Reproducible SERS substrates manipulated by interparticle spacing and particle diameter of gold nano-island array using in-situ thermal evaporation.

Gold (Au) nano-island arrays were deposited on the glass substrate to fabricate surface-enhanced Raman scattering (SERS) substrates by in-situ thermal evaporation (deposited and annealed samples at the same time). The optimal SERS intensity deposited by various thicknesses and in-situ annealing temperatures of Au nano-island arrays would be investigated. The biomolecules (adenine) were dropped on the well-designed SERS substrate for precise and quantitative SERS detection. The characterization of Au nano-island arrays SERS substrate would be evaluated by scanning electron microscope (SEM) and Raman spectroscopy. The results showed that the optimal deposition thickness and annealing temperature of Au nano-island arrays SERS substrate is about 14 nm and 200 °C respectively, which can construct the smallest interparticle spacing (W)/ particle diameter (D) ratio and the lowest reflection (%) and transmittance (%) to form the strongest SERS intensity. Moreover, finite-difference time-domain (FDTD) simulation of the electromagnetic field distributions on Au nano-island arrays displays the similar trend with the experimental results. The 14 nm deposition with 200 °C in-situ annealing temperature would display the highest density of hot-spots by FDTD simulation. The reproducible Au nano-island arrays SERS substrates with tunable surface roughness, W/D ratio, and lower reflection and transmittance show promising potential for SERS detection of biomolecules, bacteria, and viruses.

Facile and Rapid Electrochemical Conversion of Ni into Ni(OH)2 Thin Film as the Catalyst for Direct Growth of Carbon Nanotubes on Ni Foam for Supercapacitors.

In this paper, a facile and rapid aqueous-based electrochemical technique was used for the phase conversion of Ni into Ni(OH)2 thin film. The Ni(OH)2 thin film was directly converted and coated onto the network surface of Ni foam (NF) via the self-hydroxylation process under alkaline conditions using a simple cyclic voltammetry (CV) strategy. The as-formed and coated Ni(OH)2 thin film on the NF was used as the catalyst layer for the direct growth of carbon nanotubes (CNTs). The self-converted Ni(OH)2 thin film is a good catalytic layer for the growth of CNTs due to the fact that the OH- of the Ni(OH)2 can be reduced to H2O to promote the growth of CNTs during the CVD process, and therefore enabling the dense and uniform CNTs growth on the NF substrate. This binder-free CNTs/NF electrode displayed outstanding behavior as an electric double-layer capacitor (EDLC) due to the large surface area of the CNTs, showing excellent specific capacitance values of 737.4 mF cm-2 in the three-electrode configuration and 319.1 mF cm-2 in the two-electrode configuration, at the current density of 1 mA cm-2 in a 6 M KOH electrolyte. The CNTs/NF electrode also displayed good cycling stability, with a capacitance retention of 96.41% after 10,000 cycles, and this the excellent cycling performance can be attributed to the stable structure of the direct growth of CNTs with a strong attachment to the NF current collector, ensuring a good mechanical and electrical connection between the NF collector and the CNTs.

Free-standing 3D core-shell architecture of Ni3S2@NiCoP as an efficient cathode material for hybrid supercapacitors.

The design and discovery of free-standing hybrid electrode materials with large absolute capacity and high cycling stability for energy storage become desirable and are still challenging. In this work, we demonstrate that the hybrid supercapacitor (HSC) device is assembled by 3D core-shell hierarchical nanorod arrays of Ni3S2@NiCoP nanocomposite for the first time. The Ni3S2@NiCoP nanocomposite is successfully synthesized through a facile stratagem containing hydrothermal process and the subsequent electrodeposition method. The 3D architecture of Ni3S2@NiCoP hybrid electrode composed of vertically aligned "hyperchannel" 1D Ni3S2 nanorods and highly conductive interconnected 2D nanosheets of NiCoP is beneficial to fast electron transfer kinetics, thus leading to enhancing the ionic and electronic conductivity, kinetics of redox reaction, and synergistic behavior of active species. The fabricated HSC device with Ni3S2@NiCoP electrode delivers outstanding areal capacity of 109 µAh cm-2 at a current density of 1 mA cm-2, brilliant energy density of 74.9 Wh kg-1 at a power density of 700 W kg-1, and prominent cyclic performance of 92% capacity retention even after 144-h floating test. This work demonstrates that the core-shell hierarchical nanorod arrays of Ni3S2@NiCoP can be viewed as one of the novel battery-type electrode materials for high-performance HSCs.

The Two-Dimensional Nanocomposite of Molybdenum Disulfide and Nitrogen-Doped Graphene Oxide for Efficient Counter Electrode of Dye-Sensitized Solar Cells.

In this study, we reported the synthesis of the two-dimensional (2D) nanocomposite of molybdenum disulfide and nitrogen-doped graphene oxide (MoS2/nGO) as a platinum-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy were used to examine the characteristics of the 2D nanocomposite of MoS2/nGO. The cyclic voltammetry (CV), electrochemical impedance spectra (EIS), and the Tafel polarization measurements were carried out to examine the electrocatalytic abilities. XPS and Raman results showed the 2D behaviors of the prepared nanomaterials. HRTEM micrographs showed the direct evidence of the 2D nanocomposite of MoS2/nGO. The results of electrocatalytic examinations indicated the MoS2/nGO owning the low charge transfer resistance, high electrocatalytic activity, and fast reaction kinetics for the reduction of triiodide to iodide on the electrolyte-electrode interface. The 2D nanocomposite of MoS2/nGO combined the advantages of the high specific surface of nGO and the plenty edge sites of MoS2 and showed the promoted properties different from those of their individual constituents to create a new outstanding property. The DSSC with MoS2/nGO nanocomposite CE showed a photovoltaic conversion efficiency (PCE) of 5.95 % under an illumination of AM 1.5 (100 mW/cm(2)), which was up to 92.2 % of the DSSC with the conventional platinum (Pt) CE (PCE = 6.43 %). These results reveal the potential of the MoS2/nGO nanocomposite in the use of low-cost, scalable, and efficient Pt-free CEs for DSSCs.

Enhanced Electrochemical Catalytic Efficiencies of Electrochemically Deposited Platinum Nanocubes as a Counter Electrode for Dye-Sensitized Solar Cells.

Platinum nanocubes (PtNCs) were deposited onto a fluorine-doped tin oxide glass by electrochemical deposition (ECD) method and utilized as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). In this study, we controlled the growth of the crystalline plane to synthesize the single-crystal PtNCs at room temperature. The morphologies and crystalline nanostructure of the ECD PtNCs were examined by field emission scanning electron microscopy and high-resolution transmission electron microscopy. The surface roughness of the ECD PtNCs was examined by atomic force microscopy. The electrochemical properties of the ECD PtNCs were analyzed by cyclic voltammetry, Tafel polarization, and electrochemical impedance spectra. The Pt loading was examined by inductively coupled plasma mass spectrometry. The DSSCs were assembled via an N719 dye-sensitized titanium dioxide working electrode, an iodine-based electrolyte, and a CE. The photoelectric conversion efficiency (PCE) of the DSSCs with the ECD PtNC CE was examined under the illumination of AM 1.5 (100 mWcm(-2)). The PtNCs in this study presented a single-crystal nanostructure that can raise the electron mobility to let up the charge-transfer impedance and promote the charge-transfer rate. In this work, the electrocatalytic mass activity (MA) of the Pt film and PtNCs was 1.508 and 4.088 mAmg(-1), respectively, and the MA of PtNCs was 2.71 times than that of the Pt film. The DSSCs with the pulse-ECD PtNC CE showed a PCE of 6.48 %, which is higher than the cell using the conventional Pt film CE (a PCE of 6.18 %). In contrast to the conventional Pt film CE which is fabricated by electron beam evaporation method, our pulse-ECD PtNCs maximized the Pt catalytic properties as a CE in DSSCs. The results demonstrated that the PtNCs played a good catalyst for iodide/triiodide redox couple reactions in the DSSCs and provided a potential strategy for electrochemical catalytic applications.

Low-Temperature Thermally Reduced Molybdenum Disulfide as a Pt-Free Counter Electrode for Dye-Sensitized Solar Cells.

A two-dimensional nanostructure of molybdenum disulfide (MoS2) thin film exposed layered nanosheet was prepared by a low-temperature thermally reduced (TR) method on a fluorine-doped tin oxide (FTO) glass substrate as a platinum (Pt)-free and highly electrocatalytic counter electrode (CE) for dye-sensitized solar cells (DSSCs). Thermogravimetric analysis (TGA) results show that the MoS2 sulfidization temperature was approximately 300 °C. X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) indicate that the stoichiometry and crystallization of MoS2 were more complete at higher temperatures; however, these temperatures reduce the number of edge-plane active sites in the short-range-order nanostructure. Accordingly, the DSSCs with 300 °C annealed TR-MoS2 CE exhibited an excellent photovoltaic conversion efficiency (PCE) of 6.351 %, up to 91.7 % of which is obtained using the conventional TD-Pt CE (PCE = 6.929 %). The temperature of thermal reaction and the molar ratio of reaction precursors were found to significantly influence the resulting stoichiometry and crystallization of MoS2 nanosheets, thus affecting DSSCs' performance.

Thermally conductive and electrically insulating epoxy nanocomposites with thermally reduced graphene oxide-silica hybrid nanosheets.

We herein report on the preparation of epoxy nanocomposites, which had enhanced thermal conductivities but were still electrical insulators, incorporating hybrid nanosheets (NSs) with sandwich structures composed of thermally reduced graphene oxide (TRGO) and silica. The silica layer covered the surface of the TRGO, hindering electrical conduction and effectively forming a 3D phonon transport channel that had a unique effect on the electrical and thermal properties of the epoxy matrix. A 1 wt% TRGO-silica NS epoxy nanocomposite maintained an electrical resistivity of 2.96 × 10(11)Ω cm, and its thermal conductivity was 0.322 W m(-1) K(-1), which is 61% higher than the conductivity of an epoxy nanocomposite without TRGO-silica NSs (0.2 W m(-1) K(-1)).

Direct synthesis of platelet graphitic-nanofibres as a highly porous counter-electrode in dye-sensitized solar cells.

We synthesized platelet graphitic-nanofibres (GNFs) directly onto FTO glass and applied this forest of platelet GNFs as a highly porous structural counter-electrode in dye-sensitized solar cells (DSSCs). We investigated the electrochemical properties of counter-electrodes made from the highly porous structural GNFs and the photoconversion performance of the cells made with these electrodes.

A hybrid nanostructure of platinum-nanoparticles/graphitic-nanofibers as a three-dimensional counter electrode in dye-sensitized solar cells.

We directly synthesized a platinum-nanoparticles/graphitic-nanofibers (PtNPs/GNFs) hybrid nanostructure on FTO glass. We applied this structure as a three-dimensional counter electrode in dye-sensitized solar cells (DSSCs), and investigated the cells' photoconversion performance.

Preparation and properties of a carbon nanotube-based nanocomposite photoanode for dye-sensitized solar cells.

This study fabricates dye-sensitized solar cells (DSSCs) based on TiO(2)/multi-walled carbon nanotube (MWCNT) nanocomposite photoanodes obtained by the modified acid-catalyzed sol-gel procedure. Results show that incorporating MWCNTs into a TiO(2)-based electrode efficiently improves the physicochemical properties of the solar cell. The results of dye adsorption and cell performance measurements indicate that introducing MWCNTs would improve the roughness factor (from 834 to 1267) of the electrode and the charge recombination of electron/hole (e(-)/h(+)) pairs. These significant changes could lead to higher adsorbed dye quantities, photocurrent and DSSC cell performance. Nevertheless, a higher loading of MWCNTs causes light-harvesting competition that affects the light adsorption of the dye-sensitizer, and consequently reduces the cell efficiency. This study suggests an optimum MWCNT loading in the electrode of 0.3 wt%, and proposes a sol-gel synthesis procedure as a promising method of preparing the TiO(2)-based nanocomposite.