathode (4.6 mg cm-2) with an in situ presodiation Sb2S3@C composite (2*Na excess) prototype delivered a high energy density and a high power density of 173.75 W h kg-1 and 868.57 W kg-1, respectively. Therefore, this study provides tremendous possibilities for employing the proposed hybrid storage mechanism in low-cost and practical applications of high-energy-density Na metal batteries.

Near Zero-Threshold Voltage P-N Junction Diodes Based on Super-Semiconducting Nanostructured Ag/Al Arrays.

Semiconductor devices are currently one of the most common energy consumption devices. Significantly reducing the energy consumption of semiconductor devices with advanced energy-efficient technologies is highly desirable. The discovery of super-semiconductors (SSCs) based on metallic bi-layer shell arrays provides an opportunity to realize ultra-low-power consumption semiconductor devices. As an example, the achievement of near zero-threshold voltage in p-n junction diodes based on super-semiconducting nanostructured Ag/Al arrays is reported, realizing ultra-low-power p-n junction diodes: ≈3 W per trillion diodes with a working voltage of 1 V or 30 mW per trillion diodes with an operating voltage of 0.1 V. In addition, the p-n junction diodes exhibit a high breakdown field of ≈1.1 × 106  V cm-1 , similar to that of SiC and GaN, due to a robust built-in field driven by infrared light photons. The SSC p-n diodes with near zero-threshold voltage and high breakdown field allow access to ultra-low-power semiconducting transistors, integrated circuits, chips, etc.

Boosting large-current-density water oxidation activity and stability by phytic acid-assisted rapid electrochemical corrosion.

Corrosion engineering is an efficient strategy to achieve durable oxygen evolution reaction (OER) catalysts at high current densities beyond 500 mA cm-2. However, the spontaneous electrochemical corrosion has a slow reaction rate, and most of them need to add large amounts of salts (such as NaCl) to accelerate the corrosion process. In this report, a novel and effective phytic acid (PA)-assisted in situ electrochemical corrosion strategy is demonstrated to accelerate the the corrosion process and form bimetallic active catalysts to show excellent OER performance at large current densities. In situ rapid electrochemical corrosion of nickel foam substrate and PA ligands etching realize localized high concentrations of Ni and Fe ions. High concentrations of metal ions will combine with hydroxyl to effectively form defects-enriched NiFe layered double hydroxides porous nanosheets tightly anchoring on the underneath substrate. Remarkably, the activated electrode exhibits excellent OER catalytic activities with ultralow overpotentials of 289 and 315 mV to reach high current densities of 500 and 1000 mA cm-2, respectively. When coupled with Ni-Mo-N hydrogen evolution reaction catalysts, the two-electrode cell merely requires 1.87 V to deliver 1000 mA cm-2. The ligands-assisted rapid electrochemical corrosion strategy provides a fresh perspective for facile, cost-effective, and scale-up production of superior OER catalysts at large current densities.

Ascorbic acid-induced fiber-scrolling of titanium carbide Ti3C2T x MXene.

Changing the morphology of two-dimensional materials often offers an efficient and effective means to exploit their electronic and mechanical properties. Two-dimensional materials such as graphene can be scrolled into one-dimensional fibers via simple sonication. Unfortunately, scrolling MXene nanosheets into fibers is quite challenging, especially Ti3C2T x composed of three layers of titanium atoms and two layers of carbon atoms. Herein, we report a new method to fabricate MXene fibers via ascorbic acid (AA) induced scrolling of Ti3C2T x nanosheets. An unusual AA-Ti3C2T x interaction is discovered in that intercalated AA molecules bind to and interact with the Ti3C2T x surface in the form of a hydrogen bonding-bonded assembly instead of as individual molecules, and a sheet-scrolling mechanism is proposed based on this interaction. The as-obtained MXene fibers exhibit a compact cross-section, and the diameter can be tailored from hundreds of nanometers to several micrometers through tuning the MXene/AA ratio. Moreover, the storage modulus of the MXene-fiber sponge attains its maximum value of ∼1 MPa when a unique morphology comprising both fibers and not-yet-scrolled sheets is presented. This work offers a new strategy of fiber-shaping MXenes for applications in structural composites and flexible electronics.

Structurally integrated 3D carbon tube grid-based high-performance filter capacitor.

Filter capacitors play a critical role in ensuring the quality and reliability of electrical and electronic equipment. Aluminum electrolytic capacitors are the most commonly used but are the largest filtering components, limiting device miniaturization. The high areal and volumetric capacitance of electric double-layer capacitors should make them ideal miniaturized filter capacitors, but they are hindered by their slow frequency responses. We report the development of interconnected and structurally integrated carbon tube grid-based electric double-layer capacitors with high areal capacitance and rapid frequency response. These capacitors exhibit excellent line filtering of 120-hertz voltage signal and volumetric advantages under low-voltage operations for digital circuits, portable electronics, and electrical appliances. These findings provide a sound technological basis for developing electric double-layer capacitors for miniaturizing filter and power devices.

Plasma-Wind-Assisted In2S3 Preparation with an Amorphous Surface Structure for Enhanced Photocatalytic Hydrogen Production.

Photocatalytic production from water is considered an effective solution to fossil fuel-related environmental concerns, and photocatalyst surface science holds a significant interest in balancing photocatalysts' stability and activity. We propose a plasma-wind method to tune the surface properties of a photocatalyst with an amorphous structure. Theoretical calculation shows that the amorphous surface structure can cause an unsaturated coordination environment to adjust the electron distribution, forming more adsorption sites. Thus, the photocatalyst with a crystal-amorphous (C-A) interface can strengthen light absorption, harvest photo-induced electrons, and enrich the active sites, which help improve hydrogen yield. As a proof of concept, with indium sulfide (In2S3) nanosheets used as the catalyst, an impressive hydrogen production rate up to 457.35 µmol cm-2 h-1 has been achieved. Moreover, after plasma-assisted treatment, In2S3 with a C-A interface can produce hydrogen from water under natural outdoor conditions. Following a six-hour test, the rate of photocatalytic hydrogen evolution is found to be 400.50 µmol cm-2 g-1, which demonstrates that a catalyst prepared through plasma treatment is both effective and highly practical.

Generation of Phenol and Molecular Hydrogen through Catalyst-Free C-H Activation of Benzene by Water Radical Cations.

Here, we report on the abundant formation of phenol and molecular hydrogen when benzene vapor was exposed to gas plasma generated by +5.5 kV corona discharge of water vapor in argon in the absence of oxygen. Systematic analysis using a series of isotopic standards (d6-benzene, D2O, and H218O) and benzene derivatives (mono-, di-, trichlorobenzene, and N,N-dimethylaniline) indicated that the formation of phenol occurred through the reaction between neutral benzene and the radical cation of water dimer, (H2O)2+•. A two-step reaction mechanism was proposed based on the results of experiments and DFT calculations: (1) the formation of (C6H6...H2O)+• intermediate through electrophilic addition; (2) the formation of C6H5OH+• through the release of H2 from the (C6H6...H2O)+• intermediate. Our findings offer a novel catalyst-free method to prepare phenol from benzene with phenol selectivity >90%.

Boosting photocatalytic hydrogen production from water by photothermally induced biphase systems.

Solar-driven hydrogen production from water using particulate photocatalysts is considered the most economical and effective approach to produce hydrogen fuel with little environmental concern. However, the efficiency of hydrogen production from water in particulate photocatalysis systems is still low. Here, we propose an efficient biphase photocatalytic system composed of integrated photothermal-photocatalytic materials that use charred wood substrates to convert liquid water to water steam, simultaneously splitting hydrogen under light illumination without additional energy. The photothermal-photocatalytic system exhibits biphase interfaces of photothermally-generated steam/photocatalyst/hydrogen, which significantly reduce the interface barrier and drastically lower the transport resistance of the hydrogen gas by nearly two orders of magnitude. In this work, an impressive hydrogen production rate up to 220.74 µmol h-1 cm-2 in the particulate photocatalytic systems has been achieved based on the wood/CoO system, demonstrating that the photothermal-photocatalytic biphase system is cost-effective and greatly advantageous for practical applications.

Inducing rapid polysulfide transformation through enhanced interfacial electronic interaction for lithium-sulfur batteries.

Sluggish dynamics of polysulfide (LiPS) conversion leads to reduced utilization of active sulfur and rapid capacity decay. Introducing catalysts into lithium-sulfur battery systems is a feasible and imperative strategy to tackle this problem. Previous research studies have mainly been focused on selecting new catalysts and design functional structures to improve performance, and ignoring the interaction between catalysts and their carriers. Herein, by simply fabricating a high-efficiency ZnS quantum dot@graphene nanosheet catalyst (ZnS QD@rGO), we utilized enhanced interfacial electronic interaction to accelerate polysulfide conversion for high energy density Li-S batteries. With the smaller size of ZnS, the interfacial electronic interaction becomes more enhanced, which was evidenced by DFT calculations and XPS experiments. After mixing with sulfur, the electrodes achieved a high capacity of 857.8 mA h g-1 at 1 C and a retention of 91.2% after 300 cycles. Also, a sulfur cathode with a high actual capacity of ∼4.0 mA h cm-2 could be obtained, with no obvious capacity decay within 100 cycles. We believe that this strategy represents a new perspective on designing efficient high-load electrodes for Li-S batteries.

Reduced-Graphene-Oxide-Guided Directional Growth of Planar Lithium Layers.

Rechargeable lithium (Li) metal batteries hold great promise for revolutionizing current energy-storage technologies. However, the uncontrollable growth of lithium dendrites impedes the service of Li anodes in high energy and safety batteries. There are numerous studies on Li anodes, yet little attention has been paid to the intrinsic electrocrystallization characteristics of Li metal and their underlying mechanisms. Herein, a guided growth of planar Li layers, instead of random Li dendrites, is achieved on self-assembled reduced graphene oxide (rGO). In situ optical observation is performed to monitor the morphology evolution of such a planar Li layer. Moreover, the underlying mechanism during electrodeposition/stripping is revealed using ab initio molecular dynamics simulations. The combined experiment and simulation results show that when Li atoms are deposited on rGO, each layer of Li atoms grows along (110) crystallographic plane of the Li crystals because of the fine in-plane lattice matching between Li and the rGO substrate, resulting in planar Li deposition. With this specific topographic characteristic, a highly flexible lithium-sulfur (Li-S) full cell with rGO-guided planar Li layers as the anode exhibits stable cycling performance and high specific energy and power densities. This work enriches the fundamental understanding of Li electrocrystallization without dendrites and provides guidance for practical applications.

Probing the dynamic evolution of lithium dendrites: a review of in situ/operando characterization for lithium metallic batteries.

During the operation of lithium metal batteries, the direct observation of the evolving characteristics of the deposited lithium is rather challenging in consideration of the requirements for the fast-tracking and high spatial resolution of the signals within native organic electrolytes. However, the weak scattering of electrons and X-rays with low-atomic-number lithium deteriorates the spectral resolution of the signals. Therefore, this mini-review compares various influencing factors that determine the lithium nucleation process based on electrochemical performance evaluations, including the artificial protective layer, electrolyte formulation, lithiophilic sites and hierarchies of the substrate; additionally, the possibility of the dynamic observations of chemical, electronic, and geometric changes during the operation of metallic batteries is exhibited. For each category of the technique, a brief account of the advancements of the characterizing equipment is followed with novel cell designs. Finally, the prospects that advance the precise description of the lithium nucleation process are summarized. This mini-review highlights the mitigating strategies of lithium dendrites at molecular, electrode, and device levels and summarizes the state-of-the-art in operando techniques, thereby promoting the future design of metallic battery systems.

Normalized Lithium Growth from the Nucleation Stage for Dendrite-Free Lithium Metal Anodes.

Inducing uniform deposition of lithium from the stage of metal crystallization nucleation is of vital importance to achieve dendrite-free lithium anodes. Herein, using experiments and simulation, homogenization of Li nucleation and normalization of Li growth can be achieved on PNIPAM polymer brushes with lithiophilic functional groups modified Cu substrates. The lithiophilic functional groups of amide O can homogenize ion mass transfer and induce the uniform distribution of Li nucleation sites. What is more, the ultra-small space between each brush can act as the channels for Li transportation and normalization growth. Owing to the synergistic effect of homogenization and normalization of electrodeposited Li, the obtained planar columnar Li anode exhibits excellent cycle stability at an ultra-high current density of 20 mA cm-2 .

Hollow Carbon Nanospheres with Developed Porous Structure and Retained N Doping for Facilitated Electrochemical Energy Storage.

Development of highly porous carbons with abundant surface functionalities and well-defined nanostructure is of significance for many important electrochemical energy storage systems. However, porous carbons suffer from a compromise between porosity, doped functionality, and nanostructure that have thus far restricted their performances. Here, we report the design of highly porous, nitrogen-enriched hollow carbon nanospheres (PN-HCNs) by an interfacial copolymerization strategy followed by NH3-assisted carbonization, and further demonstrate their significance and effectiveness in enhancing the electrochemical performances. The PN-HCN simultaneously delivers a large surface area (1237 m2 g-1) and high N functionalities (6.25 atom %) with a remarkable efficiency of the surface area increase to N loss ratio enabled by NH3 treatment while inheriting the hollow nanospherical structure. Accordingly, owing to the enhanced surface area and retained N doping, the prepared PN-HCN demonstrates outstanding electrochemical performances as a cathode host in lithium-sulfur batteries, including a near-to-theoretical capacity of 1620 mAh g-1, high rate capability and good cycling stability (789 mAh g-1 at 0.5C after 200 cycles). These results are superior to those of HCN without NH3 treatment. Also, PN-HCN exhibits superior capacitances (203 F g-1) and fast ion transport ability in supercapacitors. Our finding shows the simultaneous achievement of both highly porous structures and sufficient N functionalities for high-performance applications.

Energy-storage covalent organic frameworks: improving performance via engineering polysulfide chains on walls.

The aligned one-dimensional channels found in covalent organic frameworks offer a unique space for energy storage. However, physical isolation of sulfur in the channels is not sufficient to prevent the shuttle of lithium-sulfide intermediates that eventually results in a poor performance of lithium-sulfur energy storage. Herein, we report a strategy based on imine-linked frameworks for addressing this shuttle issue by covalently engineering polysulfide chains on the pore walls. The imine linkages can trigger the polymerization of sulfur to form polysulfide chains and anchor them on the channel walls. The immobilized polysulfide chains suppress the shuttle effect and are highly redox active. This structural evolution induces multifold positive effects on energy storage and achieves improved capacity, sulfur accessibility, rate capability and cycle stability. Our results suggest a porous platform achieved by pore wall engineering for tackling key issues in energy storage.

High-K dielectric sulfur-selenium alloys.

Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications.

Dual Functionalities of Few-Layered Boron Nitrides in the Design and Implementation of Ca(OH)2 Nanomaterials toward an Efficient Wall Painting Fireproofing and Consolidation.

Preserving ancient wall paintings from damage has become a challenge over the years. Nanosized calcium hydroxide (Ca(OH)2) has been identified as a promising material to preserve wall paintings. However, the synthesis of nanosized Ca(OH)2 is extremely difficult. Here, we demonstrate a breakthrough in wall painting protection enabled by boron nitride nanosheets (BNNSs) through strategic synthesis Ca(OH)2-BNNS nanohybrids using an aqueous method. The BNNS have two significant functionalities in the design and implementation of the Ca(OH)2 nanomaterials. First, the introduction of BNNS results in the successful synthesis of uniform and nanosized Ca(OH)2 (∼80 nm) in the nanohybrids, which can be attributed to the supersaturation-induced "etching-stripping" mechanism. More interestingly and importantly, a unique gradient penetration structure is strategically formed when applying Ca(OH)2-BNNS hybrids on the wall paintings, i.e., the BNNS-rich layer will be at the surface of wall painting, whereas Ca(OH)2 nanomaterials prefer to penetrate deep in to the wall paintings. This gradient structure will allow the BNNS-rich layer to protect the wall paintings from fire, which is the first report to date among the protection materials for wall paintings; at the same time, nanosized Ca(OH)2 shows superior wall painting consolidation strength compared to commercial Ca(OH)2 material. These results endow new applications of the newly emerging two-dimensional nanomaterials for protecting cultural heritage.

Flexible Sub-Micro Carbon Fiber@CNTs as Anodes for Potassium-Ion Batteries.

Potassium-ion batteries (KIBs) with potential cost benefits are a promising alternative to lithium-ion batteries (LIBs). However, because of the large radius of K+, current anode materials usually undergo large volumetric expansion and structural collapse during the charge-discharge process. Self-supporting carbon nanotubes encapsulated in sub-micro carbon fiber (SMCF@CNTs) are utilized as the KIB anode in this study. The SMCF@CNT anode exhibits high specific capacity, good rate performance, and cycling stability. The SMCF@CNT electrode has specific capacities of 236 mAh g-1 at 0.1 C and 108 mAh g-1 at 5 C and maintains over 193 mAh g-1 after 300 cycles at 1 C. Furthermore, a combined capacitive and diffusion-controlled K+ storage mechanism is proposed on the basis of the investigation using in situ Raman and quantitative analyses. By coupling the SMCF@CNT anode with the K0.3MnO2 cathode, a pouch cell with good flexibility delivers a capacity of 74.0 mAh g-1 at 20 mA g-1. This work is expected to promote the application of KIBs in wearable electronics.

Wet-Chemical Synthesis of Surface-Passivated Halide Perovskite Microwires for Improved Optoelectronic Performance and Stability.

One-dimensional (1D) halide perovskite materials with intrinsic high carrier mobility and long diffusion length hold great promises for high-performance optoelectronic devices, in which the passivation of the surface defects is of significance for further boosting its optoelectronic performance as well as its moisture stability. Herein, we demonstrate a simple room-temperature wet-chemical synthetic protocol for perovskite microwires with controlled morphologies and passivated surface states. This strategy allows for facile assembly of hydrophobic 1 H,1 H-perfluorooctylamine (PFA) molecules on the surface of the perovskite microwires owing to the coordination binding between the amino groups of PFA and Pb2+. Both steady and time-resolved photoluminescence measurements revealed that the passivation of PFA greatly benefit for the inhibition of the photogenerated carriers recombination. The constructed perovskite microwire-based photodetectors have shown increased detectivity of 4.99 × 1011 jones and responsivity of 1.27 A/W (light power density of 1 mW/cm2). Moreover, the hydrophobic fluorocarbon alkyl chains endow the perovskite microwires with higher resistance toward moisture. Such coating of a water-resisting layer resulted in greatly enhanced stability of perovskite microwires under the humidity of 55 ± 5% over 30 days. We thus believe that our work is of importance for the development of 1D halide perovskite photodetectors with highly improved performance and stability.