Activating reversible carbonate reactions in Nasicon solid electrolyte-based Na-air battery via in-situ formed catholyte.

Out of practicality, ambient air rather than oxygen is preferred as a fuel in electrochemical systems, but CO2 and H2O present in air cause severe irreversible reactions, such as the formation of carbonates and hydroxides, which typically degrades performance. Herein, we report on a Na-air battery enabled by a reversible carbonate reaction (Na2CO3·xH2O, x = 0 or 1) in Nasicon solid electrolyte (Na3Zr2Si2PO12) that delivers a much higher discharge potential of 3.4 V than other metal-air batteries resulting in high energy density and achieves > 86 % energy efficiency at 0.1 mA cm-2 over 100 cycles. This cell design takes advantage of moisture in ambient air to form an in-situ catholyte via the deliquescent property of NaOH. As a result, not only reversible electrochemical reaction of Na2CO3·xH2O is activated but also its kinetics is facilitated. Our results demonstrate the reversible use of free ambient air as a fuel, enabled by the reversible electrochemical reaction of carbonates with a solid electrolyte.

Photo-Assisted Ferroelectric Domain Control for α-In2 Se3 Artificial Synapses Inspired by Spontaneous Internal Electric Fields.

α-In2 Se3 semiconductor crystals realize artificial synapses by tuning in-plane and out-of-plane ferroelectricity with diverse avenues of electrical and optical pulses. While the electrically induced ferroelectricity of α-In2 Se3 shows synaptic memory operation, the optically assisted synaptic plasticity in α-In2 Se3 has also been preferred for polarization flipping enhancement. Here, the synaptic memory behavior of α-In2 Se3 is demonstrated by applying electrical gate voltages under white light. As a result, the induced internal electric field is identified at a polarization flipped conductance channel in α-In2 Se3 /hexagonal boron nitride (hBN) heterostructure ferroelectric field effect transistors (FeFETs) under white light and discuss the contribution of this built-in electric field on synapse characterization. The biased dipoles in α-In2 Se3 toward potentiation polarization direction by an enhanced internal built-in electric field under illumination of white light lead to improvement of linearity for long-term depression curves with proper electric spikes. Consequently, upon applying appropriate electric spikes to α-In2 Se3 /hBN FeFETs with illuminating white light, the recognition accuracy values significantly through the artificial learning simulation is elevated for discriminating hand-written digit number images.

Gradient Lithium Metal Infusion in Ag-Decorated Carbon Fibers for High-Capacity Lithium Metal Battery Anodes.

Lithium (Li) metal is a promising anode material for high-energy-density Li batteries due to its high specific capacity. However, the uneven deposition of Li metal causes significant volume expansion and safety concerns. Here, we investigate the impact of a gradient-infused Li-metal anode using silver (Ag)-decorated carbonized cellulose fibers (Ag@CC) as a three-dimensional (3D) current collector. The loading level of the gradient-infused Li-metal anode is controlled by the thermal infusion time of molten Li. In particular, a 5 s infusion time in the Ag@CC current collector creates an appropriate space with a lithiophilic surface, resulting in improved cycling stability and a reduced volume expansion rate. Moreover, integrating a 5 s Ag@CC anode with a high-capacity cathode demonstrates superior electrochemical performance with minimal volume expansion. This suggests that a gradient-infused Li-metal anode using Ag@CC as a 3D current collector represents a novel design strategy for Li-metal-based high-capacity Li-ion batteries.

Reversible Na Plating/Stripping with High Areal Capacity Using an Electroconductive Liquid Electrolyte System.

Anode-free sodium-metal batteries (AFSMBs) are promising candidates for maximizing energy density and minimizing cost and safety hazards in the absence of metallic sodium during cell assembly. The practical implementation of AFSMBs is hindered by the low cycling stability of Na-metal plating and stripping, particularly under high areal capacities, due to unstable solid electrolyte interphase (SEI) layer formation with electrolyte decomposition and inactive dead Na formation. Here, we proposed an electroconductive electrolyte system consisting of liquid electrolytes that accept electrons at a certain energy level and form electronically conductive and solid electrolytes that prevent internal short circuit through low electronic conductivity. The electron acceptability and high electronic conductivity of the liquid electrolyte can suppress the irreversible electron transfer with electrolyte decomposition and reutilize the inactive dead metal, respectively. The functions of the system were demonstrated using a sodium biphenyl liquid electrolyte-NASICON solid electrolyte in a seawater battery (SWB) system, which features an infinite sodium source. The anode-free SWB cells achieved a high Coulombic efficiency of ≥99.9% for over 60 cycles at a high areal capacity of ∼24 mAh/cm2. This study provides insight into the Na plating/stripping properties in anode-free systems and proposes a significant strategy for improving the reversibility of metal anodes for various battery systems with solid electrolytes.

Acid- and Gas-Scavenging Electrolyte Additive Improving the Electrochemical Reversibility of Ni-Rich Cathodes in Li-Ion Batteries.

In view of their high theoretical capacities, nickel-rich layered oxides are promising cathode materials for high-energy Li-ion batteries. However, the practical applications of these oxides are hindered by transition metal dissolution, microcracking, and gas/reactive compound formation due to the undesired reactions of residual lithium species. Herein, we show that the interfacial degradation of the LiNi0.9CoxMnyAlzO2 (NCMA, x + y + z = 0.1) cathode and the graphite (Gr) anode of a representative Li-ion battery by HF can be hindered by supplementing the electrolyte with tert-butyldimethylsilyl glycidyl ether (tBS-GE). The silyl ether moiety of tBS-GE scavenges HF and PF5, thus stabilizing the interfacial layers on both electrodes, while the epoxide moiety reacts with CO2 released by the parasitic reaction between HF and Li2CO3 on the NCMA surface to afford cyclic carbonates and thus suppresses battery swelling. NCMA/Gr full cells fabricated by supplementing the baseline electrolyte with 0.1 wt % tBS-GE feature an increased capacity retention of 85.5% and deliver a high discharge capacity of 162.9 mAh/g after 500 cycles at 1 C and 25 °C. Thus, our results reveal that the molecular aspect-based design of electrolyte additives can be efficiently used to eliminate reactive species and gas components from Li-ion batteries and increase their performance.

Nanocomposite Engineering of a High-Capacity Partially Ordered Cathode for Li-Ion Batteries.

Understanding the local cation order in the crystal structure and its correlation with electrochemical performances has advanced the development of high-energy Mn-rich cathode materials for Li-ion batteries, notably Li- and Mn-rich layered cathodes (LMR, e.g., Li1.2 Ni0.13 Mn0.54 Co0.13 O2 ) that are considered as nanocomposite layered materials with C2/m Li2 MnO3 -type medium-range order (MRO). Moreover, the Li-transport rate in high-capacity Mn-based disordered rock-salt (DRX) cathodes (e.g., Li1.2 Mn0.4 Ti0.4 O2 ) is found to be influenced by the short-range order of cations, underlining the importance of engineering the local cation order in designing high-energy materials. Herein, the nanocomposite is revealed, with a heterogeneous nature (like MRO found in LMR) of ultrahigh-capacity partially ordered cathodes (e.g., Li1.68 Mn1.6 O3.7 F0.3 ) made of distinct domains of spinel-, DRX- and layered-like phases, contrary to conventional single-phase DRX cathodes. This multi-scale understanding of ordering informs engineering the nanocomposite material via Ti doping, altering the intra-particle characteristics to increase the content of the rock-salt phase and heterogeneity within a particle. This strategy markedly improves the reversibility of both Mn- and O-redox processes to enhance the cycling stability of the partially ordered DRX cathodes (nearly ≈30% improvement of capacity retention). This work sheds light on the importance of nanocomposite engineering to develop ultrahigh-performance, low-cost Li-ion cathode materials.

Sacrificial Catalyst of Carbothermal-Shock-Synthesized 1T-MoS2 Layers for Ultralong-Lifespan Seawater Battery.

A Pt-nanoparticle-decorated 1T-MoS2 layer is designed as a sacrificial electrocatalyst by carbothermal shock (CTS) treatment to improve the energy efficiency and lifespan of seawater batteries. The phase transition of MoS2 crystals from 2H to metallic 1T─induced by the simple but potent CTS treatment─improves the oxygen-reduction-reaction (ORR) activity in seawater catholyte. In particular, the MoS2-based sacrificial catalyst effectively decreases the overpotential during charging via edge oxidation of MoS2, enhancing the cycling stability of the seawater battery. Furthermore, Pt nanoparticles are deposited onto CTS-MoS2 via an additional CTS treatment. The resulting specimen exhibits a significantly low charge/discharge potential gap of Δ0.39 V, high power density of 6.56 mW cm-2, and remarkable cycling stability up to ∼200 cycles (∼800 h). Thus, the novel strategy reported herein for the preparation of Pt-decorated 1T-MoS2 by CTS treatment could facilitate the development of efficient bifunctional electrocatalysts for fabricating seawater batteries with long service life.

Photoswitchable Microgels for Dynamic Macrophage Modulation.

Dynamic manipulation of supramolecular self-assembled structures is achieved irreversibly or under non-physiological conditions, thereby limiting their biomedical, environmental, and catalysis applicability. In this study, microgels composed of azobenzene derivatives stacked via π-cation and π-π interactions are developed that are electrostatically stabilized with Arg-Gly-Asp (RGD)-bearing anionic polymers. Lateral swelling of RGD-bearing microgels occurs via cis-azobenzene formation mediated by near-infrared-light-upconverted ultraviolet light, which disrupts intermolecular interactions on the visible-light-absorbing upconversion-nanoparticle-coated materials. Real-time imaging and molecular dynamics simulations demonstrate the deswelling of RGD-bearing microgels via visible-light-mediated trans-azobenzene formation. Near-infrared light can induce in situ swelling of RGD-bearing microgels to increase RGD availability and trigger release of loaded interleukin-4, which facilitates the adhesion structure assembly linked with pro-regenerative polarization of host macrophages. In contrast, visible light can induce deswelling of RGD-bearing microgels to decrease RGD availability that suppresses macrophage adhesion that yields pro-inflammatory polarization. These microgels exhibit high stability and non-toxicity. Versatile use of ligands and protein delivery can offer cytocompatible and photoswitchable manipulability of diverse host cells.

Amphi-Active Superoxide-Solvating Charge Redox Mediator for Highly Stable Lithium-Oxygen Batteries.

A multifunctional electrolyte additive for lithium oxygen batteries (LOBs) was designed to have (1) a redox-active moiety to mediate decomposition of lithium peroxide (Li2O2 as the final discharge product) during charging and (2) a solvent moiety to solvate and stabilize lithium superoxide (LiO2 as the intermediate discharge product) in electrolyte during discharging. 4-Acetamido-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidin-1-yl)oxyl) or AAT was employed as the additive working for both charge and discharge processes (amphi-active). The redox-active moiety was rooted in TEMPO, while the acetamido (AA) functional group inherited the high donor number (DN) of N,N-dimethylacetamide (DMAc). Integrating two functional moieties (TEMPO and AA) into a single molecule resulted in the bifunctionality of AAT (1) facilitating Li2O2 decomposition by the TEMPO moiety and (2) encouraging the solvent mechanism of Li2O2 formation by the high-DN AA moiety. Significantly improved LOB performances were achieved by the superoxide-solvating charge redox mediator, which were not obtained by a simple cocktail of TEMPO and DMAc.

Gate-Tuned Gas Molecule Sensitivity of a Two-Dimensional Semiconductor.

In this work, we develop a gate-tunable gas sensor based on a MoS2/hBN heterostructure field effect transistor. Through experimental measurements and numerical simulations, we systematically reveal a principle that relates the concentration of the target gas and sensing signals (ΔI/I0) as a function of gate bias. Because a linear relationship between ΔI/I0 and the gas concentration guarantees reliable sensor operation, the optimal gate bias condition for linearity was investigated. Taking NO2 and NH3 as target molecules, it is clarified that the bias condition greatly depends on the electron accepting/donating nature of the gas. The effects of the bandgap and polarity of the transition metal dichalcogenides (TMDC) channel are also discussed. In order to achieve linearly increasing signals that are stable with respect to the gas concentration, a sufficiently large VBG within VBG > 0 is required. We expect this work will shed light on a way to precisely design reliable semiconducting gas sensors based on the characteristics of TMDC and target gas molecules.

Rapid access to polycyclic N-heteroarenes from unactivated, simple azines via a base-promoted Minisci-type annulation.

Conventional synthetic methods to yield polycyclic heteroarenes have largely relied on metal-mediated arylation reactions requiring pre-functionalised substrates. However, the functionalisation of unactivated azines has been restricted because of their intrinsic low reactivity. Herein, we report a transition-metal-free, radical relay π-extension approach to produce N-doped polycyclic aromatic compounds directly from simple azines and cyclic iodonium salts. Mechanistic and electron paramagnetic resonance studies provide evidence for the in situ generation of organic electron donors, while chemical trapping and electrochemical experiments implicate an iodanyl radical intermediate serving as a formal biaryl radical equivalent. This intermediate, formed by one-electron reduction of the cyclic iodonium salt, acts as the key intermediate driving the Minisci-type arylation reaction. The synthetic utility of this radical-based annulative π-extension method is highlighted by the preparation of an N-doped heptacyclic nanographene fragment through fourfold C-H arylation.

Coupling structural evolution and oxygen-redox electrochemistry in layered transition metal oxides.

Lattice oxygen redox offers an unexplored way to access superior electrochemical properties of transition metal oxides (TMOs) for rechargeable batteries. However, the reaction is often accompanied by unfavourable structural transformations and persistent electrochemical degradation, thereby precluding the practical application of this strategy. Here we explore the close interplay between the local structural change and oxygen electrochemistry during short- and long-term battery operation for layered TMOs. The substantially distinct evolution of the oxygen-redox activity and reversibility are demonstrated to stem from the different cation-migration mechanisms during the dynamic de/intercalation process. We show that the π stabilization on the oxygen oxidation initially aids in the reversibility of the oxygen redox and is predominant in the absence of cation migrations; however, the π-interacting oxygen is gradually replaced by σ-interacting oxygen that triggers the formation of O-O dimers and structural destabilization as cycling progresses. More importantly, it is revealed that the distinct cation-migration paths available in the layered TMOs govern the conversion kinetics from π to σ interactions. These findings constitute a step forward in unravelling the correlation between the local structural evolution and the reversibility of oxygen electrochemistry and provide guidance for further development of oxygen-redox layered electrode materials.

Critical Void Dimension of Carbon Frameworks to Accommodate Insoluble Products of Lithium-Oxygen Batteries.

High-energy density lithium-oxygen batteries (LOBs) seriously suffer from poor rate capability and cyclability due to the slow oxygen-related electrochemistry and uncontrollable formation of lithium peroxide (Li2O2) as an insoluble discharge product. In this work, we accommodated the discharge product in macro-scale voids of a carbon-framed architecture with meso-dimensional channels on the carbon frame and open holes connecting the neighboring voids. More importantly, we found that a specific dimension of the voids guaranteed high capacity and cycling durability of LOBs. The best LOB performances were achieved by employing the carbon-framed architecture having voids of 0.8 µm size as the cathode of the LOB when compared with the cathodes having voids of 0.3 and 1.4 µm size. The optimized void size of 0.8 µm allowed only a monolithic integrity of lithium peroxide deposit within a void during discharging. The deposit was grown to be a yarn ball-looking sphere exactly fitting the shape and size of the void. The good electric contact allowed the discharge product to be completely decomposed during charging. On the other hand, the void space was not fully utilized due to the mass transfer pathway blockage at the sub-optimized 0.3 µm and the formation of multiple deposit integrities within a void at the sur-optimized 1.4 µm. Consequently, the critical void dimension at 0.8 µm was superior to other dimensions in terms of the void space utilization efficiency and the lithium peroxide decomposition efficiency, disallowing empty space and side reactions during discharging.

Synthesis of α,ß-unsaturated ketones through nickel-catalysed aldehyde-free hydroacylation of alkynes.

α,ß-Unsaturated ketones are common feedstocks for the synthesis of fine chemicals, pharmaceuticals, and natural products. Transition metal-catalysed hydroacylation reactions of alkynes using aldehydes have been recognised as an atom-economical route to access α,ß-unsaturated ketones through chemoselective aldehydic C-H activation. However, the previously reported hydroacylation reactions using rhodium, cobalt, or ruthenium catalysts require chelating moiety-bearing aldehydes to prevent decarbonylation of acyl-metal-hydride complexes. Herein, we report a nickel-catalysed anti-Markovnikov selective coupling process to afford non-tethered E-enones from terminal alkynes and S-2-pyridyl thioesters in the presence of zinc metal as a reducing agent. Utilization of a readily available thioester as an acylating agent and water as a proton donor enables the mechanistically distinctive and aldehyde-free hydroacylation of terminal alkynes. This non-chelation-controlled approach features mild reaction conditions, high step economy, and excellent regio- and stereoselectivity.

Nitrate Molten Salt Electrolytes with Iron Oxide Catalysts for Open and Sealed Li-O2 Batteries.

Li-O2 batteries with nitrate molten salt electrolytes are attracting considerable attention owing to their various electrochemical pathways to form a discharge product upon the open and sealed systems. Here, we investigate nitrate molten salt electrolyte-based open and sealed Li-O2 batteries with pristine and iron oxide catalysts. Through the systematic analysis of various Li-O2 battery characteristics, we observe the irreversible electrochemical reactions of the open Li-O2 battery with an iron oxide catalyst that erodes the battery performance due to the detrimental parasitic reaction of H2 gas evolution from the Li anode. In contrast, the sealed Li-O2 system with cathodes containing the iron oxide catalyst exhibits the formation and decomposition of Li2O discharge products without significant side reactions, which guarantees long cycle endurance, high-rate performance, and a gravimetric energy density. Thus, promising electrochemical results from the sealed Li-O2 system with the iron oxide catalyst provide a viable strategy for the high-performance molten salt-based Li-O2 battery.

Metal-Ion Chelating Gel Polymer Electrolyte for Ni-Rich Layered Cathode Materials at a High Voltage and an Elevated Temperature.

Nickel-rich layered oxides (LiNi1-x-yCoxMnyO2; (1 - x - y) ≥ 0.6), the high-energy-density cathode materials of lithium-ion batteries (LIBs), are seriously unstable at voltages higher than 4.5 V versus Li/Li+ and temperatures higher than 50 °C. Herein, we demonstrated that the failure mechanism of a nickel-rich layered oxide (LiNi0.6Co0.2Mn0.2O2) behind the instability was successfully suppressed by employing cyanoethyl poly(vinyl alcohol) having pyrrolidone moieties (Pyrd-PVA-CN) as a metal-ion-chelating gel polymer electrolyte (GPE). The metal-ion-chelating GPE blocked the plating of transition-metal ions dissolved from the cathode by capturing the ions (anode protection). High-concentration metal-ion environments developed around the cathode surface by the GPE suppressed the irreversible phase transition of the cathode material from the layered structure to the rock-salt structure (cathode protection). Resultantly, the capacity retention was significantly improved at a high voltage and a high temperature. Capacity retention and coulombic efficiency of a full-cell configuration of a nickel-rich layered oxide with graphite were significantly improved in the presence of the GPE especially at a high cutoff voltage (4.4 V) and an elevated temperature (55 °C).

Alkali-Metal-Mediated Reversible Chemical Hydrogen Storage Using Seawater.

The economic viability and systemic sustainability of a green hydrogen economy are primarily dependent on its storage. However, none of the current hydrogen storage methods meet all the targets set by the US Department of Energy (DoE) for mobile hydrogen storage. One of the most promising routes is through the chemical reaction of alkali metals with water; however, this method has not received much attention owing to its irreversible nature. Herein, we present a reconditioned seawater battery-assisted hydrogen storage system that can provide a solution to the irreversible nature of alkali-metal-based hydrogen storage. We show that this system can also be applied to relatively lighter alkali metals such as lithium as well as sodium, which increases the possibility of fulfilling the DoE target. Furthermore, we found that small (1.75 cm2) and scaled-up (70 cm2) systems showed high Faradaic efficiencies of over 94%, even in the presence of oxygen, which enhances their viability.

Ordered Mesoporous Carbons with Graphitic Tubular Frameworks by Dual Templating for Efficient Electrocatalysis and Energy Storage.

Ordered mesoporous carbons (OMCs) have attracted considerable interest owing to their broad utility. OMCs reported to date comprise amorphous rod-like or tubular or graphitic rod-like frameworks, which exhibit tradeoffs between conductivity and surface area. Here we report ordered mesoporous carbons constructed with graphitic tubular frameworks (OMGCs) with tunable pore sizes and mesostructures via dual templating, using mesoporous silica and molybdenum carbide as exo- and endo-templates, respectively. OMGCs simultaneously realize high electrical conductivity and large surface area and pore volume. Benefitting from these features, Ru nanoparticles (NPs) supported on OMGC exhibit superior catalytic activity for alkaline hydrogen evolution reaction and single-cell performance for anion exchange membrane water electrolysis compared to Ru NPs on other OMCs and commercial catalysts. Further, the OMGC-based full-carbon symmetric cell demonstrates excellent performances for Li-ion capacitors.

Enhancing the conductivity of PEDOT:PSS films for biomedical applications via hydrothermal treatment.

This paper reports a new biocompatible conductivity enhancement of poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) films for biomedical applications. Conductivity of PEDOT:PSS layer was reproducibly from 0.495 to 125.367 S cm-1 by hydrothermal (HT) treatment. The HT treatment employs water (relative humidity > 80%) and heat (temperature > 61 °C) instead of organic solvent doping and post-treatments, which can leave undesirable residue. The treatment can be performed using the sterilizing conditions of an autoclave. Additionally, it is possible to simultaneously reduce the electrical resistance, and sterilize the electrode for practical use. The key to conductivity enhancement was the structural rearrangement of PEDOT:PSS, which was determined using atomic force microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible spectroscopy. It was found that PEDOT inter-bridging occurred as a result of the structural rearrangement. Therefore, the conductivity increased on account of the continuous conductive pathways of the PEDOT chains. To test the biocompatible enhancement technique for biomedical applications, certain demonstrations, such as the monitoring of joint movements and skin temperature, and measuring electrocardiogram signals were conducted with the hydrothermal-treated PEDOT:PSS electrode. This simple, biocompatible treatment exhibited significant potential for use in other biomedical applications as well.

Tailored Poly(vinylidene fluoride-co-trifluoroethylene) Crystal Orientation for a Triboelectric Nanogenerator through Epitaxial Growth on a Chitin Nanofiber Film.

Tailoring the crystal orientation of poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) has attracted widespread interest because of its effects on the ferroelectric properties required for various electronic devices. In this study, we investigated the epitaxial growth of PVDF-TrFE on a chitin film for developing triboelectric nanogenerators (TENGs). The crystallographic match between the chitin and PVDF-TrFE enables the development of the intended crystal orientation, with the PVDF-TrFE polarization axis aligned perpendicular to the substrate. In addition, the epitaxially grown PVDF-TrFE on chitin not only enhances the performance of the TENG but also increases the stability of the hygroscopic chitin film against water. The corresponding TENG exhibits a significantly higher output current compared to that of a nonepitaxial PVDF-TrFE/chitin film. Furthermore, the triboelectric sensors based on epitaxial PVDF-TrFE/chitin films allow the monitoring of subtle pressures, suggesting that tailoring the crystal orientation of PVDF-TrFE is a promising approach for developing high-performance TENGs.