Layered two-dimensional (2D) nanomaterials such as graphene are a conceptually new class of materials that offers new access to low-dimensional physics. [1][2][3][4] Besides wellknown graphene, inorganic graphene analogues (IGAs) [5] such as layered transition metal dichalcogenides (e.g., MoS 2 and WS 2 ) [5][6][7] and boron nitride (BN) [8] have been attracting rapidly increasing attention in the past few years. These IGAs were expected to exhibit unique properties and have great potential in applications like transistors, [9][10][11] energy storage, [12,13] thermal conductors, [14] and topological insulators.[15]Moreover, IGAs like MoS 2 and WS 2 have intrinsic band gap and high mobility, and may even compete with graphene in certain fields. [9] However, investigations on IGAs have been significantly hindered by the practical difficulties in the preparation and assembly of these 2D nanomaterials.Only a few approaches to obtain few-layered IGAs have been reported. Mechanical exfoliation [1,16] was first used to obtain layered IGAs from their bulk materials. [9,17] Other approaches that are being explored include chemical synthesis [6,18,19] and liquid exfoliation.[5] Coleman et al. recently reported a surfactant-free liquid-exfoliation method which can produce few-layered nanosheets of IGAs dispersed in various organic solvents.[5] Thermodynamic analysis suggested that, because of the high surface energy of IGAs, the best solvents are likely to have high boiling points. [20,21] Using nonvolatile solvents makes it difficult to process IGAs into devices, [21,22] due to the difficulties in the removal of solvent and the occurrence of aggregation during the slow solvent evaporation. To date, liquid exfoliation of layered MoS 2 and WS 2 in volatile solvent has met with very limited success.Herein we demonstrate a versatile and scaleable mixedsolvent strategy for liquid exfoliation of IGAs, including WS 2 , MoS 2 , and BN, in volatile solvents. By choosing solvents with appropriate composition, highly stable IGA suspensions can be obtained in low-boiling solvent mixtures, which can then be easily used in further applications.The dispersion of nanomaterials in liquids can be partially predicted by the theory of Hansen solubility parameters (HSP), [5,23,24] which is a semi-empirical correlation developed to explain dissolution behavior.[23] Three HSP parameters are used to describe the character of a solvent or material: d D , d P , and d H , which are the dispersive, polar, and hydrogen-bonding solubility parameters, respectively. The dissolution process is one of adaptation between the HSP parameters of solvents and solutes. The HSP distance R a is used to evaluate the level of adaptation [Eq. (1)].The smaller the R a value, the higher the expected solubility. If the HSP parameters of a nanomaterial are known, the R a value can be used as a guide for finding a single efficient solvent for its dispersion.Besides single-component solvents, HSP theory can be also applied to solvent mixtures, in which each of the three HS...

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Simultaneous realization of improved activity, enhanced stability, and reduced cost remains a desirable yet challenging goal in the search of electrocatalysis oxygen evolution reaction (OER) in acid. Herein, we report a novel strategy to prepare iridium single-atoms (Ir-SAs) on ultrathin NiCo2O4 porous nanosheets (Ir–NiCo2O4 NSs) by the co-electrodeposition method. The surface-exposed Ir-SAs couplings with oxygen vacancies (VO) exhibit boosting the catalysts OER activity and stability in acid media. They display superior OER performance with an ultralow overpotential of 240 mV at j = 10 mA cm–2 and long-term stability of 70 h in acid media. The TOFs of 1.13 and 6.70 s–1 at an overpotential of 300 and 370 mV also confirm their remarkable performance. Density functional theory (DFT) calculations reveal that the prominent OER performance arises from the surface electronic exchange-and-transfer activities contributed by atomic Ir incorporation on the intrinsic VO existed NiCo2O4 surface. The atomic Ir sites substantially elevate the electronic activity of surface lower coordinated Co sites nearby VO, which facilitate the surface electronic exchange-and-transfer capabilities. With this trend, the preferred H2O activation and stabilized *O have been reached toward competitively lower overpotential. This is a generalized key for optimally boosting OER performance.

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Layered two-dimensional (2D) nanomaterials such as graphene are a conceptually new class of materials that offers new access to low-dimensional physics. [1][2][3][4] Besides wellknown graphene, inorganic graphene analogues (IGAs) [5] such as layered transition metal dichalcogenides (e.g., MoS 2 and WS 2 ) [5][6][7] and boron nitride (BN) [8] have been attracting rapidly increasing attention in the past few years. These IGAs were expected to exhibit unique properties and have great potential in applications like transistors, [9][10][11] energy storage, [12,13] thermal conductors, [14] and topological insulators. [15] Moreover, IGAs like MoS 2 and WS 2 have intrinsic band gap and high mobility, and may even compete with graphene in certain fields. [9] However, investigations on IGAs have been significantly hindered by the practical difficulties in the preparation and assembly of these 2D nanomaterials.Only a few approaches to obtain few-layered IGAs have been reported. Mechanical exfoliation [1,16] was first used to obtain layered IGAs from their bulk materials. [9,17] Other approaches that are being explored include chemical synthesis [6,18,19] and liquid exfoliation. [5] Coleman et al. recently reported a surfactant-free liquid-exfoliation method which can produce few-layered nanosheets of IGAs dispersed in various organic solvents. [5] Thermodynamic analysis suggested that, because of the high surface energy of IGAs, the best solvents are likely to have high boiling points. [20,21] Using nonvolatile solvents makes it difficult to process IGAs into devices, [21,22] due to the difficulties in the removal of solvent and the occurrence of aggregation during the slow solvent evaporation. To date, liquid exfoliation of layered MoS 2 and WS 2 in volatile solvent has met with very limited success.Herein we demonstrate a versatile and scaleable mixedsolvent strategy for liquid exfoliation of IGAs, including WS 2 , MoS 2 , and BN, in volatile solvents. By choosing solvents with