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3833 mAh cm −3 nearly double that of lithium (2062 mAh cm −3 ), and exhibits a relatively negative reduction potential of −2.4 V versus standard hydrogen electrode (SHE). [6][7][8][9] Despite of these intriguing merits, the practical employment of RMBs is hampered by several main hurdles. First, clumsy Mg 2+ intercalation is the primary limitation for the choice of competent cathode materials, because the strong Coulombic interactions between the divalent Mg 2+ ions and the anions in the host materials often result in sluggish diffusion kinetics and slow interfacial charge transfer. [10][11][12][13] Second, to design appropriate electrolytes for Mg plating/ stripping with high Coulombic efficiency, wide electrochemical window, and good compatibility with the cathodic materials is another great challenge. [14,15] Therefore, to develop advanced cathode materials capable of rapid Mg 2+ insertion/extraction in suitable electrolytes for reversible Mg plating/stripping is highly desirable. Since the pioneering work of Chevrel phase compounds (Mo 6 S 8 ) reported by Aurbach et al. in 2000, [16] tremendous efforts have been devoted to develop cathode materials for RMBs, including transition metal oxides (MnO 2 , V 2 O 5 , Mn 3 O 4 , WO 3 , Co 3 O 4 ), [17-21] polyanionic compounds (Mg 1.03 Mn 0.97 SiO 4 , MgCoSiO 4 ), [22,23] and transition metal dichalcogenides (TMDs, such as TiS 2 , MoS 2 , WSe 2 ). [24][25][26][27][28] However, most oxides and polyanionic compounds suffer from low capacity and poor cycling performance owing to the strong interactions between divalent Mg 2+ and O 2− in the hosts. [25,29] On the contrary, TMDs are deemed to be a class of promising cathode materials with more favorable kinetics, attributing to the relatively weaker MgS or MgSe bonds than MgO bond. [25,28,30] Nevertheless, layered TMDs also suffer from slow Mg 2+ ion diffusion due to the narrow interlayer spacing and the high polarity of Mg 2+ . [31] Recently, it was reported that the interlayer distances of TMDs could be expanded by intercalating guest molecules (water or organic molecules), enlarging the dimension of ion diffusion channels and shielding the Coulombic interactions between Mg 2+ and the lattice anions of hosts. 13,27 In addition, the intercalated molecules served as interlayer pillars are conducive to maintain the framework of host materials for prolonged cycles. [32,33] Rechargeable magnesium batteries (RMBs) are attractive candidates for large-scale energy storage owing to the high theoretical specific capacity, rich earth abundance, and good safety characteristics. However, the development of desirable cathode materials for RMBs is constrained by the high polarity and slow intercalation kinetics of Mg 2+ ions. Herein, it is demonstrated that 2-ethylhexylamine pillared vanadium disulfide nanoflowers (expanded VS 2 ) with enlarged interlayer distances exhibit greatly boosted electrochemical performance as a cathode material in RMBs. Through a one-step solution-phase synthesis and in situ 2-ethylhexylamine intercalatio...

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Considerable efforts have been devoted on the design and fabrication of non-platinum electrocatalysts with high performance and low cost for hydrogen evolution reaction (HER). However, the catalytic activity of existing electrocatalysts usually subjects to the limited amount of exposed active sites. Herein ,we propose that self-assembled ultrathin NiCo 2 S 4 nanoflakes grown on nickel foam (NiCo 2 S 4 /Ni foam) can serve as excellent electrocatalyst for HER in alkaline solution with high activity and stability. The NiCo 2 S 4 /Ni foam electrodes were prepared by the complete sulfidation of networked ultrathin NiCo-layered double hydroxide nanoflakes grown on Ni foam (NiCo-LDH/Ni foam). The advantages of this unique architecture are that the ultrathin and porous NiCo 2 S 4 nanoflakes can provide a huge number of exposed active sites, the highly-conductive Ni foam can promote the transfer of electrons, and the three-dimensional-networked structure can facilitate the diffusion and penetration of electrolyte. Electrochemical measurements reveal that NiCo 2 S 4 /Ni foam electrodes exhibit greatly improved performance than NiCo-LDH/Ni foam for HER in alkaline solution with low onset overpotential (17 mV), small Tafel slope (84.5 mV/dec) and excellent long-duration cycling stability (maintaining an onset overpotential of ~20 mV and an overpotential of 155 mV at 50 mA/cm 2 after testing for 100,000 seconds). In addition, the highly-flexible NiCo 2 S 4 /Ni foam electrodes show no obvious catalytic degradation after bending for 200 times, confirming the high flexibility and robustness under severe conditions.

Herein, we report a unique thermal synthesis method to prepare a novel two-dimensional (2D) hybrid nanostructure consisting of ultrathin and tiny-sized molybdenum disulfide nanoplatelets homogeneously inlaid in graphene sheets (MoS2/G) with excellent electrocatalytic performance for HER. In this process, molybdenum oleate served as the source of both molybdenum and carbon, while crystalline sodium sulfate (Na2SO4) served as both reaction template and sulfur source. The remarkable integration of MoS2 and graphene in a well-assembled 2D hybrid architecture provided large electrochemically active surface area and a huge number of active sites and also exhibited extraordinary collective properties for electron transport and H+ trapping. The MoS2/G inlaid nanosheets deliver ultrahigh catalytic activity toward HER among the existing electrocatalysts with similar compositions, presenting a low onset overpotential approaching 30 mV, a current density of 10 mA/cm2 at ∼110 mV, and a Tafel slope as small as 67.4 mV/dec. Moreover, the strong bonding between MoS2 nanoplatelets and graphene enabled outstanding long-term electrochemical stability and structural integrity, exhibiting almost 100% activity retention after 1000 cycles and ∼97% after 100 000 s of continuous testing (under static overpotential of −0.15 V). The synthetic strategy is simple, inexpensive, and scalable for large-scale production and also can be extended to diverse inlaid 2D nanoarchitectures with great potential for many other applications.

Bi2MoO6/OV-BiOBr heterojunctions are synthesized and show good photocatalytic activities for nitrogen reduction to ammonia under ambient conditions.

The design of electrochemically active materials with appropriate structures and compositions is very important for applications in energy conversion and storage devices. Herein, we demonstrate an effective strategy to prepare microporous heteroatom-doped carbon frameworks derived from naturally-abundant pine needles. The preparation procedure is based on the carbonization of pine needles, followed by KOH activation at a temperature range of 700-1000 °C. The resultant nitrogen-doped carbon consists of abundant micropores and an ultrahigh specific surface area (up to 2433 m g), leading to high performances in electrocatalytic hydrogen evolution reaction (HER) and supercapacitors. Specifically, when the pine needle-derived carbon (activated at 800 °C) serves as a HER electrocatalyst, it exhibits a low onset potential (∼4 mV), a small Tafel slope (∼45.9 mV dec) and a remarkable stability over long-term cycling. When evaluated as an electrode material for supercapacitors, the pine needle-derived carbon (activated at 900 °C) demonstrates high specific capacitance (236 F g at 0.1 A g), remarkable rate capability (183 F g at even 20 A g) and good long-term stability. Notably, the specific capacitance at 2.0 A g increased from ∼205 to ∼227 F g after cycling for 5000 times, owing to the further activation and wetting of the electrodes. This novel and low-cost biomass-derived carbon material is very promising for many applications, especially in electrocatalytic water splitting and supercapacitors.

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