Lithium-sulfur (Li-S) batteries hold great promise for the applications of high energy density storage. However, the performances of Li-S batteries are restricted by the low electrical conductivity of sulfur and shuttle effect of intermediate polysulfides. Moreover, the areal loading weights of sulfur in previous studies are usually low (around 1-3 mg cm) and thus cannot fulfill the requirement for practical deployment. Herein, we report that porous-shell vanadium nitride nanobubbles (VN-NBs) can serve as an efficient sulfur host in Li-S batteries, exhibiting remarkable electrochemical performances even with ultrahigh areal sulfur loading weights (5.4-6.8 mg cm). The large inner space of VN-NBs can afford a high sulfur content and accommodate the volume expansion, and the high electrical conductivity of VN-NBs ensures the effective utilization and fast redox kinetics of polysulfides. Moreover, VN-NBs present strong chemical affinity/adsorption with polysulfides and thus can efficiently suppress the shuttle effect via both capillary confinement and chemical binding, and promote the fast conversion of polysulfides. Benefiting from the above merits, the Li-S batteries based on sulfur-filled VN-NBs cathodes with 5.4 mg cm sulfur exhibit impressively high areal/specific capacity (5.81 mAh cm), superior rate capability (632 mAh g at 5.0 C), and long cycling stability.

Doping ordered mesoporous carbon with electron-donating nitrogen and sulfur heteroatoms is a promising strategy to enhance its electrochemical performance. Here we demonstrate the successful fabrication of nitrogen and sulfur co-doped ordered mesoporous carbon (NSOMC) materials with high specific surface areas (978-1021 m 2 g À1 ), large pore volumes (1.10-1.20 cm 3 g À1 ), highly-ordered pore structures and controlled dopant contents (10.0-4.8 at.% for nitrogen and 1.7-2.6 at.% for sulfur) using the oligomer of pyrrole as the precursor and sulphuric acid as the catalyst and sulfur source. NSOMC materials exhibit enhanced electrochemical double-layer capacitance (EDLC) performances due to their improved surface activity and conductivity compared with pure carbon CMK-3. The fabrication of nitrogen and sulfur co-doped ordered mesoporous carbon with enhanced electrochemical capacitance performance provides a viable route to promote its applications in electronic devices.

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In this contribution, nitrogen- and sulfur-codoped 3D cubic-ordered mesoporous carbon (KNOMC) materials with controlled dopant content (10.0-4.6 atom % for nitrogen and 0.94-0.75 atom % for sulfur) are presented, using KIT-6 as the template and pyrrole as the precursor, and its supercapacitive behavior is also investigated. The presented materials exhibit excellent supercapacitive performance by combining electrical double-layer capacitance and pseudocapacitance as well as the enhanced wettability and improved conductivity generated from the incorporation of nitrogen and sulfur into the framework of carbon materials. The specific capacitance of the presented materials reaches 320 F g(-1) at a current density of 1 A g(-1), which is significantly larger than that of the pristine-ordered mesoporous carbon reported in the literature and can even compete with some metal oxides and conducting polymers.

Cobalt (Co) and lithium (Li), rare and valuable elements, are mainly used to prepare lithium cobalt oxide (LiCoO2) for applications in lithium-ion batteries (LIBs). Developing an effective method to recover Co and Li from the waste LIBs is of great significance. In the present study, Co and Li were extracted from pure LiCoO2 powders and the extracted cathode materials powders from the waste LIBs after acid dissolution via a mechanochemical reduction process with iron powders. For pure LiCoO2 powders, the effects of Fe to LiCoO2 mass ratio, rotation speed, and mechanochemical reduction time were examined. These parameters influenced positively the extraction of Co, while they showed negligible effects on the leaching of Li. The X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicated a promoted extraction of Li arising from the reduction of particle sizes, magnification of specific surface area, and change of the crystal structure of particles. For high-efficiency leaching of Co by the mechanochemical reduction process with iron powders, X-ray photoelectron spectroscopy (XPS) analysis indicated the changes in the valence state of Co. The actual cathode materials disassembled from the wasted LIBs pretreated by this novel mechanochemical reduction process were also explored. The results indicated that the leaching ratios of Li, Co, Mn, and Ni could reach 77.15%, 91.25%, 100%, and 99.9%, respectively. This novel mechanochemical process would be of great importance for the recovery of valuable metals from waste LIBs.

Single-atom catalysis has recently emerged as a promising approach for catalyzing the carbon dioxide reduction reaction (CO2RR). In this study, we present a principle for designing active single-atom catalysts (SACs) for CO2RR. We systematically examine totally 24 transition metals supported by a graphitic carbon nitride (g-CN) monolayer and find that their catalytic activities are highly correlated with the adsorption free energies of two intermediate species (OH and OCH). We then identify two important intrinsic descriptors, namely, the number of electrons in the outmost d-shell and the enthalpy of vaporization of the transition metal. Test calculations on transition metals supported by a C2N monolayer indicate that both descriptors are quite universal for SACs of CO2RR. Based on these results, we show that Ni@g-CN, Cu@g-CN, and Co@C2N are promising SACs for CO2RR. This study offers an effective principle for designing highly active SACs for CO2RR on the basis of intrinsic properties of transition metals.

From both energy and environmental points of view, it is highly desirable to produce organic compounds from greenhouse gas CO2. To reach such an attractive goal, high-performance catalysts are required. In this study, a new family of two-dimensional (2D) materials, transition-metal diboride (MB2), are theoretically designed. With intrinsic transition-metal-terminated surfaces, MB2 monolayers exhibit a high catalytic activity for the conversion of CO2 selectively to CH4. In particular, the OsB2 monolayer has an ultralow limiting potential of −0.4 V for CH4 production. Non-noble-metal-based FeB2 and MnB2 also have a low limiting potential, and they are thus very promising for practical applications. Atomistic mechanisms of the catalyzed CO2 conversion are understood based on the first-principles calculations. Oxygen binding energy is found to be a good descriptor for the catalytic performance, and the activity “volcano” plot suggests that, in the OsB2 case, it is very close to the optimal value of 6.4 eV. The outstanding catalytic performance of this new type of 2D materials makes them especially attractive for CO2 utilization.

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