Semicrystalline IrOx with Abundant Boundaries for Overall Water Splitting.

Inorganic compounds with different crystalline and amorphous states may show distinct properties in catalytic applications. In this work, we control the crystallization level by fine thermal treatment and synthesize a semicrystalline IrOx material with the formation of abundant boundaries. Theoretical calculation reveals that the interfacial iridium with a high degree of unsaturation is highly active for the hydrogen evolution reaction compared to individual counterparts based on the optimal binding energy with hydrogen (H*). At the heat treatment temperature of 500 °C, the obtained IrOx-500 catalyst has dramatically promoted hydrogen evolution kinetics, endowing the iridium catalyst with a bifunctional activity for acidic overall water splitting with a total voltage of only 1.554 V at a current density of 10 mA cm-2. In light of the remarkable boundary-enhanced catalysis effects, the semicrystalline material should be further developed for other applications.

Guiding Uniform Li Plating/Stripping through Lithium-Aluminum Alloying Medium for Long-Life Li Metal Batteries.

The uncontrolled growth of Li dendrites upon cycling might result in low coulombic efficiency and severe safety hazards. Herein, a lithiophilic binary lithium-aluminum alloy layer, which was generated through an in situ electrochemical process, was utilized to guide the uniform metallic Li nucleation and growth, free from the formation of dendrites. Moreover, the formed LiAl alloy layer can function as a Li reservoir to compensate the irreversible Li loss, enabling long-term stability. The protected Li electrode shows superior cycling over 1700 h in a Li|Li symmetric cell.

Designing Air-Stable O3-Type Cathode Materials by Combined Structure Modulation for Na-Ion Batteries.

As promising high-capacity cathode materials for Na-ion batteries, O3-type Na-based metal oxides always suffer from their poor air stability originating from the spontaneous extraction of Na and oxidation of transition metals when exposed to air. Herein, a combined structure modulation is proposed to tackle concurrently the two handicaps via reducing Na layers spacing and simultaneously increasing valence state of transition metals. Guided by density functional theory calculations, we demonstrate such a modulation can be subtly realized through cosubstitution of one kind of heteroatom with comparable electronegativity and another one with substantially different Fermi level, by adjusting the structure of NaNi0.5Mn0.5O2 via Cu/Ti codoping. The as-obtained NaNi0.45Cu0.05Mn0.4Ti0.1O2 exhibits an increase of 20 times in stable air-exposure period and 9 times in capacity retention after 500 cycles, and even retains its structure and capacity after being soaked in water. Such a simple and effective structure modulation reveals a new avenue for high-performance O3-type cathodes and pushes the large-scale industrialization of Na-ion batteries a decisive step forward.

Rechargeable dual-metal-ion batteries for advanced energy storage.

Energy storage devices are more important today than any time before in human history due to the increasing demand for clean and sustainable energy. Rechargeable batteries are emerging as the most efficient energy storage technology for a wide range of portable devices, grids and electronic vehicles. Future generations of batteries are required to have high gravimetric and volumetric energy, high power density, low price, long cycle life, high safety and low self-discharge properties. However, it is quite challenging to achieve the above properties simultaneously in state-of-the-art single metal ion batteries (e.g. Li-ion batteries, Na-ion batteries and Mg-ion batteries). In this contribution, hybrid-ion batteries in which various metal ions simultaneously engage to store energy are shown to provide a new perspective towards advanced energy storage: by connecting the respective advantages of different metal ion batteries they have recently attracted widespread attention due to their novel performances. The properties of hybrid-ion batteries are not simply the superposition of the performances of single ion batteries. To enable a distinct description, we only focus on dual-metal-ion batteries in this article, for which the design and the benefits are briefly discussed. We enumerate some new results about dual-metal-ion batteries and demonstrate the mechanism for improving performance based on knowledge from the literature and experiments. Although the search for hybrid-ion batteries is still at an early age, we believe that this strategy would be an excellent choice for breaking the inherent disadvantages of single ion batteries in the near future.

Improving the electrochemical performance of the li4 ti5 o12 electrode in a rechargeable magnesium battery by lithium-magnesium co-intercalation.

Rechargeable magnesium batteries have attracted recent research attention because of abundant raw materials and their relatively low-price and high-safety characteristics. However, the sluggish kinetics of the intercalated Mg(2+) ions in the electrode materials originates from the high polarizing ability of the Mg(2+) ion and hinders its electrochemical properties. Here we report a facile approach to improve the electrochemical energy storage capability of the Li4 Ti5 O12 electrode in a Mg battery system by the synergy between Mg(2+) and Li(+) ions. By tuning the hybrid electrolyte of Mg(2+) and Li(+) ions, both the reversible capacity and the kinetic properties of large Li4 Ti5 O12 nanoparticles attain remarkable improvement.

A single-beam NIR laser-triggered full-color upconversion tuning of a Er/Tm:CsYb2F7@glass photothermal nanocomposite for optical security.

The development of advanced luminescent materials is highly desirable for addressing the rising threat of forgery. However, it is challenging to achieve stable full-color upconversion (UC) tuning in the same matrix upon a single-beam light excitation so as to ensure that authentic items are irreproducible. Herein, hexagonal Er/Tm:CsYb2F7 nanocrystals (NCs) embedded inorganic glass via an in situ crystallization strategy is fabricated, which can emit blue, cyan, green, yellow, orange, red and near-infrared (NIR) UC emissions by simply modifying an incident 980 nm laser power. This UC tuning is attributed to the combination roles of the highly efficient laser-induced photothermal effect of the CsYb2F7 host and simultaneous emissions of Er and Tm activators. Importantly, the robust inorganic glass matrix endows Er/Tm:CsYb2F7 NCs with excellent water resistance and the ability to withstand high-power laser irradiation. Based on these unique characteristics, a proof-of-concept anti-counterfeiting experiment is designed. The results indicate that dynamic full-color UC luminescence patterns can be easily tuned by simply changing the power of the incident 980 nm laser. The present work not only confirms that the designed photothermal material can increase information security, but also provides a new idea for practical applications in the field of anti-counterfeiting.

Understanding the Aging Mechanism of Na-Based Layered Oxide Cathodes with Different Stacking Structures.

Manganese-based layered oxides are one of the most promising cathodes for Na-ion batteries, but the prospect of their practical application is challenged by high sensitivity to ambient air. The stacking structure of materials is critical to the aging mechanism between layered oxides and air, but there remains a lack of systematic study. Herein, comprehensive research on model materials P-type Na0.50MnO2 and O-type Na0.85MnO2 reveals that the O-phase displays a much higher dynamic affinity toward moisture air compared to P-type compounds. For air-exposed O-type material, Na+ ions are extracted from the crystal lattice to form alkaline species at the surface in contact with air, accompanying by the increase of the valence state of transition metals. The series of undesired reactions result in an increase of interfacial resistance and huge capacity loss. Comparatively, the insertion of H2O into the Na layer is the main reaction during air-exposure of P-type material, and the inserted H2O can be extracted by high-temperature treatment. The H2O de/insertion process not only causes no performance degradation but also can enlarge the interlayer distance. With these understandings, we further propose a washing-resintering strategy to recover the performance of aged O-type materials and an aging strategy to build high-performance P-type materials.

Top-down strategy synthesis of fluorinated graphdiyne for lithium ion battery.

As a novel carbon allotrope, graphdiyne exhibits excellent electrochemical properties such as high specific capacities, outstanding rate performances, and long cycle lives. These properties are attributed to its sp- and sp2-hybridized bonding and a natural large pore structure. Doping with light elements is a facile way to improve the electrochemical performance of graphdiyne. Herein, we report the preparation of fluorine-doped graphdiyne by exposure to XeF2 under a mild temperature. Compared to pristine graphdiyne, the capacities are doubled. We obtained reversible capacities of fluorinated graphdiyne up to 1080 mA h g-1 after 600 cycles at a current density of 500 mA g-1. At a higher current density of 1000 mA g-1, it still retained a high specific capacity of 693 mA h g-1 after 1000 cycles. Using in situ quantitative nanomechanical probe atomic force microscopy, we further analyzed the surface morphologies and elastic modulus to understand the mechanism of the electrochemical improvement. The fluorinated graphdiyne elastic modulus is doubled in contrast to pristine graphdiyne. The performance improvements are attributed to the improvement in conductivity and enhancement of the mechanical properties.

Suppression of Monoclinic Phase Transitions of O3-Type Cathodes Based on Electronic Delocalization for Na-Ion Batteries.

As high capacity cathodes, O3-type Na-based oxides always suffer from a series of monoclinic transitions upon sodiation/desodiation, mainly caused by Na+/vacancy ordering and Jahn-Teller (J-T) distortion, leading to rapid structural degradation and serious performance fading. Herein, a simple modulation strategy is proposed to address this issue based on refrainment of electron localization in expectation to alleviate the charge ordering and change of electronic structure, which always lead to Na+/vacancy ordering and J-T distortion, respectively. According to density functional theory calculations, Fe3+ with slightly larger radius is introduced into NaNi0.5Mn0.5O2 with the intention of enlarging transition metal layers and facilitating electronic delocalization. The obtained NaFe0.3Ni0.35Mn0.35O2 exhibits a reversible phase transition of O3hex-P3hex without any monoclinic transitions in striking contrast with the complicated phase transitions (O3hex-O'3mon-P3hex-P'3mon-P3'hex) of NaNi0.5Mn0.5O2, thus excellently improving the capacity retention with a high rate kinetic. In addition, the strategy is also effective to enhance the air stability, proved by direct observation of atomic-scale ABF-STEM for the first time.

Na+/vacancy disordering promises high-rate Na-ion batteries.

As one of the most fascinating cathode candidates for Na-ion batteries (NIBs), P2-type Na layered oxides usually exhibit various single-phase domains accompanied by different Na+/vacancy-ordered superstructures, depending on the Na concentration when explored in a limited electrochemical window. Therefore, their Na+ kinetics and cycling stability at high rates are subjected to these superstructures, incurring obvious voltage plateaus in the electrochemical profiles and insufficient battery performance as cathode materials for NIBs. We show that this problem can be effectively diminished by reasonable structure modulation to construct a completely disordered arrangement of Na-vacancy within Na layers. The combined analysis of scanning transmission electron microscopy, ex situ x-ray absorption spectroscopy, and operando x-ray diffraction experiments, coupled with density functional theory calculations, reveals that Na+/vacancy disordering between the transition metal oxide slabs ensures both fast Na mobility (10-10 to 10-9 cm2 s-1) and a low Na diffusion barrier (170 meV) in P2-type compounds. As a consequence, the designed P2-Na2/3Ni1/3Mn1/3Ti1/3O2 displays extra-long cycle life (83.9% capacity retention after 500 cycles at 1 C) and unprecedented rate capability (77.5% of the initial capacity at a high rate of 20 C). These findings open up a new route to precisely design high-rate cathode materials for rechargeable NIBs.

Single-Site AuI Catalyst for Silane Oxidation with Water.

Single-site Au anchored on mpg-C3 N4 (519 ppm Au loading) is developed as a highly active, selective, and stable catalyst for the oxidation of silanes with water with a turnover frequency as high as 50 200 h-1 , far exceeding most known catalysts based on total gold content. Other hydrosilanes bearing unsaturated functional groups also lead to corresponding silanols under mild reaction conditions without formation of any side products in good or excellent yields. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Au atoms stabilized by mpg-C3 N4 . The coordination of the catalytically active AuI by three nitrogen or carbon atoms in the tri-s-triazine repeating units not only prevents the Au atoms from aggregation, but also renders the surface AuI highly active, which is completely different than homogeneous AuI species.

Revisiting local structural changes in GeO2 glass at high pressure.

Despite the great importance in fundamental and industrial fields, understanding structural changes for pressure-induced polyamorphism in network-forming glasses remains a formidable challenge. Here, we revisited the local structural transformations in GeO2 glass up to 54 GPa using x-ray absorption fine structure (XAFS) spectroscopy via a combination diamond anvil cell and polycapillary half-lens. Three polyamorphic transitions can be clearly identified by XAFS structure refinement. First, a progressive increase of the nearest Ge-O distance and bond disorder to a maximum at ~5-16 GPa, in the same pressure region of previously observed tetrahedral-octahedral transformation. Second, a marked decrease of the nearest Ge-O distance at ~16-22.6 GPa but a slight increase at ~22.6-32.7 GPa, with a concomitant decrease of bond disorder. This stage can be related to a second-order-like transition from less dense to dense octahedral glass. Third, another decrease in the nearest Ge-O distance at ~32.7-41.4 GPa but a slight increase up to 54 GPa, synchronized with a gradual increase of bond disorder. This stage provides strong evidence for ultrahigh-pressure polyamorphism with coordination number >6. Furthermore, cooperative modification is observed in more distant shells. Those results provide a unified local structural picture for elucidating the polyamorphic transitions and densification process in GeO2 glass.

Novel P2-type Na2/3Ni1/6Mg1/6Ti2/3O2 as an anode material for sodium-ion batteries.

A novel P2-type Na2/3Ni1/6Mg1/6Ti2/3O2 material is explored as an anode for sodium-ion batteries (SIBs) for the first time. It delivers a reversible capacity of 92 mA h g-1 with a safe average storage voltage of approximately 0.7 V in a sodium half-cell, and exhibits good cycle stability (ca. 87.4% capacity retention for 100 cycles) at a cut-off voltage of 0.2-2.5 V, indicating its superiority as a promising candidate anode material for SIBs.

Ti-Substituted NaNi0.5 Mn0.5-x Tix O2 Cathodes with Reversible O3-P3 Phase Transition for High-Performance Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have been considered as potential candidates for stationary energy storage because of the low cost and wide availability of Na sources. O3-type layered oxides have been considered as one of the most promising cathodes for SIBs. However, they commonly show inevitable complicated phase transitions and sluggish kinetics, incurring rapid capacity decline and poor rate capability. Here, a series of sodium-sufficient O3-type NaNi0.5 Mn0.5-x Ti x O2 (0 ≤ x ≤ 0.5) cathodes for SIBs is reported and the mechanisms behind their excellent electrochemical performance are studied in comparison to those of their respective end-members. The combined analysis of in situ X-ray diffraction, ex situ X-ray absorption spectroscopy, and scanning transmission electron microscopy for NaNi0.5 Mn0.2 Ti0.3 O2 reveals that the O3-type phase transforms reversibly into a P3-type phase upon Na+ deintercalation/intercalation. The substitution of Ti for Mn enlarges interslab distance and could restrain the unfavorable and irreversible multiphase transformation in the high voltage regions that is usually observed in O3-type NaNi0.5 Mn0.5 O2 , resulting in improved Na cell performance. This integration of macroscale and atomicscale engineering strategy might open up the modulation of the chemical and physical properties in layered oxides and grasp new insight into the optimal design of high-performance cathode materials for SIBs.

Subzero-Temperature Cathode for a Sodium-Ion Battery.

A subzero-temperature cathode material is obtained by nucleating cubic prussian blue crystals at inhomogeneities in carbon nanotubes. Due to fast ionic/electronic transport kinetics even at -25 °C, the cathode shows an outstanding low-temperature performance in terms of specific energy, high-rate capability, and cycle life, providing a practical sodium-ion battery powering an electric vehicle in frigid regions.