The Compatibility of COFs Cathode and Optimized Electrolyte for Ultra-Long Lifetime Rechargeable Aqueous Zinc-Ion Battery.

Rechargeable aqueous zinc-ion batteries (RAZIBs) are attractive due to their affordability, safety, and eco-friendliness. However, their potential is limited by the lack of high-capacity cathodes and compatible electrolytes needed for reliable performance. Herein, we have presented a compatibility strategy for the development of a durable and long-lasting RAZIBs. The covalent organic frameworks (COFs) based on anthraquinone (DAAQ-COF) is created and utilized as the cathode, with zinc metal serving as the anode. The electrolyte is made up of an aqueous solution containing zinc salts at various concentrations. The COF cathode has been designed to be endowed with a rich array of redox-active groups, enhancing its electrochemical properties. Meanwhile, the electrolyte is formulated using triflate anions, which have exhibited superiority over sulfate anions. This strategy lead to the development of an optimized COF cathode with fast charging capability, high Coulombic efficiency (nearly 100 %) and long-term cyclability (retention rate of nearly 100 % at 1 A g-1 after 10000 cycles). Moreover, through experimental analysis, a co-insertion mechanism involving Zn2+ and H+ in this cathode is discovered for the first time. These findings represent a promising path for the advancement of organic cathode materials in high-performance and sustainable RAZIBs.

Water-Stable Microporous Bipyrazole-Based Framework for Efficient Separation of MTO Products.

Recently, methanol-to-olefins (MTO) technology has been widely used. The development of new adsorbents to separate MTO products and obtain high-purity ethylene (C2H4) and propylene (C3H6) has become an urgent task. Herein, an exceptionally highly water-stable metal-organic framework (MOF), [Cu3(OH)2(Me2BPZ)2]·(solvent)x (1) (H2Me2BPZ = 3,3'-dimethyl-1H,1'H-4,4'-bipyrazole) with hexagonal pores, has been elaborately designed and constructed. After being soaked in water for 7 days, it still maintains its structure, and the uptake of N2 at 77 K is unchanged. The adsorption capacity of C3H6 can reach 138 cm3 g-1, while the uptake of C2H4 is only 52 cm3 g-1 at 298 K and 1 bar. The dynamic breakthrough experiments show that the mixture of C3H6/C2H4 (50/50, v/v) can be efficiently separated in one step. High-purity C2H4 and C3H6 can be obtained through an adsorption and desorption cycle and the yields of C2H4 (purity ≥ 99.95%) and C3H6 (purity ≥ 99%) are 84 and 48 L kg-1, respectively. Surprisingly, when the flow rate is increased, the separation performance has no obvious change. Additionally, humidity has no effect on the separation performance. Finally, theoretical simulations indicate that there are stronger interactions between the C3H6 molecule and the framework, which are beneficial to capturing C3H6 over C2H4.

Dual Strategies of Metal Preintercalation and In Situ Electrochemical Oxidization Operating on MXene for Enhancement of Ion/Electron Transfer and Zinc-Ion Storage Capacity in Aqueous Zinc-Ion Batteries.

As an emerging two-dimensional material, MXenes exhibit enormous potentials in the fields of energy storage and conversion, due to their superior conductivity, effective surface chemistry, accordion-like layered structure, and numerous ordered nanochannels. However, interlayer accumulation and chemical sluggishness of structural elements have hampered the demonstration of the superiorities of MXenes. By metal preintercalation and in situ electrochemical oxidization strategies on V2 CTx , MXene has enlarged its interplanar spacing and excited the outermost vanadium atoms to achieve frequent transfer and high storage capacity of Zn ions in aqueous zinc-ion batteries (ZIBs). Benefiting from the synergistic effects of these strategies, the resulting VOx /Mn-V2 C electrode exhibits the high capacity of 530 mA h g-1 at 0.1 A g-1 , together with a remarkable energy density of 415 W h kg-1 and a power density of 5500 W kg-1 . Impressively, the electrode delivers excellent cycling stability with Coulombic efficiency of nearly 100% in 2000 cycles at 5 A g-1 . The satisfactory electrochemical performances bear comparison with those in reported vanadium-based and MXene-based aqueous ZIBs. This work provides a new methodology for safe preparation of outstanding vanadium-based electrodes and extends the applications of MXenes in the energy storage field.

Highly Stable Metal-Organic Framework with Redox-Active Naphthalene Diimide Core as Cathode Material for Aqueous Zinc-Ion Batteries.

Recently, metal-organic frameworks (MOFs) as the cathode materials for aqueous zinc-ion batteries (ZIBs) received growing attention. Herein, a novel MOF, Ni-Ndi-trz (Ndi-trz=2,7-di(4H-1,2,4-triazol-4-yl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone) was synthesized through a solvothermal method. Its rational design using a naphthalene diimide (Ndi) core allowed the formation of a four-fold interpenetrated pcu (primitive cubic) topology. The as-synthesized Ni-Ndi-trz is highly stable over a wide pH range (0-12) for 30 days, which is critical to ensure the decent cyclability of zinc-ion batteries (ZIBs). When used as the cathode material of ZIBs, it shows a high initial specific capacity of 90.7 mAh g-1 and excellent cycling stability. Remarkably, three-electrode system tests, ex situ FTIR, UV/Vis and XPS spectra revealed that the Ndi core of Ni-Ndi-trz undergoes a reversible interconversion between the keto and enol forms when interacting with Zn2+ ions. This work may shed light on the feasibility of designing novel MOFs and exploring their mechanisms for zinc ion batteries.

Assessing Susceptibility of Debris Flow in Southwest China Using Gradient Boosting Machine.

A gradient boosting machine (GBM) was developed to model the susceptibility of debris flow in Sichuan, Southwest China for risk management. A total of 3839 events of debris flow during 1949-2017 were compiled from the Sichuan Geo-Environment Monitoring program, field surveys, and satellite imagery interpretation. In the cross-validation, the GBM showed better performance, with the prediction accuracy of 82.0% and area under curve of 0.88, than the benchmark models, including the Logistic Regression, the K-Nearest Neighbor, the Support Vector Machine, and the Artificial Neural Network. The elevation range, precipitation, and aridity index played the most important role in determining the susceptibility. In addition, the water erosion intensity, road construction, channel gradient, and human settlement sites also largely contributed to the formation of debris flow. The susceptibility map produced by the GBM shows that the spatial distributions of high-susceptibility watersheds were highly coupled with the locations of the topographical extreme belt, fault zone, seismic belt, and dry valleys. This study provides critical information for risk mitigating and prevention of debris flow.