Facile Hydrogen Evolution Reaction on WO3Nanorods

Cation Incorporation into Copper Oxide Lattice at Highly Oxidizing Potentials

Electrolyte cations can have significant effects on the kinetics and selectivity of electrocatalytic reactions. We show an atypical mechanism through which electrolyte cations can impact electrocatalyst performance─direct incorporation of the cation into the oxide electrocatalyst lattice. We investigate the transformations of copper electrodes in alkaline electrochemistry through operando X-ray absorption spectroscopy in KOH and Ba(OH)2 electrolytes. In KOH electrolytes, both the near-edge structure and extended fine-structure agree with previous studies; however, the X-ray absorption spectra vary greatly in Ba(OH)2 electrolytes. Through a combination of electronic structure modeling, near-edge simulation, and postreaction characterization, we propose that Ba2+ cations are directly incorporated into the lattice and form an ordered BaCuO2 phase at potentials more oxidizing than 200 mV vs the normal hydrogen electrode (NHE). BaCuO2 formation is followed by further oxidation to a bulk Cu3+-like BaxCuyOz phase at 900 mV vs NHE. Additionally, during reduction in Ba(OH)2 electrolyte, we find both Cu-O bonds and Cu-Ba scattering persist at potentials as low as -400 mV vs NHE. To our knowledge, this is the first evidence for direct oxidative incorporation of an electrolyte cation into the bulk lattice to form a mixed oxide electrode. The oxidative incorporation of electrolyte cations to form mixed oxides could open a new route for the in situ formation of active and selective oxidation electrocatalysts.

Designing a 3D nanoporous network via self-assembly of WO3 nanorods for improved electrocapacitive performance

This work presents the first report on effective utilization of protonated urea, to design 3D WO₃ nanoporous networks using self-assembly of WO₃ nanorods, exhibiting enhancement in electrocapacitive performance.

Improved catalytic activity of Mo1-xWxSe2 alloy nanoflowers promotes efficient hydrogen evolution reaction in both acidic and alkaline aqueous solutions

Layered transition metal dichalcogenides are noble-metal free electrocatalysts for the hydrogen evolution reaction (HER). Instead of using the common hydrothermal synthesis, which requires high pressure and temperature, herein a relatively simple and controlled colloidal synthesis was used to produce an alloy of Mo_1-xW_xSe₂ with nanoflower morphology as a model system for the electrocatalysis of hydrogen evolution in both acidic and alkaline environments. The results show that Mo_1-xW_xSe₂ alloys exhibit better catalytic activity in both acidic and alkaline solutions with low overpotentials compared to pure MoSe₂ and WSe₂. Moreover, the electrode kinetics was studied using electrochemical impedance spectroscopy (EIS) and the results indicate that the alloys exhibit improved catalytic activity with low Tafel slopes, making them appealing for HER in either environment. Additionally, when MoSe₂ nanoflowers (NFs) are prepared by using different metal salts and chalcogenide precursors, changes in the HER catalytic activity were observed, despite the morphology and crystal structure similarities. This finding suggests that different results reported in the literature could originate from different synthetic methods of the TMD, emphasizing that a better understanding of the relationship between the synthetic route and the catalytic performance is still lacking.

Fabrication of WO3 nanorods on graphene nanosheets for improved visible light-induced photocapacitive and photocatalytic performance

Visible light-induced photocatalytic degradation of organic pollutants using WO₃ nanorods–graphene nanocomposite.

Self-supported tungsten/tungsten dioxide nanowires array as an efficient electrocatalyst in the hydrogen evolution reaction

A tungsten/tungsten dioxide nanowires array was constructed on a carbon paper through the thermal annealing of tungsten trioxide, and was proven to be an efficient hydrogen evolution cathode with strong durability in acidic solutions.

In situ high temperature X-ray diffraction, transmission electron microscopy and theoretical modeling for the formation of WO3 crystallites

The structural transformation of WO₃ at high temperatures.

Efficient photoelectrochemical water oxidation over cobalt-phosphate (Co-Pi) catalyst modified BiVO4/1D-WO3 heterojunction electrodes

We report the design, synthesis and photoelectrochemical characterization of cobalt phosphate (Co-Pi) oxygen evolution catalyst modified heterojunction photoelectrodes consisting of one-dimensional WO3 nanorods (1D-WO3) and highly porous BiVO4 layers. The 1D-WO3 nanorods were prepared by the decomposition of the tetrabutylammonium decatungstate precursor in the presence of poly(ethylene glycol) as a binding agent. The porous BiVO4 layers were spray deposited using a surfactant assisted metal-organic decomposition method. The Co-Pi oxygen evolution catalyst was deposited onto the BiVO4/1D-WO3/FTO heterojunction electrode using a photoassisted electrodeposition method. The Co-Pi catalyst modified heterojunction electrodes exhibited a sustained enhancement in the photocurrent compared to the unmodified BiVO4/1D-WO3/FTO heterojunction electrodes. The improved photoelectrochemical properties profited from the enhanced charge carrier separation achieved through the integration of highly porous BiVO4 layers on top of 1D-WO3 nanorods and from the superior kinetics due to the presence of the Co-Pi oxygen evolution catalyst on top of BiVO4/1D-WO3/FTO heterojunction electrodes.

Characterization of Li-doped WO3 nanowires and their enhanced electrocatalytic oxidation of ascorbic acid

Li-doped WO₃ nanowires have been hydrothermally prepared and characterized mainly via spectroscopic methods.

Self Assembly and Properties of C:WO(3) Nano-Platelets and C:VO(2)/V(2)O(5) Triangular Capsules Produced by Laser Solution Photolysis

Laser photolysis of WCl(6) in ethanol and a specific mixture of V(2)O(5) and VCl(3) in ethanol lead to carbon modified vanadium and tungsten oxides with interesting properties. The presence of graphene's aromatic rings (from the vibrational frequency of 1,600 cm(-1)) together with C-C bonding of carbon (from the Raman shift of 1,124 cm(-1)) present unique optical, vibrational, electronic and structural properties of the intended tungsten trioxide and vanadium dioxide materials. The morphology of these samples shows nano-platelets in WO(x) samples and, in VO(x) samples, encapsulated spherical quantum dots in conjunction with fullerenes of VO(x). Conductivity studies revealed that the VO(2)/V(2)O(5) nanostructures are more sensitive to Cl than to the presence of ethanol, whereas the C:WO(3) nano-platelets are more sensitive to ethanol than atomic C.

A study of tungsten oxide nanowires self-organized on mica support

Self-organized straight nanowires of WO3 have been epitaxially grown on muscovite mica in low super-saturation conditions. Morphology, structure and chemical composition of the prepared nanostructures have been investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). SEM permits us to observe nanowire networks and substrate electron channeling patterns (ECP) simultaneously and thus to determine crystallographic direction of nanowire growth. The experimental results show that straight WO3 nanowires are orientated preferentially parallel to two of three high symmetry crystallographic directions of mica [100] and [110] or [100] and [Formula: see text]. XRD and XPS measurements indicated self-assembly of very thin nanowires of hexagonal tungsten bronze in the first stage of growth followed by the formation of stoichiometric WO3. The growth mechanism has been studied as a function of different preparation conditions with special focus on the role of potassium ions present on the mica surface. Based on obtained results a growth model of tungsten oxide nanowires on mica is proposed.

The sonochemical synthesis and characterization of Cu(1-x)Ni(x)WO4 nanoparticles/nanorods and their application in electrocatalytic hydrogen evolution

Cu(1-x)Ni(x)WO(4) (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) nanoparticles/nanorods have been prepared by a novel sonochemical method using cetyltrimethylammonium bromide (CTAB) as the structure directing agent. The prepared materials have been characterized by thermogravimetric analysis (TGA), x-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and BET specific surface area. The electrocatalytic activity towards the hydrogen evolution reaction (HER) has been studied for the Ni(2+)-substituted CuWO(4) nanoparticles by using linear sweep voltammogram measurements in a 1 M H(2)SO(4) solution. Cu(0.4)Ni(0.6)WO(4) (-473 mA cm(-2) at -1 V) shows a better catalytic activity than native CuWO(4) (-300 mA cm(-2) at -1 V).

Photodegradation of Pollutants in Air: Enhanced Properties of Nano-TiO(2) Prepared by Ultrasound

Nanocrystalline TiO(2) samples were prepared by promoting the growth of a sol-gel precursor, in the presence of water, under continuous (CW), or pulsed (PW) ultrasound. All the samples turned out to be made of both anatase and brookite polymorphs. Pulsed US treatments determine an increase in the sample surface area and a decrease of the crystallite size, that is also accompanied by a more ordered crystalline structure and the samples appear to be more regular and can be considered to contain a relatively low concentration of lattice defects. These features result in a lower recombination rate between electrons and holes and, therefore, in a good photocatalytic performance toward the degradation of NO(x) in air. The continuous mode induces, instead, the formation of surface defects (two components are present in XPS Ti 2p(3/2) region) and consequently yields the best photocatalyst. The analysis of all the characterization data seems to suggest that the relevant parameter imposing the final features of the oxides is the ultrasound total energy per volume (E(tot)/V) and not the acoustic intensity or the pulsed/continuous mode.

Optimization, Yield Studies and Morphology of WO3Nano-Wires Synthesized by Laser Pyrolysis in C2H2and O2Ambients—Validation of a New Growth Mechanism

Laser pyrolysis has been used to synthesize WO₃nanostructures. Spherical nano-particles were obtained when acetylene was used to carry the precursor droplet, whereas thin films were obtained at high flow-rates of oxygen carrier gas. In both environments WO₃nano-wires appear only after thermal annealing of the as-deposited powders and films. Samples produced under oxygen carrier gas in the laser pyrolysis system gave a higher yield of WO₃nano-wires after annealing than the samples which were run under acetylene carrier gas. Alongside the targeted nano-wires, the acetylene-ran samples showed trace amounts of multi-walled carbon nano-tubes; such carbon nano-tubes are not seen in the oxygen-processed WO₃nano-wires. The solid–vapour–solid (SVS) mechanism [B. Mwakikunga et al., J. Nanosci. Nanotechnol., 2008] was found to be the possible mechanism that explains the manner of growth of the nano-wires. This model, based on the theory from basic statistical mechanics has herein been validated by length-diameter data for the produced WO₃nano-wires.