Memristor, which had been predicted a long time ago (Chua, L. O. IEEE Trans. Circuit Theory 1971, 18, 507), was recently invented (Strukov, D. B.; et al. Nature 2008, 453, 80). The introduction of a memristor is expected to open a new era for nonvolatile memory storage, neuromorphic computing, digital logic, and analog circuit. Furthermore, several breakthroughs were made for memristive phenomena and transistors with single-layer MoS2 (Sangwan, V. K.; et al. Nat. Nanotechnol. 2015, 10, 403. van der Zande, A. M.; et al. Nat. Mater. 2013, 12, 554. Liu, H.; et al. ACS Nano 2014, 8, 1031. Bessonov, A. A.; et al. Nat. Mater. 2015, 14, 199. Yuan, J.; et al. Nat. Nanotechnol. 2015, 10, 389). Herein, we demonstrate that 2H phase of bulk MoS2 possessed an ohmic feature, whereas 1T phase of exfoliated MoS2 nanosheets exhibited a unique memristive behavior due to voltage-dependent resistance change. Furthermore, an ideal odd-symmetric memristor with odd-symmetric I-V characteristics was successfully fabricated by the 1T phase MoS2 nanosheets via combining two asymmetric switches antiserially.

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In black and white: The hydrogenation of TiO(2) can extend its optical absorption into the visible and infrared region and change its color from white to black. Furthermore, the hydrogenated black TiO(2) exhibits excellent photocatalytic activity for the splitting of water to yield H(2).

Carbon materials, with their diverse allotropes, have played significant roles in our daily life and the development of material science. Following 0D C60 and 1D carbon nanotube, 2D graphene materials, with their distinctively fascinating properties, have been receiving tremendous attention since 2004. To fulfill the efficient utilization of 2D graphene sheets in applications such as energy storage and conversion, electrochemical catalysis, and environmental remediation, 3D structures constructed by graphene sheets have been attempted over the past decade, giving birth to a new generation of graphene materials called 3D graphene materials. This review starts with the definition, classifications, brief history, and basic synthesis chemistries of 3D graphene materials. Then a critical discussion on the design considerations of 3D graphene materials for diverse applications is provided. Subsequently, after emphasizing the importance of normalized property characterization for the 3D structures, approaches for 3D graphene material synthesis from three major types of carbon sources (GO, hydrocarbons and inorganic carbon compounds) based on GO chemistry, hydrocarbon chemistry, and new alkali-metal chemistry, respectively, are comprehensively reviewed with a focus on their synthesis mechanisms, controllable aspects, and scalability. At last, current challenges and future perspectives for the development of 3D graphene materials are addressed.

The current state-of-the-art of the synthesis, stabilization and applications of metallic 1T-phase MoS2: how it comes and where to go.

The dye-sensitized solar cell (DSSC) plays a leading role in third generation photovoltaic devices. Platinum-loaded conducting glass has been widely exploited as the standard counter electrode (CE) for DSSCs. However, the high cost and the rarity of platinum limits its practical application in DSSCs. This has promoted large interest in exploring Pt-free CEs for DSSCs. Very recently, graphene, which is an atomic planar sheet of hexagonally arrayed sp 2 carbon atoms, has been demonstrated to be a promising CE material for DSSCs due to its excellent conductivity and high electrocatalytic activity. This article provides a mini review of graphene-based CEs for DSSCs. Firstly, the fabrication and performance of graphene film CE in DSSCs are discussed. Secondly, DSSC counter electrodes made from graphene-based composite materials are evaluated. Finally, a brief outlook is provided on the future development of graphene-based materials as prospective counter electrodes for DSSCs.

Graphene, a two-dimensional carbon sheet, [1] has attracted great interest due to its unique properties. [2,3] To explore its practical applications, large-scale synthesis with controllable integration of individual graphene sheets is essential. To date, numerous approaches have been developed for graphene synthesis, including mechanical cleavage, [1] epitaxial growth, [4] and chemical vapor deposition. [5] All of those techniques are used to prepare flat graphene sheets on a substrate. Chemical exfoliation of graphite has been applied to prepare graphene oxide solutions and graphene-based composite materials. [6,7] Recently, tuning graphene shapes is attracting much attention. [8][9][10][11][12][13][14][15][16] Cheng and co-workers synthesized graphene foam using porous Ni foam as a template for the CVD growth of graphene, followed by etching away the Ni skeleton. [8] The graphene foam consists of an interconnected flexible network of graphene as the fast transport channel of charge carriers for high electrical conductivity. Ruoff et al. prepared porous graphene paper from microwave exfoliated graphene oxide by KOH activation. [9] The porous graphene, which has an ultra-high surface area and a high electrical conductivity, was exploited for supercapacitor cells, leading to high values of gravimetric capacitance and energy density. Feng, Müllen, and co-workers synthesized hierarchical macro-and mesoporous graphene frameworks (GFs). [10][11][12] The GFs exhibited excellent performance for electrochemical capacitive energy storage. Yu et al. [13] and Qu et al. [14] fabricated graphene tubes that could be selectively functionalized for desirable applications. Choi et al. synthesized macroporous graphene using polystyrene colloidal particles as sacrificial templates in graphene oxide suspension, [15] and the pore sizes can be tuned by controlling template particle size. [16] These important results represent a significant topic-tuning the properties of graphene sheets by controlling their shapes. However, it is still a challenge to synthesize three-dimensional graphene (3D) with a desirable shape.Herein, we develop a novel strategy for the synthesis of a new type of graphene sheet with a 3D honeycomb-like structure by a simple reaction between Li 2 O and CO. Furthermore, these graphene sheets exhibited excellent catalytic performance as a counter electrode for dye-sensitized solar cells (DSSCs) with an energy conversion efficiency as high as 7.8 %, which is comparable to that of an expensive platinum electrode.Li 2 O is widely exploited as a promoter in catalysts to inhibit carbon formation. [17] However, this general principle is challenged by this work, in which Li 2 O is used to react with CO to form graphene-structured carbon [Eq. (1)]This strategy is supported by our thermodynamic calculations: The Gibbs free energy change is negative, indicating that this reaction is thermodynamically favorable ( Figure S1 in the Supporting Information). The negative enthalpy change (DH 298 = À397.5 kJ mol À1 ) suggests it is a...

Li3N is a potential H2 storage material due to its high theoretical H2 capacity (10.4 wt %). A critical potential issue regarding this N-based storage material is the generation of NH3, which consumes some H2 and also constitutes a poison for the downstream processes. In this Letter, by using the temperature-programmed decomposition of a two-layer material (LiNH2 and LiH), we demonstrate that NH3 produced via the decomposition of LiNH2 is completely captured by LiH even at very short contact times (25 ms) with the carrier gas. This ultrafast reaction between NH3 and LiH inhibits NH3 formation during the hydrogenation of Li3N and also prevents the NH3 generated during the dehydrogenation of the hydrogenated Li3N to escape into the H2 stream. However, if the hydrogenated Li3N was previously exposed to the atmosphere, some NH3 could escape into the H2 stream during the H2 desorption, due to the partial oxidation of LiH by the water present in air.