The hydrogen evolution reaction in an alkaline environment using a non‐precious catalyst with much greater efficiency represents a critical challenge in research. Here, a robust and highly active system for hydrogen evolution reaction in alkaline solution is reported by developing MoS2 nanosheet arrays vertically aligned on graphene‐mediated 3D Ni networks. The catalytic activity of the 3D MoS2 nanostructures is found to increase by 2 orders of magnitude as compared to the Ni networks without MoS2. The MoS2 nanosheets vertically grow on the surface of graphene by employing tetrakis(diethylaminodithiocarbomato)molybdate(IV) as the molybdenum and sulfur source in a chemical vapor deposition process. The few‐layer MoS2 nanosheets on 3D graphene/nickel structure can maximize the exposure of their edge sites at the atomic scale and present a superior catalysis activity for hydrogen production. In addition, the backbone structure facilitates as an excellent electrode for charge transport. This precious‐metal‐free and highly efficient active system enables prospective opportunities for using alkaline solution in industrial applications.
In this study, robust nanoscale superamphiphobic (SAP) copper (Cu) sheet surfaces are obtained with an exceptionally simple and environmentally friendly technique. Copper oxide nanostructures are imparted onto the Cu sheet surface by a facile treatment of the surfaces with hot de-ionized water (%80°C) for different time periods. A morphological transformation starting from cube-like nanostructures associated with Cu 2 O to leaf-like nanostructures of CuO with the progress in treatment time is observed. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energydispersive X-ray spectroscopy (EDS), and laser scanning microscopy (LSM) analysis confirm the formation of copper oxide nanostructures. Consequently, the wetting properties of the treated Cu sheet surfaces toward water and organic liquids is varied after the surface energy reduction of the nanostructures with long chain fluorocarbon molecules of 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (PFDCS). The leaf-like nanostructured CuO surfaces demonstrate SAP properties with a water contact angle (CA) as high as 160°and organic liquid CAs of around 150°. The robustness of the obtained SAP Cu sheet surface is confirmed after being exposed to a stream of both water and organic liquids, annealed under various temperatures in ambient environment, and ultra-sonicated in acetone for various time periods.
Working gas pressure during sputter deposition can significantly affect the conformality of a thin film when it is grown on a nanostructured surface. In this study, we fabricated core-shell nanostructured photodetectors, where n-type In2S3 nanorod arrays (core) were coated with p-type CuInS2 (CIS) films (shell) at relatively low and high Ar gas pressures. In2S3 nanorods were prepared by glancing angle deposition (GLAD) technique using a thermal evaporator unit. CIS films were deposited by RF sputtering at Ar pressures of 2.7x10-2 mbar (high pressure sputtering, HIPS) and 7.3x10-3 mbar (low pressure sputtering, LPS). The morphological characterization was carried out by means of SEM. The photocurrent measurement was conducted under 1.5 AM Sun under no bias. Nanostructured photodetectors of HIPS-CIS/GLAD-In2S3 (i.e. HIPS-GLAD) were shown to demonstrate enhanced photoresponse with a photocurrent value of 98 μA, which is about ∼230% higher than that of LPS-GLAD devices. The enhancement originates from the improved core-shell structure achieved by more conformal coating of the CIS shell. In addition, the results were compared to their counterpart thin-film devices incorporating an In2S3 film coated either with HIPS or LPS CIS layer. Nanorod devices with high and low pressure CIS films showed photocurrent values ∼20 times and ∼ 19 times higher compared to those of high and low pressure film devices, respectively. This finding can be explained by the higher light absorption property of nanorods, and the reduced inter-electrode distance as a result of core-shell structure, which allows the effective capture of the photo-generated carriers. Therefore, the results of this work can pave way to the development of high photoresponse core-shell semiconductor devices fabricated by physical vapor deposition techniques.
In this study, the authors fabricated high performance core–shell nanostructured flexible photodetectors on a polyimide substrate of Kapton. For this purpose, p-type copper indium gallium selenide (CIGS) nanorod arrays (core) were coated with aluminum doped zinc oxide (AZO) films (shell) at relatively high Ar gas pressures. CIGS nanorods were prepared by glancing angle deposition (GLAD) technique using radio frequency (RF) magnetron sputtering unit at room temperature. AZO films were deposited by RF sputtering at Ar pressures of 1.0×10−2 mbar (high pressure sputtering) for the shell and at 3.0×10−3 mbar (low pressure sputtering) to create a top contact. As a comparison, the authors also fabricated conventional planar thin film devices incorporating CIGS film of similar material loading to that of CIGS nanorods. The morphological characterization was carried out by field-emission scanning electron microscope. The photocurrent measurement was conducted under 1.5 AM sun at zero electrical biasing, where CIGS devices were observed to absorb in the ultraviolet-visible-near infrared spectrum. GLAD core–shell nanorod photodetectors were shown to demonstrate enhanced photoresponse with an average photocurrent density values of 4.4, 3.2, 2.5, 3.0, and 2.5 μA/cm2 for bending angles of 0°, 20°, 40°, 60°, and 80°, respectively. These results are significantly higher than the photocurrent of most of the flexible photodetectors reported in the literature. Moreover, our nanorod devices recovered their photoresponse after several bending experiments that indicate their enhanced mechanical durability. On the other hand, thin film devices did not show any notable photoresponse. Improved photocurrent of CIGS nanorod devices is believed to be due to their enhanced light trapping property and the reduced interelectrode distance because of the core–shell structure, which allows the efficient capture of the photo-generated carriers. In addition, enhanced mechanical durability is achieved by the GLAD nanorod microstructure on a flexible substrate. This approach can open a new strategy to boost the performance of flexible photodetectors and wearable electronics.
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