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Earth‐abundant and highly‐efficient electrocatalysts for oxygen evolution reaction (OER) are urgently desired to realize the large‐scale storage and conversion of renewable energies. In this work, we develop a hierarchical porous electrocatalyst structure utilizing Ni(OH)2 nanosheets directly synthesized on Ni foam as the conductive and interconnected supports. By coupling with amorphous Ni−B nanoparticles, this hybrid catalyst exhibits dramatically enhanced electrocatalytic activities and durabilities towards OER. In specific, along with the optimized Ni−B loading, this catalyst requires only an impressively small overpotential of 300 mV to drive a current density of 100 mA cm−2 for oxygen evolution in 1 M KOH electrolyte. Meanwhile, it also yields a small Tafel slope of 49 mV dec−1 and a superior long‐term stability. All these results evidently indicate that the hierarchical hybridization of Ni−B with Ni(OH)2 on Ni foam can effectively synergize the oxygen evolution, opening up a new vista for designing high‐performance transition metal‐based nanostructures in the field of electrochemical water splitting. A hierarchical porous electrocatalyst structure utilizing Ni(OH)2 nanosheets directly synthesized on Ni foam as the conductive and interconnected supports is developed for the deposition of Ni−B nanoparticles by using the facile dip‐coating method. This synergistic hybrid electrocatalyst system configured of Ni−B nanoparticles, Ni(OH)2 nanosheets and Ni foam can exhibit dramatically electrocatalytic activities and superior long‐term stabilities towards oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) nanomaterials have recently attracted considerable attention due to their promising applications in next-generation electronics and optoelectronics. In particular, the large-scale synthesis of high-quality 2D materials is an essential requirement for their practical applications. Herein, we demonstrate the wafer-scale synthesis of highly crystalline and homogeneous monolayer WS2 by an enhanced chemical vapor deposition (CVD) approach, in which precise control of the precursor vapor pressure can be effectively achieved in a multi-temperature zone horizontal furnace. In contrast to conventional synthesis methods, the obtained monolayer WS2 has excellent uniformity both in terms of crystallinity and morphology across the entire substrate wafer grown (e.g., 2 inches in diameter), as corroborated by the detailed characterization. When incorporated in typical rigid photodetectors, the monolayer WS2 leads to a respectable photodetection performance, with a responsivity of 0.52 mA/W, a detectivity of 4.9 × 109 Jones, and a fast response speed (< 560 μs). Moreover, once fabricated as flexible photodetectors on polyimide, the monolayer WS2 leads to a responsivity of up to 5 mA/W. Importantly, the photocurrent maintains 89% of its initial value even after 3,000 bending cycles. These results highlight the versatility of the present technique, which allows its applications in larger substrates, as well as the excellent mechanical flexibility and robustness of the CVD-grown, homogenous WS2 monolayers, which can promote the development of advanced flexible optoelectronic devices. [ABSTRACT FROM AUTHOR]

To date, wafer‐scale synthesis of two‐dimensional (2D) materials are well achieved by chemical vapor deposition, but the obtained monolayers typically have multidomains with electrical and optoelectronic properties affected by grain boundaries and domain sizes. When these 2D materials are used as the growth templates, these boundaries would also provide unknown influences to the successive heterostructure formation for extended applications. Here, for the first time, direct visualization of grain boundaries in monolayer WS2 film can be realized by the growth of CdS nanoparticles. Specifically, CdS is found to first preferentially nucleate and form as nanoparticle chains along WS2 grain boundaries in a random manner, independent of the grain boundary characteristics. Due to electron scattering and type II band alignment at the WS2–CdS heterojunction, WS2 reduces in its mobility while becoming enhanced in its electron concentration. Notably, the WS2–CdS heterostructure also yields improved carrier separation and collection for the photodetection performance enhancement. All these results can facilitate the detailed evaluation of crystalline grains‐related information of 2D materials and provide thorough understanding on the effect of these overgrown CdS on underlying WS2 monolayers, being extremely important to further optimize and enable their functionalities for advanced device applications. Grain boundaries in chemical vapor deposited monolayer WS2 induce the growth of CdS nanoparticle chains there, making the grain boundaries visible. This overgrowth of CdS nanoparticles at the WS2 grain boundaries then leads to the formation of a type II heterojunction, which can reduce the carrier mobility while enhancing the photodetection performance of WS2. [ABSTRACT FROM AUTHOR]

Recently, due to the possibility of thinning down to the atomic thickness to achieve exotic properties, layered materials have attracted extensive research attention. In particular, PbI 2 , a kind of layered material, and its perovskite derivatives, CH 3 NH 3 PbI 3 (i.e., MAPbI 3 ), have demonstrated impressive photoresponsivities for efficient photodetection. Herein, the synthesis of large-scale, high-density, and freestanding PbI 2 nanosheets is demonstrated by manipulating the microenvironment during physical vapor deposition. In contrast to conventional two-dimensional (2D) growth along the substrate surface, the essence here is the effective nucleation of microplanes with different angles relative to the in-plane direction of underlying rough-surfaced substrates. When configured into photodetectors, the fabricated device exhibits a photoresponsivity of 410 mA W -1 , a detectivity of 3.1 × 10 11 Jones, and a fast response with the rise and decay time constants of 86 and 150 ms, respectively, under a wavelength of 405 nm. These PbI 2 nanosheets can also be completely converted into MAPbI 3 materials via chemical vapor deposition with an improved photoresponsivity up to 40 A W -1 . All these performance parameters are comparable to those of state-of-the-art layered-material-based photodetectors, revealing the technological potency of these freestanding nanosheets for next-generation high-performance optoelectronics., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)