Compact Solid Electrolyte Interface Realization Employing Surface-Modified Fillers for Long-Lasting, High-Performance All-Solid-State Li-Metal Batteries.

The implementation of polymer-based Li-metal batteries is hindered by their low coulombic efficiency and poor cycling stability attributed to continuous electrolyte decomposition. Enhancement of the solid electrolyte interface (SEI) stability is key to mitigating electrolyte decomposition. This study proposes surface-functionalized silica mesoball fillers to fabricate a composite polymer electrolyte (MSBM-CPE). As a result of surface modification, the polyethylene oxide matrix benefits from the uniform distribution of the filler, which provides a large surface area and Lewis acid sites. Molecular dynamics simulations reveal that the dissociation energy of lithium bis(trifluoromethanesulfonyl)imide in the filler is fourfold higher (-1.95 eV) than that of the filler-free electrolyte. Consequently, the MSMB-CPE diffusivity is 30 times higher than its filler-free counterpart. The MSMB-CPE of ionic conductivity of 1.16 × 10-2 S cm-1 @60 °C and a venerable Li-ion transference number of 0.81. The excellent compatibility of MSMB-CPE with the Li anode is demonstrated by its stable symmetric cell performance under high current density (200 µA cm-2 @60 °C) for over 5000 h. Approximately 85.60% retention capacity of the [Li/MSMB-CPE/LiFePO4] full cell after 700 cycles. Furthermore, compositional analysis reveals that the SEI layer in MSMB-CPE is smooth with fewer by-products at the electrolyte/Li interface.

SABRE hyperpolarization of nicotinamide derivatives and their molecular dynamics properties.

Signal amplification by reversible exchange hyperpolarization explores the chemical structure and kinetic properties of nicotinamide derivatives. N-Benzyl nicotinamide and nicotinic acid hydrazide compounds display relatively fast dissociation rates of approximately 7-8 s-1 and long proton T1 relaxation times of 5-20 s, respectively. Consequently, these substrates exhibit remarkable signal enhancements, reaching approximately 175 and 102 fold, respectively, underscoring the efficacy of the hyperpolarization technique in elucidating the behavior of these compounds.

Complementary Hybrid Semiconducting Superlattices with Multiple Channels and Mutual Stabilization.

An organic-inorganic hybrid superlattice with near perfect synergistic integration of organic and inorganic constituents was developed to produce properties vastly superior to those of either moiety alone. The complementary hybrid superlattice is composed of multiple quantum wells of 4-mercaptophenol organic monolayers and amorphous ZnO nanolayers. Within the superlattice, multichannel formation was demonstrated at the organic-inorganic interfaces to produce an excellent-performance field effect transistor exhibiting outstanding field-effect mobility with band-like transport and steep subthreshold swing. Furthermore, mutual stabilizations between organic monolayers and ZnO effectively reduced the performance degradation notorious in exclusively organic and ZnO transistors.

A Robust Nonprecious CuFe Composite as a Highly Efficient Bifunctional Catalyst for Overall Electrochemical Water Splitting.

To generate hydrogen, which is a clean energy carrier, a combination of electrolysis and renewable energy sources is desirable. In particular, for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in electrolysis, it is necessary to develop nonprecious, efficient, and durable catalysts. A robust nonprecious copper-iron (CuFe) bimetallic composite is reported that can be used as a highly efficient bifunctional catalyst for overall water splitting in an alkaline medium. The catalyst exhibits outstanding OER and HER activity, and very low OER and HER overpotentials (218 and 158 mV, respectively) are necessary to attain a current density of 10 mA cm-2 . When used in a two-electrode water electrolyzer system for overall water splitting, it not only achieves high durability (even at a very high current density of 100 mA cm-2 ) but also reduces the potential required to split water into oxygen and hydrogen at 10 mA cm-2 to 1.64 V for 100 h of continuous operation.

Donor-Acceptor-Appended Triarylboron Lewis Acids: Ratiometric or Time-Resolved Turn-On Fluorescence Response toward Fluoride Binding.

Triarylboron Lewis acid compounds (CzmBoT (1c) and DPAmBoT (2c)), in which carbazole (Cz) or diphenylamine (DPA) donors are linked with a triazine acceptor in the ortho position of the phenylene ring are prepared and characterized. The treatment of 1c and 2c with the fluoride anion produces the corresponding fluoride adducts [1cF]- and [2cF]- as a tetraethylammonium salt. An X-ray diffraction study of [1cF]- reveals a twisted conformation between the Cz and phenylene rings. The Cz-containing 1c shows a ratiometric fluorescence change upon fluoride binding, while the DPA-containing 2c exhibits a turn-on fluorescence response in tetrahydrofuran. In particular, both fluoride adducts exhibit thermally activated delayed fluorescence (TADF) properties with microsecond-range lifetimes. Electrochemical and theoretical analysis suggests that the intramolecular charge-transfer transition from the donor to a conjugated acceptor fragment is switched to the donor to a triazine transition after fluoride binding. Theoretical analysis further demonstrates the twisted structure, effective highest occupied molecular orbital-lowest unoccupied molecular orbital separation, and the small energy splitting between the excited singlet and triplet states for the fluoride adducts, with all supporting the observed TADF. The time-resolved fluorescence measurements of 2c in the presence of both fluoride and a competitive fluorescent dye (Coumarin 6) effectively eliminate the short-lived fluorescence of a dye, retaining long-lived fluorescence signals originating only from [2cF]-.

Time Transient Electrochemical Monitoring of Tetraalkylammonium Polybromide Solid Particle Formation: Observation of Ionic Liquid-to-Solid Transitions.

Energy storage systems (ESSs) using a Br-/Br2 redox reaction such as a Zn/Br redox flow battery (RFB) or a redox-enhanced electrochemical capacitor (Redox-EC) suffer from self-discharge reactions resulting in significant Coulombic loss. To inhibit the self-discharge, quaternary ammonium (Q+) and tetraalkylammonium (T+) bromide are added to form ionic liquid (QBr2 n+1) and solid (TBr3) polybromides during the ESS charging process. The electrochemical formation of liquid QBr2 n+1 and its electrochemical properties have been examined. The detailed mechanisms of ionic solid TBr3 formation, however, have not yet been explored. In this article, we analyzed the ionic liquid-to-solid phase transition of TBr3 particles using a time transient electrochemical method. We suggest the formation of ionic solid TBr3 particles via hydrated TBr3 droplets as an intermediate phase, which are generated by electro-oxidation of Br- in an aqueous TBr solution. We found the phase transition time of TBr3 particles is strongly dependent on the chemical structure of T+ and the concentration of TBr in an aqueous solution.

Adjustable Intermolecular Interactions Allowing 2D Transition Metal Dichalcogenides with Prolonged Scavenging Activity for Reactive Oxygen Species.

There is an increasing demand for control over the dimensions and functions of transition metal dichalcogenides (TMDs) in aqueous solution toward biological and medical applications. Herein, an approach for the exfoliation and functionalization of TMDs in water via modulation of the hydrophobic interaction between poly(ε-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) and the basal planes of TMDs is reported. Decreasing the hydrophobic PCL length of PCL-b-PEG from 5000 g mol-1 (PCL5000 ) to 460 g mol-1 (PCL460 ) significantly increases the exfoliation efficiency of TMD nanosheets because the polymer-TMD hydrophobic interaction becomes dominant over the polymer-polymer interaction. The TMD nanosheets exfoliated by PCL460 -b-PEG5000 (460-WS2 , 460-WSe2 , 460-MoS2 , and 460-MoSe2 ) show excellent and prolonged scavenging activity for reactive oxygen species (ROS), but each type of TMD displays a different scavenging tendency against hydroxyl, superoxide, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals. A mechanistic study based on electron paramagnetic resonance spectroscopy and density functional theory simulations suggests that radical-mediated oxidation of TMDs and hydrogen transfer from the oxidized TMDs to radicals are crucial steps for ROS scavenging by TMD nanosheets. As-prepared 460-TMDs are able to effectively scavenge ROS in HaCaT human keratinocytes, and also exhibit excellent biocompatibility.

Nido-Carboranes: Donors for Thermally Activated Delayed Fluorescence.

An approach to the design of nido-carborane-based luminescent compounds that can exhibit thermally activated delayed fluorescence (TADF) is proposed. 7,8-Dicarba-nido-undecaboranes (nido-carboranes) having various 8-R groups (R=H, Me, i-Pr, Ph) are appended to the meta or para position of the phenyl ring of the dimesitylphenylborane (PhBMes2 ) acceptor, forming donor-acceptor compounds (nido-m1-m4 and nido-p1-p4). The bulky 8-R group and meta substitution of the nido-carborane are essential to attain a highly twisted arrangement between the donor and acceptor moieties, leading to a very small energy splitting between the singlet and triplet excited states (ΔEST <0.05 eV for nido-m2, -m3, and -p3). These compounds exhibit efficient TADF with microsecond-range lifetimes. In particular, nido-m2 and -m3 display aggregation-induced emission (AIE) with TADF properties.

Exploring Interfacial Events in Gold-Nanocluster-Sensitized Solar Cells: Insights into the Effects of the Cluster Size and Electrolyte on Solar Cell Performance.

Gold nanoclusters (Au NCs) with molecule-like behavior have emerged as a new light harvester in various energy conversion systems. Despite several important strides made recently, efforts toward the utilization of NCs as a light harvester have been primarily restricted to proving their potency and feasibility. In solar cell applications, ground-breaking research with a power conversion efficiency (PCE) of more than 2% has recently been reported. Because of the lack of complete characterization of metal cluster-sensitized solar cells (MCSSCs), however, comprehensive understanding of the interfacial events and limiting factors which dictate their performance remains elusive. In this regard, we provide deep insight into MCSSCs for the first time by performing in-depth electrochemical impedance spectroscopy (EIS) analysis combined with physical characterization and density functional theory (DFT) calculations of Au NCs. In particular, we focused on the effect of the size of the Au NCs and electrolytes on the performance of MCSSCs and reveal that they are significantly influential on important solar cell characteristics such as the light absorption capability, charge injection kinetics, interfacial charge recombination, and charge transport. Besides offering comprehensive insights, this work represents an important stepping stone toward the development of MCSSCs by accomplishing a new PCE record of 3.8%.

Aromatic cages B: unprecedented existence of octagonal holes in boron clusters.

The cage-like structures containing octagonal holes are located as the lowest-lying isomers for the B. The presence of octagonal holes, which have been found for the first time, not only gives us new insight into the bonding motif, but also marks a breakthrough in the structural characteristics of boron clusters since they were never expected to be stable units for elemental clusters. These cages are composed of both delocalized σ and π electron systems that consequently make them aromatic and thermodynamically stable.

Correction: Aromatic cages B42°/⁺: unprecedented existence of octagonal holes in boron clusters.

Correction for 'Aromatic cages B42(0/+): unprecedented existence of octagonal holes in boron clusters' by Truong Ba Tai et al., Phys. Chem. Chem. Phys., 2016, DOI: 10.1039/c5cp07342a.

Iridium Cyclometalates with Tethered o-Carboranes: Impact of Restricted Rotation of o-Carborane on Phosphorescence Efficiency.

Iridium(III) cyclometalates (1c and 2c) in which the two carborane units on the 4- or 5-positions of 2-phenylpyridine (ppy) ligands were tethered by an alkylene linker were prepared to investigate the effect of free rotation of o-carborane on phosphorescence efficiency. In comparison with the unlinked complex, tethering the o-carboranes to the 5-positions of ppy ligands (2c) enhanced phosphorescence efficiency by over 30-fold in polar medium (Φ(PL) = 0.37 vs 0.011 in THF), while restricting the rotation of o-carborane at the 4-positions (1c) negatively affected the phosphorescence efficiency. The different effects of restricted rotation of o-carborane on phosphorescence efficiency were likely a result of the different variations of the carboranyl C-C bond distances in the excited state.

Selective synthesis of ruthenium(II) Metalla[2]catenane via solvent and guest-dependent self-assembly.

The coordination-driven self-assembly of an anthracene-functionalized ditopic pyridyl donor and a tetracene-based dinuclear Ru(II) acceptor resulted in an interlocked metalla[2]catenane, [M2L2]2, in methanol and a corresponding monorectangle, [M2L2], in nitromethane. Subsequently, guest template, solvent, and concentration effects allowed the self-assembly to be reversibly fine-tuned among monorectangle and catenane structures.

Manipulation of phosphorescence efficiency of cyclometalated iridium complexes by substituted o-carboranes.

A series of [(C^N)2 Ir(acac)] complexes [{5-(2-R-CB)ppy}2 Ir(acac)] (3 a-3 g; acac=acetylacetonate, CB=o-carboran-1-yl, ppy=2-phenylpyridine; R=H (3 a), Me (3 b), iPr (3 c), iBu (3 d), Ph (3 e), CF3 C6 H4 (3 f), C6 F5 (3 g)) with various 2-R-substituted o-carboranes at the 5-position in the phenyl ring of the ppy ligand were prepared. X-ray diffraction studies revealed that the carboranyl CC bond length increases with increasing steric and electron-withdrawing effects from the 2-R substituents. Although the absorption and emission wavelengths of the complexes are almost invariant to the change of 2-R group, the phosphorescence quantum efficiency varies from highly emissive (ΦPL ≈0.80 for R=H, alkyl) to poorly emissive (R=aryl) depending on the 2-R group and the polarity of the medium. Theoretical studies suggest that 1) the almost nonemissive nature of the 2-aryl-substituted complexes is mainly attributable to the large contribution to the LUMO in the S1 excited state from an o-carborane unit and 2) the variation in the CC bond length between the S0 and T1 state structures increases with increasing steric (2-alkyl) and electronic effects (2-aryl) of the 2-R substituent and the polarity of the solvent. The solution-processed electroluminescence (EL) devices that incorporated 3 b and 3 d as emitters displayed higher performance than the device based on the parent [(ppy)2 Ir(acac)] complex. Along with the high phosphorescence efficiency, the bulkiness of the 2-R-o-carborane unit is shown to play an important role in improving device performance.

Two Dimensional Aggregation Behaviors of Quinoxaline Dendrimers.

This study focuses on the molecular behavior of two dendrimers containing a hydrophilic core group (carboxyl group) and hydrophobic branches (quinoxaline and methoxyphenyl groups), 2,3-bis(4-(2,3- bis(4-methoxyphenyl)quinoxalin-6-yloxy)phenyl)quinoxaline-6-carb-oxylic acid (G2) and 2,3-bis(4-(2,3-bis(4-(2,3-bis(4-methoxyphenyl)quinoxalin-6-yloxy)phe-nyl)quinoxalin-6-y-oxy)phenyl) quin oxaline-6-carboxylic acid (G3) at the air-water interface. To understand the mechanism of the self-assembly of these molecules, we measured the surface pressure-area (III-A) isotherm and investigated the surface morphology of Langmuir-Blodgett films transferred onto hydrophilic silicon wafers using atomic force microscopy (AFM). Upon compression, G2 molecules stand up and steadily make close-packed monolayer whereas G3 molecules form circular domains and gradually make aggregates of domains. These results were confirmed by the X-ray Reflectivity (XRR) profiles of G2 and G3 monolayers transferred onto silicon substrates.

Doubling the capacity of lithium manganese oxide spinel by a flexible skinny graphitic layer.

By coating nanoparticular lithium manganese oxide (LMO) spinel with a few layers of graphitic basal planes, the capacity of the material reached up to 220 mA h g(-1) at a cutoff voltage of 2.5 V. The graphitic layers 1) provided a facile electron-transfer highway without hindering ion access and, more interestingly, 2) stabilized the structural distortion at the 3 V region reaction. The gain was won by a simple method in which microsized LMO was ball-milled in the presence of graphite with high energy. Vibratory ball milling pulverized the LMO into the nanoscale, exfoliated graphite of less than 10 layers and combined them together with an extremely intimate contact. Ab initio calculations show that the intrinsically very low electrical conductivity of the tetragonal phase of the LMO is responsible for the poor electrochemical performance in the 3 V region and could be overcome by the graphitic skin strategy proposed.

Remnant Copper Cation-Assisted Atom Mixing in Multicomponent Nanoparticles.

Nanostructured high-/medium-entropy compounds have emerged as important catalytic materials for energy conversion technologies, but complex thermodynamic relationships involved with the element mixing enthalpy have been a considerable roadblock to the formation of stable single-phase structures. Cation exchange reactions (CERs), in particular with copper sulfide templates, have been extensively investigated for the synthesis of multicomponent heteronanoparticles with unconventional structural features. Because copper cations within the host copper sulfide templates are stoichiometrically released with incoming foreign cations in CERs to maintain the overall charge balance, the complete absence of Cu cations in the nanocrystals after initial CERs would mean that further compositional variation would not be possible by subsequent CERs. Herin, we successfully retained a portion of Cu cations within the silver sulfide (Ag2S) and gold sulfide (Au2S) phases of Janus Cu2-xS-M2S (M = Ag, Au) nanocrystals after the CERs, by partially suppressing the transformation of the anion sublattice that inevitably occurs during the introduction of external cations. Interestingly, the subsequent CERs on Janus Cu1.81S-M2S (M = Ag, Au), by utilizing the remnant Cu cations, allowed the construction of Janus Cu1.81S-AgxAuyS, which preserved the initial heterointerface. The synthetic strategy described in this work to suppress the complete removal of the Cu cation from the template could fabricate the CER-driven heterostructures with greatly diversified compositions, which exhibit unusual optical and catalytic properties.

Scaling-Up Insights for Zinc-Air Battery Technologies Realizing Reversible Zinc Anodes.

Zinc-air battery (ZAB) technology is considered one of the promising candidates to complement the existing lithium-ion batteries for future large-scale high-energy-storage demands. The scientific literature reveals many efforts for the ZAB chemistries, materials design, and limited accounts for cell design principles with apparently superior performances for liquid and solid-state electrolytes. However, along with the difficulty of forming robust solid-electrolyte interphases, the discrepancy in testing methods and assessment metrics severely challenges the realistic evaluation/comparison and commercialization of ZABs. Here, strategies to formulate reversible zinc anodes are proposed and specific cell-level energy metrics (100-500 Wh kg-1 ) and realistic long-cycling operations are realized. Stabilizing anode/electrolyte interfaces results in a cumulative capacity of 25 Ah cm-2 and Coulomb efficiency of >99.9% for 5000 plating/stripping cycles. Using 1-10 Ah scale (≈500 Wh kg-1 at cell level) solid-state zinc-air pouch cells, scale-up insights for Ah-level ZABs that can progress from lab-scale research to practical production are also offered.

NbO2 a Highly Stable, Ultrafast Anode Material for Li- and Na-Ion Batteries.

Anode materials with fast charging capabilities and stability are critical for realizing next-generation Li-ion batteries (LIBs) and Na-ion batteries (SIBs). The present work employs a simple synthetic strategy to obtain NbO2 and studies its applications as an anode for LIB and SIB. In the case of the LIB, it exhibited a specific capacity of 344 mAh g-1 at 100 mA g-1. It also demonstrated remarkable stability over 1000 cycles, with 92% capacity retention. Additionally, it showed a unique fast charging capability, which takes 30 s to reach a specific capacity of 83 mAh g-1. For the SIB, NbO2 exhibited a specific capacity of 244 mAh g-1 at 50 mA g-1 and showed 70% capacity retention after 500 cycles. Furthermore, detailed density functional theory reveals that various factors like bulk and surface charging processes, lower ion diffusion energy barriers, and superior electronic conductivity of NbO2 are responsible for the observed battery performances.

An Ion-Channel-Restructured Zwitterionic Covalent Organic Framework Solid Electrolyte for All-Solid-State Lithium-Metal Batteries.

Organic solid electrolytes offer an effective route for safe and high-energy-density all-solid-state Li metal batteries. However, it remains a challenge to devise a new strategy to promote the dissociation of strong ion pairs and the transport of ionic components in organic solid electrolytes. Herein, a zwitterionic covalent organic framework (Zwitt-COF) with well-defined chemical and pore structures is prepared as a solid electrolyte capable of accelerating the dissociation and transport of Li ions. The Zwitt-COF solid electrolyte exhibits a high room-temperature ionic conductivity of 1.65 × 10-4  S cm-1 with a wide electrochemical stability window. Besides, the Zwitt-COF solid electrolyte displays stable Li plating/stripping behavior via effective inhibition of the formation of Li dendrites and dead Li, leading to superior long-term cycle performance with retention of 99% discharge capacity and 98% Coulombic efficiency in an all-solid-state Li-metal battery. Theoretical simulations reveal that the incorporation of zwitterionic groups into COF can facilitate the dissociation of strong ion pairs and reconstruct the AA-stacking configuration by dissociative adsorption of Li+ ions on Zwitt-COF producing linear hexagonal ion channels in the Zwitt-COF solid electrolyte. This strategy based on Zwitt-COF can provide an alternative way to construct various solid-state Li batteries.