Visible-light-promoted gas-phase water splitting using porous WO3/BiVO4 photoanodes

We recently described the use of Ti(0) microfibers as an anodization substrate for the preparation of TiO₂ nanotubes arrays as porous photoanodes. Here, we report the use of these fibers as a scaffold to build porous photoanodes based on a WO₃/BiVO₄ heterojunction. The obtained photoelectrodes show promising results under visible light irradiation for water oxidation both in a typical liquid-phase photoelectrochemical setup and in a gas phase reactor (developed in-house) based on a polymeric electrolyte membrane.     

Nanostructure-based WO3 photoanodes for photoelectrochemical water splitting

Nanostructured WO(3) has been developed as a promising water-splitting material due to its ability of capturing parts of the visible light and high stability in aqueous solutions under acidic conditions. In this review, the fabrication, photocatalytic performance and operating principles of photoelectrochemical cells (PECs) for water splitting based on WO(3) photoanodes, with an emphasis on the last decade, are discussed. The morphology, dimension, crystallinity, grain boundaries, defect and separation, transport of photogenerated charges will also be mentioned as the impact factors on photocatalytic performance.     

Efficient photoelectrochemical water splitting by anodically grown WO3 electrodes

The potentiostatic anodization of metallic tungsten has been investigated in different solvent/electrolyte compositions with the aim of improving the water oxidation ability of the tungsten oxide layer. In the NMF/H(2)O/NH(4)F solvent mixture, the anodization leads to highly efficient WO(3) photoanodes, which, combining spectral sensitivity, an electrochemically active surface, and improved charge-transfer kinetics, outperform, under simulated solar illumination, most of the reported nanocrystalline substrates produced by anodization in aqueous electrolytes and by sol-gel methods. The use of such electrodes results in high water electrolysis yields of between 70 and 90% in 1 M H(2)SO(4) under a potential bias of 1 V versus SCE and close to 100% in the presence of methanol.     

Facile synthesis of Ni-doped WO3 nanoplate arrays for effective photoelectrochemical water splitting

Journal of Solid State Electrochemistry - A two-step hydrothermal process for preparing Ni-doped WO3 nanoplate arrays (NPAs) is developed, and the obtained samples were used as a photoanode to...     

Surface characterization of WO(3)/ZrO(2) catalysts

A series of WO(3)/ZrO(2) catalysts with tungsten (W) loadings ranging from 0.5 to 11.4 wt% was prepared by incipient wetness impregnation on a preformed ZrO(2) support. The oxidic catalysts were characterized using XRD, Raman spectroscopy, XPS, ISS, and IR spectroscopy. XRD and Raman results showed that the ZrO(2) support was predominantly present in the monoclinic form. XPS and Raman measurements indicated the formation of increasing amounts of W interaction species for catalysts with W loadings up to 8.8 wt% WO(3). In addition to the W interaction species, bulk WO(3) was also observed for catalysts with W loadings > or = 3.0 wt% WO(3). Comparison of the XPS results with coverage measurements by ISS and CO adsorption suggests that the W surface phase is in the form of two-dimensional polymeric patches for catalysts with W loadings 3.0 < or = wt% WO(3) < or = 4.5. For catalysts with W loadings >4.5 wt% WO(3), the results indicated an additional build-up of a bilayer (or multilayer) polymeric W species. Analysis of the hydroxyl region of ZrO(2) by IR spectroscopy showed that initial additions of W occur on the high frequency hydroxyl group. A schematic for the structure of the catalysts has been proposed based on the above observations.     

Direct Z-scheme WO3-x nanowire-bridged TiO2 nanorod arrays for highly efficient photoelectrochemical overall water splitting

All-solid-state Z-scheme photocatalysts for overall water splitting to evolve H2 is a promising strategy for efficient conversion of solar energy.However,most o...     

Si-doped Fe2O3 nanotubular/nanoporous layers for enhanced photoelectrochemical water splitting

The present work reports the enhancement of the photoelectrochemical water splitting performance of in-situ silicon (Si)-doped nanotubular/nanoporous (NT/NP) layers. These layers were grown by self-organizing anodization on Fe-Si alloys of various Si content. The incorporation of Si is found to retard the layer growth rates, leads to a more pronounced nanotubular morphology, and most importantly, an improved photoelectrochemical behavior. By increasing Si content from 1, 2 to 5 at.% in the iron oxide NT/NP photoanodes, the photocurrent onset potential shifts favorably to lower values. At 1.3 V vs. RHE, hematite layer with 5 at.% Si shows a 5-fold increase of the photocurrent, i.e. 0.5 mA cm^− 2 in comparison to 0.1 mA cm^− 2 for the undoped samples. The study also reveals that a suitable layer thickness is essential to achieve a beneficial effect of the Si doping.     

Preparation and characterization of porous titania-grafted poly(styrene-divinylbenzene)/maleic anhydride nanocomposite microspheres

Mesoporous titania-grafted poly(styrene-divinylbenzene)/maleic anhydride [P(St-DVB)/MA] nanocomposite microspheres were prepared by an open ring reaction method.The titania nanoparticles were first modified by attachment of amino groups to their surface to prevent particle aggregation,and to allow the nanoparticles to covalently bond the polymer microspheres,the surface of which was modified by attachment of MA functional groups to enable the polymer to retain their porous structures and to react with the a...     

Two-dimensional ultrathin MoS_2-modified black Ti~(3+)-TiO_2 nanotubes for enhanced photocatalytic water splitting hydrogen production

Two-dimensional (2D) ultrathin MoS_2-modified black Ti~(3+)-TiO_2 nanotubes were fabricated using an electrospinning-hydrothermal treatment-reduction method.Bare TiO_2 nanotubes were fabricated via electrospinning.Then,2D MoS_2 lamellae were grown on the surface of the nanotubes and Ti~(3+)/Ov ions were introduced by reduction.The photocatalytic performance of the 2D MoS_2/Ti~(3+)-TiO_2 nanotubes was～15 times better than that of TiO_2.The HER enhancement of the MoS_2/Ti~(3+)-TiO_2 nanotubes can be attributed to the Pt-like behavior of 2D MoS_2 and the presence of Ti~(3+)-ions,which facilitated the quick diffusion of the photogenerated electrons to water,reducing the H_2 activation barrier.The presence of O_v ions in the nanotubes and their hollow structure increased their solar utilization.     

Synthesis of polyethylene glycol (PEG) assisted tungsten oxide (WO3) nanoparticles for L-dopa bio-sensing applications

Nanocrystalline tungsten oxides (WO_3−δ) are currently receiving a lot of attention because of their interesting electrical, magnetic, optical and mechanical properties. In this report, we present the synthesis of PEG assisted tungsten oxide (WO₃) nanoparticles by simple household microwave irradiation (2.45 GHz) method. The samples were characterized using powder X-ray diffraction (XRD), thermal analysis (TG/DTA), transmission electron microscopy (TEM), UV-visible diffusion reflectance spectroscopy (UV-VIS-DRS), cyclic voltammetry and electrochemical impedance spectroscopy. Powder XRD results revealed that both the samples prepared with and without surfactant crystallize in the orthorhombic structure corresponding to WO₃·H₂O phase. Subsequent annealing under identical conditions (600 °C/air/6 h) led to significantly different products i.e. monoclinic W₁₇O₄₇ from surfactant free sample and orthorhombic WO₃ from PEG assisted sample. Blue emission was observed through UV-VIS-DRS with blue shift and the band gap energy was estimated as 2.7 and 3.28 eV for PEG assisted as prepared (WO₃·H₂O) and annealed samples (WO₃) respectively. Electrochemical measurements have been performed on all the samples deposited on the surface of glassy carbon (GC) electrode which showed high sensitivity and good selectivity for PEG assisted sample (WO₃·H₂O) for the direct detection of l-dopa.     

Highly porous WO3/CNTs-graphite film as a novel and low-cost positive electrode for vanadium redox flow battery

Journal of Solid State Electrochemistry - In this study, novel and low-cost tungsten oxide/carbon nanotubes-graphite-polyvinyl chloride (WO3/CNTs-graphite-PVC) film with porous 3D network structure...     

A novel poly(3,4-ethylenedioxythiophene)/iron phthalocyanine/multi-wall carbon nanotubes nanocomposite with high electrocatalytic activity for nitrite oxidation

In the present work, the oxidative electrochemistry of nitrite on the poly(3,4-ethylenedioxythiophene)/iron phthalocyanine/multi-wall carbon nanotubes-(PEDOT/FePc/MWCNT) modified screen-printed carbon electrodes (SPCE) has been investigated. The parameters, such as overpotential, current density and rate constant at PEDOT/FePc/MWCNT-modified SPCE, were compared with an un-modified, FePc-, and FePc/MWCNT-modified SPCE for electro-oxidation of nitrite. As compared with the un-modified SPCE, an increase in the anodic peak current density (J_pa) (∼100%) along with a decrease in the anodic peak potential (E_pa) of ∼150 mV for electro-oxidation of nitrite at the FePc-modified SPCE was observed. When an under-layer of MWCNT was introduced onto FePc-modified SPCE, denoted as FePc/MWCNT-modified SPCE, and the number of FePc/MWCNT bilayer was optimized, the heterogeneous electron transfer rate constant (k) at FePc/MWCNT-modified SPCE was enhanced about 7.8 times as compared with that at FePc-modified SPCE. Moreover, as a layer of PEDOT film was electrodeposited onto the FePc/MWCNT-modified SPCE, denoted as PEDOT/FePc/MWCNT-modified SPCE, a significant increase in current response along with a remarkable decrease in E_pa were noticed. This can be attributed to the pre-concentration effect induced by the electrostatic interaction between the negatively charged nitrite and oxidized PEDOT film. On the whole, the PEDOT/FePc/MWCNT-modified SPCE greatly reduces the overpotential of ∼330 mV along with 3.5 times enhanced the peak current density for the electro-oxidation of nitrite as compared with un-modified SPCE. The sensitivity and limit of detection (S/N = 3) for the PEDOT/FePc/MWCNT-modified SPCE were found to be as 638 mA cm⁻² M⁻¹ and 71 nM, respectively. Notably, PEDOT/FePc/MWCNT-modified SPCE has a lower sensing potential than compared to several other modified electrodes. The developed sensor was also applied for the determination of nitrite in tap water sample.     

Photocrosslinked methacrylated poly(vinyl alcohol)/hydroxyapatite nanocomposite hydrogels with enhanced mechanical strength and cell adhesion

Poly(vinyl alcohol) (PVA) hydrogels with high water content, good load‐bearing property, low frictional behavior as well as excellent biocompatibility have been considered as promising cartilage replacement materials. However, the lack of sufficient mechanical properties and cell adhesion are two critical barriers for their application as cartilage substitutes. To address these problems, herein, methacrylated PVA with low degree of substitution of methacryloyl group has been synthesized first. Then, methacrylated PVA‐glycidyl methacrylate/hydroxyapatite (PVA‐GMA/Hap) nanocomposite hydrogels have been developed by the photopolymerization approach subsequently. Markedly, both pure PVA‐GMA hydrogel and PVA‐GMA/Hap nanocomposite hydrogels exhibit excellent performance in compressive tests, and they are undamaged during compressive stress–strain tests. Moreover, compared to pure PVA‐GMA hydrogels, 8.5‐fold, 7.4‐fold, and 14.2‐fold increase in fracture stress, Young's modulus and toughness, respectively, can be obtained for PVA‐GMA/Hap nanocomposite hydrogels with 10 wt % Hap nanoparticles. These enhancements can be ascribed to the intrinsic property of PVA‐GMA and strong hydrogen bonding interactions between PVA‐GMA chain and Hap nanoparticles. More interestingly, significant improvement in the cell adhesion can also be successfully achieved by incorporation of Hap nanoparticles. These biocompatible nanocomposite hydrogels have great potential to be used as cartilage substitutes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1882–1889     

Kappa carrageenan-g-poly (acrylic acid)/SPION nanocomposite as a novel stimuli-sensitive drug delivery system

In this article, a novel triple-stimuli hydrogel was prepared by simultaneous formation of super paramagnetic iron oxide nanoparticles (SPION) and crosslinking of poly (acrylic acid) grafted onto kappa carrageenan (κC-g-PAA). The structure, thermal stability, surface morphology, and magnetic property of the κC-g-PAA/SPION hydrogel were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy with energy dispersive X-ray analysis (SEM–EDAX), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM). Moreover, swelling capacity of the obtained hydrogel was measured at different temperature, pH, and magnetic-field to assess the sensitivity of κC-g-PAA/SPION hydrogel. This synthetic hydrogel was also examined as a controlled drug delivery system and defrasirox release was investigated at different temperature, pH, and magnetic-field. The in vitro antibacterial activity of κC-g-PAA/SPION hydrogel was studied against Escherichia coli and Staphylococcus aureus bacteria where the results showed no antibacterial activity of this new hydrogel. In vitro biocompatibility experiments were undertaken using human bladder epithelial cell line HTB 5637. These results indicated the synthesized κC-g-PAA/SPION hydrogel are nontoxic that will be useful for biomedical applications.

WO3 homojunction photoanode: Integrating the advantages of WO3 different facets for efficient water oxidation

The manipulation of the surface property of WO₃ photoanode is the main breakthrough direction to improve its solar water oxidation performance both in thermodynamics and kinetics.Here,we report a WO₃(002)/m-WO₃ homojunction film that is composed of an upper WO₃ layer with predominant(002)facet(WO₃(002))and a lower WO₃ layer with multi-crystal facets(m-WO₃)as a photoanode for solar water oxidation.Due to the synergistic effect of WO₃(002)layer and m-WO₃ layer,better water oxidation activity and stability are achieved on the WO₃(002)/m-WO₃ homojunction film relative to the m-WO₃ and WO₃(002)film.Specifically,the improved water oxidation performance on the WO₃(002)/m-WO₃ homojunction film is attributed to the followings.In thermodynamics,the band position differences between WO₃(002)layer and m-WO₃ layer lead to the formation of WO₃(002)/m-WO₃ homojunction,which has positive function of improving their charge separation and transfer.In kinetics,the upper WO₃(002)layer of the WO₃(002)/m-WO₃ film has superior activity in the adsorption and activation of water molecules,water oxidation on this homojunction film photoanode is inclined to follow the four-holes pathway,and the corrosion of photoanode from the H₂O₂ intermediate is restrained.The present work provides a new strategy to modify the WO₃ photoanodes for thermodynamically and kinetically efficient water oxidation.     

Poypyrrole/molybdenum trioxide/graphene nanoribbon ternary nanocomposite with enhanced capacitive performance as an electrode for supercapacitor

A polypyrrole/molybdenum trioxide/graphene nanoribbon (PPy/MoO₃/GNR) ternary nanocomposite was successfully synthesized via an in situ method. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses show that MoO₃ was successfully combined with the GNRs. The one-dimensional morphology was observed using field emission scanning electron microscopy and transmission electron microscopy. The electrochemical tests show that the PPy/MoO₃/GNR ternary nanocomposite exhibits the highest specific capacitance (844 F g^?1) among the investigated materials and exhibits good cycling stability for 1000 cycles. These results collectively demonstrate that the combination of each component can efficiently increase the specific capacitance and cycling stability. As such, the method reported herein represents a promising approach for fabricating supercapacitor electrode materials.     

Amorphous porous sulfides nanosheets with hydrophilic/aerophobic surface for high-current-density water splitting

The rational construction of electrocatalysts with desired features is significant but challenging for superior water splitting at high current density. Herein, amorphous CoNiS nanosheets are synthesized on nickel foam (NF) through a facile structure evolution strategy and present advanced performance at high current densities in water splitting. The high catalytic activity can be attributed to the sufficient active sites exposed by the flexible amorphous configuration. Moreover, the hydrophilicity and aerophobicity of a-CoNiS/NF promote surface wettability of the self-supporting electrode and avoid the aggregation of bubbles, which expedites the diffusion of electrolyte and facilitates the mass transfer. As a result, the optimized electrode demonstrates low overpotentials of 289 and 434 mV at 500 mA/cm² under alkaline conditions for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Impressively, an electrolytic water splitting cell assembled by bifunctional a-CoNiS/NF operates with a low cell voltage of 1.46 V@10 mA/cm² and reaches 1.79 V at 500 mA/cm². The strategy sheds light on a competitive platform for the reasonable design of non-precious-metal electrocatalysts under high current density.     

Tungsten doping of Ta3N5-nanotubes for band gap narrowing and enhanced photoelectrochemical water splitting efficiency

Ordered W-doped Ta₂O₅ nanotube arrays were grown by self-organizing electrochemical anodization of TaW alloys with different tungsten concentrations and by a suitable high temperature ammonia treatment, fully converted to W:Ta₃N₅ tubular structures. A main effect found is that W doping can decrease the band gap from 2 eV (bare Ta₃N₅) down to 1.75 eV. Ta₃N₅ nanotubes grown on 0.5 at.% W alloy and modified with Co(OH)_x as co-catalyst show ~ 33% higher photocurrents in photoelectrochemical (PEC) water splitting than pure Ta₃N₅.     

Synthesis and characterization of novel segmented polyurethane/clay nanocomposite via poly(ε-caprolactone)/clay

A novel segmented polyurethane/clay (PU/clay) nanocomposite based on poly(caprolactone), diphenylmethane diisocyanate, butanediol, and poly(caprolactone)/clay prepolymer was synthesized as evidenced by FTIR and X-ray diffraction studies. Poly(caprolactone)/clay (PCL/clay) prepolymer was first synthesized in a nanocomposite form as confirmed by X-ray diffraction. X-ray diffraction study showed that PU/clay contained crystalline structure due to the presence of PCL/clay. In mechanical properties, about 1.4% PCL/clay in PU/clay resulted in a large increase in the elongation of PU/clay. However, when the amount of PCL/clay was 4.2%, the elongation of PU/clay was reduced drastically. This behavior indicated that PU/clay can be transformed from an elastomer to a thermoplastic material as the amount of PCL/clay in PU/clay increased. Additionally, the lap shear stress of PU/clay was at least three times that of neat PU as a result of the PCL/clay component. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2225–2233, 1999     

A novel route for the synthesis of nanocomposite tungsten carbide–cobalt using a biopolymer as a carbon source

A new synthetic route to nanoparticulate tungsten carbide–cobalt is demonstrated, using a sol–gel approach in an aqueous solution containing a biopolymer. On calcination, the biopolymer was found to act both as a source of carbon and also as an anti-sintering, structure-directing template. By keeping the tungsten carbide phase nanoparticulate, the hardness was found to be commensurate with that seen in more traditional ‘heat and beat’ syntheses. This research was supported by the Royal Society through their University Research Fellowship scheme.