Stevin S. Pramana

A cuprous oxide–reduced graphene oxide (Cu2O–rGO) composite photocatalyst for hydrogen generation : employing rGO as an electron acceptor to enhance the photocatalytic activity and stability of Cu2O

Photocorrosion, that causes rapid deactivation of Cu(2)O photocatalysts, was addressed by incorporating this oxide in a composite with reduced graphene oxide which acts as an electron acceptor to extract photogenerated electrons from Cu(2)O. Cu(2)O-rGO composite engineering also allows enhancing significantly photocatalytic activities of Cu(2)O for H(2) generation.

Copper molybdenum sulfide: a new efficient electrocatalyst for hydrogen production from water

A new inorganic solid state electrocatalyst for the hydrogen evolution reaction (HER) is reported. Highly crystalline layered ternary sulfide copper-molybdenum-sulfide (Cu2MoS4) was prepared by a simple precipitation method from CuI and [MoS4]2− precursors. In aqueous solution and over a wide pH range (pH 0 to 7), this Cu2MoS4 showed very good catalytic activity for HER with an overvoltage requirement of only ca. 135 mV and an apparent exchange current density of 0.040 mA cm−2 (Tafel slope of ca. 95 mV per decade was found irrespective of the pH value). This Cu2MoS4 catalyst was found to be stable during electrocatalytic hydrogen generation. Therefore, it represents an attractive alternative to platinum.

Nanoweb anodes composed of one-dimensional, high aspect ratio, size tunable electrospun ZnFe2O4 nanofibers for lithium ion batteries

Nanowebs consisting of interwoven ZnFe2O4 nanofibers are synthesized by a simple electrospinning technique, to be employed as an environmentally friendly anode in lithium ion batteries. Effect of precursor viscosity on the growth mechanism of electrospun ZnFe2O4 nanofibers (ZFO-NF) and ZnFe2O4 nanorods (ZFO-NR) is studied by microscopy and diffraction techniques. Structural characterization by powder X-ray diffraction, FESEM and HRTEM studies evaluates the single phase nature of ZnFe2O4, which consists of 11(3) nm nanocrystals that self-agglomerate to form nanofibers after thermal treatment. FESEM micrographs depict the self-assembly of electrospun ZnFe2O4 nanofibers into intertwined porous nanowebs with a continuous framework. Benefitting from the one-dimensional functional nanostructured architecture, the application of electrospun nanowebs with ZnFe2O4 nanofiber (ZFO-NF) anodes in lithium ion batteries exhibits excellent cyclability and retains a reversible capacity of 733(10) mAh g−1 up to 30 cycles at 60 mA g−1 as compared to ZnFe2O4 nanorods (ZFO-NR) with a capacity of ∼200 mAh g−1. In addition, the importance of providing electronic wiring during lithiation/delithiation, especially in prolonged cycling, is emphasized.

In situ photo-assisted deposition of MoS2 electrocatalyst onto zinc cadmium sulphide nanoparticle surfaces to construct an efficient photocatalyst for hydrogen generation

We reported herein a facile and scalable preparation process for MoS(2)-decorated Zn(x)Cd(1-x)S hybrid photocatalysts for hydrogen generation. Zn(x)Cd(1-x)S nanopowder was first prepared from commercially available precursors employing a solution based process. MoS(2) hydrogen evolution reaction catalyst was then loaded onto the Zn(x)Cd(1-x)S nanopowder via a photo-assisted deposition process which employed mild conditions (room temperature, atmospheric pressure and visible light illumination). Thus, this process represents an important advantage in the large scale production of semiconductor/MoS(2) hybrid photocatalysts in comparison to the conventional method relying on thermal decomposition of (NH(4))(2)[MoS(4)] precursor at high temperature and under H(2)S pressure. The best Zn(0.2)Cd(0.8)S/MoS(2) 3% showed two hundred-and-ten times (210 times) faster hydrogen generation rate on visible light illumination compared with that obtained for un-treated Zn(0.2)Cd(0.8)S. That was the most impressive catalytic enhancement ever recorded for a semiconductor photocatalyst decorated with a noble metal free electrocatalyst.

Novel cobalt/nickel–tungsten-sulfide catalysts for electrocatalytic hydrogen generation from water

The potential of water (photo)electrolysis technology to provide hydrogen as a fuel on a large scale depends on how viable electrocatalysts for the water oxidation reaction (WOR) and the hydrogen evolution reaction (HER) are and whether they can be constructed from elements which are abundant in the Earths crust. Here we show that ternary sulfides of cobalt–tungsten and nickel–tungsten (MWSx where M is Co or Ni) are efficient and robust electrocatalysts for the HER in water over a wide pH range. These novel ternary sulfides were readily grown on a conducting electrode surface by employing a scalable electrodeposition process from aqueous solutions of [M(WS4)2]2−. In terms of HER activity, the MWSx catalysts represent attractive alternatives to platinum. Moreover, we show that the HER activity is governed by the nature of the metal M within M–S–W heterobimetallic sulfide centres, located in the WS2-like layered structure of MWSx. Our work provides structural and mechanistic keys to understand how HER activity is promoted in previously described nickel and cobalt-doped molybdenum and tungsten sulfide materials.

Novel assembly of an MoS2 electrocatalyst onto a silicon nanowire array electrode to construct a photocathode composed of elements abundant on the Earth for hydrogen generation

Mild-mannered catalyst: a novel procedure to load a MoS(2) co-catalyst onto the surface of silicon under mild-conditions (room temperature, atmospheric pressure, aqueous solution) by a photo-assisted electrodeposition process employing commercially available precursors is reported. The obtained Si-NW@MoS(2) photocathode showed similar catalytic activity for light-driven H(2) generation compared with a Si-NW@Pt photocathode.

Facile Photochemical Synthesis of Graphene-Pt Nanoparticle Composite for Counter Electrode in Dye Sensitized Solar Cell

A low temperature route to synthesize graphene oxide-Pt nanoparticle hybrid composite by light assisted spontaneous coreduction of graphene oxide and chloroplatinic acid without reducing agent is demonstrated. Analysis indicates the importance of light as energy provider and ethanol as hole scavenger in the formation of small Pt nanoparticles (∼3 nm) on graphene oxide as well as graphene oxide reduction. Spray coating was used to deposit the hybrid material as a counter electrode in dye sensitized solar cells (DSCs). An efficiency of 6.77% for the hybrid graphene counter electrode has been obtained, higher than the control device made by low temperature sputtered Pt as counter electrode. Compatibility of the hybrid material with flexible plastic substrates was demonstrated yielding DSCs of an efficiency of 4.05%.

Simple route to monodispersed silica-titania core-shell photocatalysts.

A monodispersed silica-titania core-shell photocatalyst was synthesized via a sol-gel route without the need of pH adjustment, cationic polyelectrolytes, or surfactants in a process where silica spheres were impregnated with hydrolyzed titanium tetrabutoxide, incubated at room temperature, and then condensed using an ethanol/water (1:1) solvent. Four coating cycles in a 10% v/v titania sol produced homogeneous titania shells. The quality of catalysts was assessed quantitatively using Rietveld analysis of powder X-ray diffraction patterns combined with X-ray fluorescence spectrometry. During calcination, the anatase-to-rutile transformation was delayed to 1000 degrees C, which is approximately 300 degrees C higher than usually observed. The thermal stability and surface area of titania were enhanced through the slow crystal growth of anatase. The photocatalytic activity of the core-shell photocatalysts calcined at 400-600 degrees C was found to be proportional to the thickness of titania but did not directly correlate with the surface area.

Tuning the morphology of ZnMn2O4 lithium ion battery anodes by electrospinning and its effect on electrochemical performance

ZnMn2O4 structures of various morphologies (nanorods, nanofibers, nanowebs) have been prepared via a facile electrospinning technique by a simple variation of the sintering profile, and have subsequently been employed as anodes in lithium ion battery applications. After the sintering process, as-spun nanofibers with high aspect ratio have broken into short segments of ZnMn2O4 nanorods (ZMO-NR). Incorporating an intermediate carbonization step has strengthened the mechanical integrity of as-spun nanofibers, resulting in the formation of sintered nanofibers (ZMO-NF) and nanowebs (ZMO-NW). On the basis of FESEM, HRTEM and XRD studies, the formation mechanism of nanostructures consisting of hierarchically self-assembled ZnMn2O4 nanocrystals is discussed. Particle size distribution is computed by Rietveld refinement and HRTEM micrographs, while the valence states are confirmed by XPS. The initial discharge of ZMO-NF and ZMO-NW demonstrated a high capacity of ∼1469 mA h g−1 and 1526 mA h g−1, respectively, in the voltage ranges of 0.005 V and 3.0 V versus Li/Li+ at 60 mA g−1, associated with reversible capacities of ∼705 mA h g−1 and 530 mA h g−1 after 50 cycles. Morphology tuning of anodes and the importance of interconnected nanoparticulate pathways for lithium ion diffusion are elucidated.

Surfactant‐Free Sub‐2 nm Ultrathin Triangular Gold Nanoframes

Ultrathin triangular gold nanoframes are synthesized in high yield through selective gold deposition on the edges of triangular silver nanoprisms and subsequent silver etching with mild wet etchants. These ultrathin gold nanoframes are surfactant-free with tailorable ridge thickness from 1.8 to 6 nm and exhibit adjustable and distinct surface plasmon resonance bands in the visible and near-IR region. In comparison, etching of the nanoprism template by galvanic replacement can only create frame structures with much thicker ridges, which have much lower catalytic activity for 4-nitrophenol reduction than the ultrathin gold nanoframes.