Direct regeneration of waste LiFePO4 cathode materials with a solid-phase method promoted by activated CNTs.

Annually increasing electric vehicles will undoubtedly end in tremendous amount of waste LiFePO4 (LFP) batteries. In this work, a highly-efficient and easy-going solid-phase method is proposed for direct regeneration of the waste LFP cathode material (W-LFP). The W-LFP is successfully regenerated via heat treatment with the addition of Li2CO3, CNTs and glucose. After activation, the dispersibility of CNTs in water is improved, making it easier to mix well with other materials. Also, the hydroxyl and carboxyl groups on CNTs have a certain degree of reducibility, which is conducive to the reduction of Fe3+ to Fe2+. After subsequent heat treatment, the three-dimensional conductive network composed of CNTs greatly enhances the conductivity and the ionic diffusion coefficient of LFP, thereby improving its electrochemical performance. Meanwhile, the decay and regeneration mechanisms of LFP are investigated by characterization and electrochemical testing. The regenerated LFP achieves an excellent specific capacity of 155.47 mAh/g at 0.05 C, which is around 99% that of new LFP. Additionally, the costs of main consumption in the regeneration process only account for 33.7% the price of new LFP. This low-cost, high-value-added and solid-phase direct regeneration process is proved to have great economic and energy-saving potential, which is promising for recycling the waste LFP cathode materials.

Metal-Organic Frameworks for Electrocatalytic Sensing of Hydrogen Peroxide.

The electrochemical detection of hydrogen peroxide (H2O2) has become more and more important in industrial production, daily life, biological process, green energy chemistry, and other fields (especially for the detection of low concentration of H2O2). Metal organic frameworks (MOFs) are promising candidates to replace the established H2O2 sensors based on precious metals or enzymes. This review summarizes recent advances in MOF-based H2O2 electrochemical sensors, including conductive MOFs, MOFs with chemical modifications, MOFs-composites, and MOF derivatives. Finally, the challenges and prospects for the optimization and design of H2O2 electrochemical sensors with ultra-low detection limit and long-life are presented.

Hexagonal Single-Crystal CoS Nanosheets: Controllable Synthesis and Tunable Oxygen Evolution Performance.

Cobalt-based sulfides with variable valence states and unique physical and chemical properties have shown great potential as oxygen evolution reaction (OER) catalysts for electrochemical water-splitting reactions. However, poor morphological characteristics and a small specific surface area limit its further application. Here, hexagonal single-crystal two-dimensional (2D) CoS nanosheets with different thicknesses are successfully prepared by an atmospheric-pressure chemical vapor deposition method. Because of the advantages of the 2D structure, more exposed catalytic active sites, better reactant adsorption ability, accelerated electron transfer, and enhanced electrical conductivities can be achieved from the thinnest 5 nm CoS nanosheets (CoS-5), significantly improving OER performance. The electrochemical tests manifest that CoS-5 show an overpotential of 290 mV at 10 mA cm-2 and a Tafel slope of 65.6 mV dec-1 in the OER in an alkaline solution, superior to those for other thicknesses of CoS, bulk CoS, and RuO2. For the mechanistic investigation, the lowest charge transfer resistance (Rct) and the highest double-layer capacitance (Cdl) were obtained for CoS-5, demonstrating the faster OER kinetics and the larger active area. Density functional theory calculations further reveal the enhanced density of states around the Fermi level and higher H2O molecule adsorption energy for thinner CoS nanosheets, promoting its intrinsic catalytic activity. Moreover, the two-electrode system with CoS-5 as the anode and Pt/C as the cathode requires only 1.56 V to attain 10 mA cm-2 in the overall water-splitting reaction. We believe that this study will provide a fresh view for thickness-dependent catalytic performance and offers a new material for the study of electronic and energy devices.

Synthesis of transition metal dichalcogenide van der Waals heterostructures through chemical vapor deposition.

Transition metal dichalcogenide (TMD) van der Waals (vdW) heterostructures show great potential in the exploration of novel physical phenomena and practical applications. Compared to the traditional mechanical stacking techniques, chemical vapor deposition (CVD) method exhibits more advantages in preparing TMD vdW heterostructures. CVD enables the large-scale production of high-quality materials with clean interfaces in the future. Herein, CVD methods for the synthesis of TMD vdW heterostructures are summarized. These methods are categorized in two major strategies, multi-step process and one-step process. The effects of various factors are demonstrated, including the temperature, nucleation, and precursors. Finally, the remaining challenges are discussed.

MOF-derived CoNi,CoO,NiO@N-C bifunctional oxygen electrocatalysts for liquid and all-solid-state Zn-air batteries.

Metal-organic framework (MOF)-derived carbon composites with embedded metal alloy/metal oxides have attracted much attention due to their low-cost and excellent electrochemical reactivity. However, the drawback of this concept is the severe carbon evaporation during their synthesis, resulting in a reduction of active sites and catalytic durability. To solve this problem, this study proposes the possibility of using Ketjen black (KB) to replenish the carbon content. Impressively, MOF-derived bimetal and oxide N-doped porous carbon (CoNi-CoO-NiO@NC-800) exhibits extremely high catalytic activity with an oxygen reduction reaction (half-wave potential: 0.83 V) and oxygen evolution reaction (overpotential: 352 mV @ 10 mA cm-2) potential gap of 0.75 V due to the virtue of the hierarchically porous structure and sufficient active sites. By combining theoretical studies, a strong synergetic coupling of the CoNi dual metal is proposed in decreasing the overall reaction barriers and promoting the reversible oxygen reactions. Moreover, the assembled liquid- and all-solid-state Zn-air batteries (ZABs) with the bifunctional catalyst as the air cathode demonstrate superior discharging (223 mW cm-2 at 310 mA cm-2) and charging-discharging performance and long lifetime (450 cycles, 75 h). This work will provide guidance for the rational design of metal/carbon hybrid catalysts and cut-price reproducible energy systems.

Solvent-assisted thermal reduction of microcrystalline graphene oxide with excellent microwave absorption performance.

To prepare a new kind of electromagnetic wave absorber, and improve the processing technology and accessional value of natural microcrystalline graphite minerals (NMGMs), reduced microcrystalline graphene oxide (rGO-M), a novel absorber with high absorption, low reflection and a wide absorption band, was prepared from NMGMs using a solvent-assisted thermal reduction method. Moreover, the as-produced rGO-M with adjustable electrical resistivity can be easily transferred into well distributed bulk materials by freeze-drying technology. These unique structures and compositions make a great contribution to the impedance match, and cause strong conductive loss and various dipole polarization effects which greatly enhance the absorption. Meanwhile, the effective bandwidths below -5 dB and -10 dB are 11.7 GHz and 3.32 GHz respectively, and the reflection loss can reach -42.68 dB. The study will be beneficial to the development of carbon resources and carbon materials research. Besides, it can provide a scientific basis for the further improvement of the comprehensive utilization and the level of deep processing technology of NMGM resources.