Harnessing Polymer-Matrix-Mediated Manipulation of Intermolecular Charge-Transfer for Near-Infrared Security Applications.

Precise recognition of near-infrared (NIR) signals holds great prospects in optical communication, remote sensing, information security, and anti-counterfeiting. For these applications, filters with good NIR transparency are typically essential components. Currently, such NIR transparent filters are dominated by inorganic materials such as chalcogenide glasses. There are, so far, only a handful of organic molecules with suitable optical properties due to the rarity of organic materials with good NIR transparency and relatively flat absorption over the UV-visible region. Here, it is found that the library of NIR-transparent organic materials can be expanded by forming a charge-transfer complex (CTC) between a donor (D) and an acceptor (A) molecule that are commercially available. Via regulating the DA interaction, the CTC filter shows tunable absorption from the visible to NIR region with a relatively high penetration of NIR radiation (≈80%). The CTC filter can successfully highlight NIR information hidden in a complex environment and allow reading of NIR security images for advanced anti-counterfeiting. Moreover, the CTC filter can be used for viewing protected NIR information with good resolution, and thus provide a convenient tool for different security applications using NIR-encoded information.

Anchoring Copper Single Atoms on Porous Boron Nitride Nanofiber to Boost Selective Reduction of Nitroaromatics.

Single-atom catalysts have received widespread attention for their fascinating performance in terms of metal atom efficiency as well as their special catalysis mechanisms compared to conventional catalysts. Here, we prepared a high-performance catalyst of single-Cu-atom-decorated boron nitride nanofibers (BNNF-Cu) via a facile calcination method. The as-prepared catalyst shows high catalytic activity and good stability for converting different nitro compounds into their corresponding amines both with and without photoexcitation. By combined studies of synchrotron radiation analysis, high-resolution high-angle annular dark-field transmission electron microscopy studies, and DFT calculations, dispersion and coordination of Cu atoms as well as their catalytic mechanisms are explored. The BNNF-Cu catalyst is found to have a record high turnover frequency compared to previously reported non-precious-metal-based catalysts. While the performance of the BNNF-Cu catalyst is only of the middle range level among the state-of-the-art precious-metal-based catalysts, due to the much lower cost of the BNNF-Cu catalyst, its cost efficiency is the highest among these catalysts. This work provides a choice of support material that can promote the development of single-atom catalysts.

3D Ag@C Cloth for Stable Anode Free Sodium Metal Batteries.

While sodium metal anodes (SMAs) feature many performance advantages in sodium ion batteries (SIBs), severe safety concerns remain for using bulk sodium electrodes. Herein, a 3D Ag@C natrophilic substrate prepared by a facile thermal evaporation deposition method, which can be employed as a much safer "anode-free" SMA, is reported. Initially, there is no bulk sodium on the Ag@C substrate in the assembled SIBs. Upon charging, sodium will be uniformly deposited onto the Ag@C substrate and afterwards functions as a real SMA, thus inheriting the intrinsic merits of SMA and enhancing safety simultaneously. While cycling, the as-synthesized substrate demonstrates superior sodium plating/stripping cycling stability at 1, 2 and 3 mA cm-2 with a capacity of 2 mAh cm-2 . Theoretical simulations reveal that Na ions prefer to bind with Ag and form a Na-Ag network, thus clearly revealing uniform sodium deposition on the Ag@C substrate. More importantly, a full battery based on Ag@C and Prussian white with impressive Coulomb efficiency (CE), high rate capability (from 0.1 C to 5 C) and long-term cycling life is illustrated for the first time, thus making Ag@C feasible for the establishment of "anode-free" SIBs with reduced cost, high gravimetric/volumetric energy density and enhanced safety.

Aqueous MnV2 O6 -Zn Battery with High Operating Voltage and Energy Density.

Aqueous Zn ion batteries (AZIBs), featuring low cost, long-term cycling stability, and superior safety are promising for applications in advanced energy storage devices. However, they still suffer from unsatisfactory energy density and operating voltage, which are closely related to cathode materials used. Herein, the use of monoclinic MnV2 O6 (MVO) is reported, which can be activated for high-capacity Zn ions storage by electrochemically oxidizing part of the Mn2+ to Mn3+ or Mn4+ while the remaining Mn2+ ions act as binders/pillars to hold the layer structure of MVO and maintain its integrity during charging/discharging process. Moreover, after introducing carbon nanotubes (CNT), the MVO:CNT composite not only provides robust 3D Zn-ion diffusion channels but also shows enhanced structural integrity. As a result, a MVO:CNT cathode delivers a high midpoint voltage (1.38 V after 3000 cycles at 2 A g-1 ) and a high energy density of 597.9 W h kg-1 . Moreover, DFT analyses clearly illustrate stepwise Zn ion insertion into the MnV2 O6 lattice, and ex-situ analyses results further verify the highly structural reversibility of the MnV2 O6 cathode upon extended cycling, demonstrating the good potential of MnV2 O6 for the establishment of viable aqueous Zn ion battery systems.

Mechanisms of sodiation in anatase TiO2 in terms of equilibrium thermodynamics and kinetics.

Anatase TiO2 is a promising anode material for sodium-ion batteries (SIBs). However, its sodium storage mechanisms in terms of crystal structure transformation during sodiation/de-sodiation processes are far from clear. Here, by analyzing the redox thermodynamics and kinetics under near-equilibrium states, we observe, for the first time, that upon Na-ion uptake, the anatase TiO2 undergoes a phase transition and then an irreversible crystal structure disintegration. Additionally, unlike previous theoretical studies which investigate only the two end points of the sodiation process (i.e., TiO2 and NaTiO2), we study the progressive crystal structure changes of anatase TiO2 upon step-by-step Na-ion uptake (Na x TiO2, x = 0.0625, 0.125, 0.25, 0.5, 0.75, and 1) for the first time. It is found that the anatase TiO2 goes through a thermodynamically unstable intermediate phase (Na0.25TiO2) before reaching crystalline NaTiO2, confirming the inevitable crystal structure disintegration during sodiation. These combined experimental and theoretical studies provide new insights into the sodium storage mechanisms of TiO2 and are expected to provide useful information for further improving the performance of TiO2-based anodes for SIB applications.

Porous BN Nanofibers Enable Long-Cycling Life Sodium Metal Batteries.

Sodium metal anode, featuring high capacity, low voltage and earth abundance, is desirable for building advanced sodium-metal batteries. However, Na-ion deposition typically leads to morphological instability and notorious chemical reactivity between sodium and common electrolytes still limit its practical application. In this study, a porous BN nanofibers modified sodium metal (BN/Na) electrode is introduced for enhancing Na-ion deposition dynamics and stability. As a result, symmetrical BN/Na cells enable an impressive rate capability and markedly enhanced cycling durability over 600 h at 10 mA cm-2 . Density functional theory simulations demonstrate BN could effectively improve Na-ion adsorption and diffusion kinetics simultaneously. Finite element simulation clearly reveals the intrinsic smoothing effect of BN upon multiple Na-ion plating/stripping cycles. Coupled with a Na3 V2 O2 (PO4 )2 F/Ti3 C2 X cathode, sodium metal full cells offer an ultrastable capacity of 125/63 mA h g-1 (≈420/240 Wh kg-1 ) at 0.05/5 C rate over 500 cycles. These comprehensive analyses demonstrate the feasibility of BN/Na anode for the establishment of high-energy-density sodium-metal full batteries.

Three-Dimensional Rigidity-Reinforced SiOx Anodes with Stabilized Performance Using an Aqueous Multicomponent Binder Technology.

Three-dimensional (3D) rigidity-reinforced SiOx anodes are prepared using the aqueous multicomponent binders to stabilize the performances of lithium-ion batteries. Considering an elastic skeleton, adhesiveness, electrolyte absorption, etc., four kinds of binders [polyacrylamide (PAM), poly(tetrafluoroethylene) (PTFE), carboxymethyl cellulose, and styrene butadiene rubber (SBR)] are selected to prepare aqueous multicomponent binders. The SiOx anodes with the binder PAM/SBR/PTFE (PSP) exhibit a 3D rigidity-reinforced structure, larger adhesive force, and moderate electrolyte adsorption capacity compared to other anodes with single and multicomponent binders. Specifically, the electrochemical performances of the SiOx anodes with the binder PSP663 are stabilized, and a retention capacity of 770 mAh g-1 at 500 mA g-1 after 300 cycles and a rate capacity of 993 mAh g-1 at 1200 mA g-1 are obtained. The enhanced performances are attributed to the good chemical stability of PTFE to protect SiOx particles from the electrolyte corrosion and to ensure electrode integrity. SBR acts as the binder backbone due to the strong adhesion force and specific three-dimensional structure. The rigidity of PAM limits the excessive expansion of SiOx particles well and shortens the ion migration. These results indicate that the 3D rigidity-reinforced SiOx anode with the aqueous binder PSP663 has promising prospects for practical application, and the results also provide a reference for solving the expansion problem of the silicon materials.