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We demonstrate, for the first time, a new method of fabricating hybrid MoS/poly(ethyleneimine)-modified graphene oxide (PEI-GO) composites assembled through electrostatically charged interaction between the negatively charged MoS nanosheets and positively charged PEI-GO in an aqueous solution. The GO can not only improve the electronic conductivity of the MoS/PEI-GO composites, leading to an excellent charge-transfer network, but also hamper the restacking of MoS nanosheets. The composition ratios between MoS and PEI-GO were also optimized with the highest specific capacitance of 153.9 F g where 96.0% of the initial specific capacitance remains after 6800 cycles. The specific capacitance of only 117.5 F g was observed for the pure MoS nanosheets, and 68.2% of the initial specific capacitance was achieved after 5000 cycles. The excellent electrochemical performance of the hybrid MoS/PEI-GO composites was demonstrated by establishing an asymmetric supercapacitor with a MoS/PEI-GO-based negative electrode and an activated-carbon positive electrode. The asymmetric supercapacitor provided a maximum capacitance of 42.9 F g, and 93.1% of the initial capacitance was maintained after 8000 cycles. Furthermore, a MoS/PEI-GO//activated-carbon asymmetric supercapacitor delivered an energy density of 19.3 W h kg and a power density of 4500 W kg, indicating the potential of the hybrid MoS/PEI-GO composites in electrochemical energy storage applications.

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inexhaustible features. It is well known that solar cells can absorb photons from sunlight, resulting in electron-hole pairs, which would be segmented by the built-in electric field at the interface of two different semiconductors. As a result, the electric current would be produced and the solar energy is converted to electric energy. Up to now, the development of solar cells can be roughly categorized into four types based on their basic forming materials. For the first type, solar cells are mostly made of single crystal silicon, polycrystalline silicon, and noncrystalline silicon. The configuration of these cells is normally based on the p-i-n junction, showing a superior photoelectrical conversion efficiency (PCE) up to about 25.6% (Panasonic, Japan). [33] However, the manufacturing cost is very high due to complicated crafting and high purity demand. Furthermore, the by-product of silicon is hazardous to the environment. Scientists thereby keep looking for alternatives that can offer even better efficiency and are environmentally friendly. The second type refers to the inorganic solar cells that are made of CdS, CdTe, GaAs, and CuIn(Ga)Se films. The highest PCE of such type of cells were reported to be 21.7% (ZSW, Germany). [33] Although this value is close to the performance of Si-based solar cells, the use of rare elements (Ga, Te, Se) and highly toxic Cd makes it to be hard for further developments. The third type of solar cells are the organic photovoltaic cells (OPCs), which are made of magnesium phthalocyanine (MgPc)-based materials, in which the electron-hole pairs are stimulated by the organic p-i-n junction, giving the PCE of about ≈10.6%. [34] In addition to this unsatisfactory PCE, OPCs were also reported to have a short lifetime due to their poor stability. The fourth type of solar cells is the dye-sensitized solar cells (DSSCs), which are typically consisted of organic dyes, TiO 2 electron absorber layer, and I − /I 3 − -based liquid electrolyte. The highest PCE of DSSCs only reach about 13%, [35] and the leakage of liquid electrolyte is still unsolved. By considering all the factors mentioned above, currently, the Si-based solar cells still dominate the market over the other three types.Recently, the emerging organic-inorganic metal halide perovskite (CH 3 NH 3 PbI 3 ) solar cells (PSCs) have challenged this monopoly status. Owing to the strong absorption coefficient, long charge diffusion length, fast charge migration rate, and small excitation binding energy (50 meV), the PCE of PSCs has been recently enhanced from 3.8% to 22.1%, [36] In recent years, organic-inorganic halide perovskites have emerged as prospective materials for high-efficiency, inexpensive, and environmentally friendly perovskite solar cells (PSCs). Despite their superiority in synthesizing route, the poor stability of PSCs with regard to humidity, heat, UV radiation, and oxygen limits their applications. Moreover, the toxicity of perovskite films and suitable ways to achieve large-area production need to be taken into accou...

Transition metal single-atom catalysts (SACs) are currently a hot area of research in the field of electrocatalytic oxygen reduction reaction (ORR). In this review, the recent advances in transition metal single-atom supported by 2D materials as catalysts for ORR with high performance are reported. Due to their large surface area, uniformly exposed lattice plane, and adjustable electronic state, 2D materials are ideal supporting materials for exploring ORR active sites and surface reactions. The rational design principles and synthetic strategies of transition metal SACs supported by 2D materials are systematically introduced while the identification of active sites, their possible catalytic mechanisms as well as the perspectives on the future of transition metal SACs supported by 2D materials for ORR applications are discussed. Finally, according to the current development trend of ORR catalysts, the future opportunities and challenges of transition metal SACs supported by 2D materials are summarized.

Here we report a novel solid-state ECL sensor for ultrasensitive sensing of glutathione (GSH) based on ferrocyanide-ferricyanide redox couple (Fe(CN)6(3-/4-)) induced electrochemiluminescence (ECL) amplification of carbon dots (C-dots). The electropolymerization of C-dots and (11-pyrrolyl-1-yl-undecyl) triethylammonium tetrafluoroborate (A2) enabled immobilization of the hydrophilic C-dots on the surface of glassy carbon electrode (GCE) perfectly, while the excellent conductivity of polypyrrole was exploited to accelerate electron transfer between them. The Fe(CN)6(3-/4-) can expeditiously convert the C-dots and S2O8(2-) to C-dot(•-) and SO4(•-), respectively. High yields of the excited state C-dots (C-dots*) were obtained, and a ∼10-fold ECL amplification was realized. The C-dots* obtained through the recombination of electron-injected and hole-injected processes may be impeded due to the interference of GSH to K2S2O8. Therefore, the constructed sensor for GSH showed a detection limit down to 54.3 nM (S/N = 3) and a wide linear range from 0.1-1.0 μM with a correlation coefficient of 0.997.