Atomically dispersed transition metals confined with nitrogen on a carbon support has demonstrated great electrocatalytic performance, but an extremely low concentration of metal atoms (usually below 1.5%) is necessary to avoid aggregation through sintering which limits mass activity. Here, a salt‐template method to fabricate densely populated, monodispersed cobalt atoms on a nitrogen‐doped graphene‐like carbon support is reported, and achieving a dramatically higher site fraction of Co atoms (≈15.3%) in the catalyst and demonstrating excellent electrocatalytic activity for both the oxygen reduction reaction and oxygen evolution reaction. The atomic dispersion and high site fraction of Co provide a large electrochemically active surface area of ≈105.6 m2 g−1, leading to very high mass activity for ORR (≈12.164 A mgCo−1 at 0.8 V vs reversible hydrogen electrode), almost 10.5 times higher than that of the state‐of‐the‐art benchmark Pt/C catalyst (1.156 A mgPt−1 under similar conditions). It also demonstrates an outstanding mass activity for OER (0.278 A mgCo−1). The Zn‐air battery based on this bifunctional catalyst exhibits high energy density of 945 Wh kgZn−1 as well as remarkable stability. In addition, both density functional theory based simulations and experimental measurements suggest that the CoN4 sites on the carbon matrix are the most active sites for the bifunctional oxygen electrocatalytic activity.

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Because of their exotic electronic properties and abundant active sites, two-dimensional (2D) materials have potential in various fields. Pursuing a general synthesis methodology of 2D materials and advancing it from the laboratory to industry is of great importance. This type of method should be low cost, rapid and highly efficient. Here, we report the high-yield synthesis of 2D metal oxides and hydroxides via a molten salts method. We obtained a high-yield of 2D ion-intercalated metal oxides and hydroxides, such as cation-intercalated manganese oxides (Na0.55Mn2O4·1.5H2O and K0.27MnO2·0.54H2O), cation-intercalated tungsten oxides (Li2WO4 and Na2W4O13), and anion-intercalated metal hydroxides (Zn5(OH)8(NO3)2·2H2O and Cu2(OH)3NO3), with a large lateral size and nanometre thickness in a short time. Using 2D Na2W4O13 as an electrode, a high performance electrochemical supercapacitor is achieved. We anticipate that our method will enable new path to the high-yield synthesis of 2D materials for applications in energy-related fields and beyond.

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2D materials have demonstrated good chemical, optical, electrical, and magnetic characteristics, and offer great potential in numerous applications. Corresponding synthesis technologies of 2D materials that are highquality, high-yield, low-cost, and time-saving are highly desired. Salt-assisted methods are emerging technologies that can meet these requirements for the fabrication of 2D materials. Herein, the recent process for the salt-assisted synthesis of 2D materials and their typical applications are summarized. First, the properties of salt crystals and molten salts are briefly introduced, and then some examples of 2D materials synthesis with the assistance of salt as well as their representative applications are presented. The underlying mechanisms of salts with different states on the formation of 2D morphology are discussed to aid in the rational design of synthetic route of 2D materials. At last, the challenges and future perspectives for salt-assisted methods are briefly described. This review provides guidance for the controllable synthesis of 2D materials based on the salt-assisted approaches.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201908486.MoO 3 , and LaNb 2 O 7 ), [14][15][16] layered double hydroxides (LDHs, e.g., Mg 6 Al 2 (OH) 16 CO 3 •4H 2 O), [17] hexagonal-boron nitride (h-BN), [2,18] transition metal halides (such as MoCl 2 and CrCl 3 ), [19] black phosphorus, [20] graphitic carbon nitride (g-C 3 N 4 ), [5] MXene (such as Ti 2 C and Ti 3 CN), [21][22][23][24][25] and clays (for instance, [(Mg 3 )(Si 2 O 5 ) 2 (OH) 2 ] and [(Al 2 )(Si 3 Al) O 10 (OH) 2 ]K). [19] Notably, many nonlayered structure species can also form 2D morphology with specific synthetic methods, largely expanding the 2D family (such as hexagonal-MoO 3 (h-MoO 3 ), hexagonal-WO 3 (h-WO 3 ), [15] transition metal nitrides (TMNs), [26,27] and transition metal phosphides (TMPs)). [28] To exploit the applications of 2D materials, the development of a synthetic method should be prioritized. Currently, synthesis processes of 2D materials could be divided into two categories, naming the top-down and bottom-up approaches. [29][30][31] Generally, exfoliation is the most common top-down method to produce monolayer or few-layer 2D materials. [19,32] Graphene was first prepared by mechanical exfoliation of highly oriented pyrolytic graphite with sellotape in 2004. [33] The exfoliation can weaken the interlayer Van der Waals force for bulk materials with layered crystal structures while maintain the covalent bonding in plane to produce monolayer or few-layer nanosheets. Although the productivity based on this method is limited due to the low efficiency, the exfoliation approach provides a new synthesis methodology for 2D materials. A series of studies on liquid exfoliation have been conducted by Coleman and co-workers. [19,34,35] By sonicating the bulk material in an appropriate solvent with similar interface energy, 2D material ink can be prepared. After the liq...

The multilayer relaxation at (100), (110), (111), (210), (211), (310), (311) and (331) surfaces of the fcc metals Cu, Ag, Au, Ni, Pd, Pt, Al and Pb are calculated using the modified embedded atom method. The 'anomalous' outward relaxation at Al (100), (111), Pt (111), and Cu (111) surfaces is described correctly. The relief of surface stress and tension on the relaxation is studied on (111), (100) and (110) surfaces. In general, the surface stress in the direction of the surface normal determines the relaxation direction except for the Al (110) surface. When the surface stress is negative, the surface relaxation is inward; otherwise, the relaxation is outward. An interesting result is that the surface tension does not always decrease after relaxation. The outward relaxation will induce the increase in surface tension while the inward relaxation induces the decrease in surface tension.

Molybdenum carbide (Mo 2 C) has been widely applied in energy conversion, electrocatalysis, and other electronic devices, but its nanostructure with certain morphology and porous structure is tough to control. In this work, 1D or 2D porous Mo 2 C nanostructures can be synthesized by carburizing cobalt-based zeolitic imidazolate framework (ZIF-67) cladding MoO 3 nanowires or nanosheets hybrid structure under high temperature. The obtained 2D porous Mo 2 C shows a low onset overpotential (η = 25 and 36 mV) and a small Tafel slope (40 and 47 mV dec −1 ) in 0.1 m HClO 4 and 0.1 m KOH as well as great stability. This work highlights a new strategy for the design and synthesis of porous nanostructure Mo 2 C electrocatalysts. and 1D nanowires. The approach is through carburizing cobalt or zinc-based zeolite-type metal-organic framework (MOF) (ZIF-67 or ZIF-8) cladding MoO 3 nanosheets or nanowires under high temperature. The resulting nanostructures are periodically porous, largely preserving the precursor morphology. The porous Mo 2 C materials may provide an exceptionally large number of active sites. For instance, 2D Mo 2 C nanosheets may show excellent catalytic performance for hydrogen evolution over a broad range of pH value (0.1 m HClO 4 and 0.1 m KOH), including a low onset overpotential (η = 25 and 36 mV vs RHE), a small Tafel slope (40 and 47 mV dec −1 ), and remarkable stability.

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