Water Splitting by Tungsten Oxide Prepared by Atomic Layer Deposition and Decorated with an Oxygen-Evolving Catalyst (original) (raw)
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The Journal of Physical Chemistry C
Solar water splitting is a promising solution for the renewable production of hydrogen as an energy vector. To date, complex or patterned photoelectrodes have shown the highest water splitting efficiencies, but lack scalable routes for commercial scale-up. In this article, we report a direct and scalable chemical vapor deposition (CVD) route at atmospheric pressure, for a single step fabrication of complex nano-needle structured WO3 photoanodes. Using a systematic approach, the nanostructure was engineered to find the conditions that result in optimal water splitting. The nanostructured materials adopted a monoclinic γ-WO3 structure and were highly oriented in the (002) plane, with the nano-needle structures stacking perpendicular to the FTO substrate. The WO3 photoanode that showed the highest water splitting S2 activity was composed of a ~300 nm seed layer of flat WO3 with a ~5 µm thick top layer of WO3 nano-needles. At 1.23 VRHE, this material showed incident photon-to-current efficiencies in the range ~35-45 % in the UV region (250-375 nm) and an overall solar predicted photocurrent of 1.24 mA.cm-2 (~25 % of the theoretical maximum for WO3). When coupled in tandem with a photovoltaic device containing a methyl ammonium lead iodide perovskite, a solar-to-hydrogen efficiency of ca 1 % for a complete unassisted water splitting device is predicted.
ACS Applied Materials & Interfaces, 2013
One of the main challenges in developing highly efficient nanostructured photoelectrodes is to achieve good control over the desired morphology and good electrical conductivity. We present an efficient plasma-processing technique to form porous structures in tungsten substrates. After an optimized two-step annealling procedure, the mesoporous tungsten transforms into photoactive monoclinic WO 3. The excellent control over the feature size and good contact between the crystallites obtained with the plasma technique offers an exciting new synthesis route for nanostructured materials for use in processes such as solar water splitting.
ACS Catalysis, 2018
Further advancement in sunlight-driven splitting of water as a means of producing hydrogen and oxygen is mainly hampered by the availability of easy-to-prepare, inexpensive n-type semiconductor materials able to operate as stable and efficient photoanodes in a water photoelectrolysis cell. Here, we demonstrate that photocatalytic water oxidation currents on thin-layer semitransparent WO 3 electrodes, deposited by one-step sol-gel method on conductive oxide F-SnO 2 substrates, are dramatically improved following additional higher-temperature (ca 700°C) annealing. Largely reduced recombination of charge carriers photogenerated in activated WO 3 associated with enhanced light absorption yields at 1.23 V vs RHE, under simulated solar AM 1.5G irradiation (100 mW cm-2), water photo-oxidation currents close to 4.2 mA cm-2 on a 1.2 µm-thick photoanode-about 2 times larger than on the electrodes of the same thickness only annealed at 550°C. The relative enhancement of the photocurrent induced by the further annealing at 700°C scaled up with decreasing the film thickness with a threefold increase observed for the thinnest tested, 0.25 µm-thick WO 3 electrode that reaches 2.75 mA cm-2. We obtained such high photocatalytic water splitting performance without depositing any additional water oxidation catalyst.
Solar Energy, 2017
This paper presents a facile single step strategy for fabrication of tungsten, bismuth and vanadium mixed metal oxide nanoarrays. WO 3-BiVO 4 heteronanostructure was obtained hydrothermally with reaction time of two hrs at low temperature 110°C. The morphology of as prepared WO 3-BiVO 4 heterostructure revealed uniform and prominent nanorods like architectures under FE-SEM. These heteronanostructures were of variable sizes i.e., width 6100 nm and length 200-400 nm respectively. The energy dispersive X-ray analysis (EDX) and elemental mapping of heteronanostructure further confirmed W, Bi, V and O entities in good elemental composition. The purity and crystalline nature of as synthesized WO 3-BiVO 4 were confirmed from X-ray crystallographic (XRD) analysis. UV-Visible spectroscopy and Raman analysis were also carried out to investigate optical properties of WO 3-BiVO 4. The band gap energy of WO 3-BiVO 4 calculated from UV-Visible absorption and diffused reflectance spectroscopy's was observed to be 2.1 eV respectively. The photoelectrochemical (PEC) studies of FTO coated WO 3-BiVO 4 showed a stable and repeatable photocurrent response under 1 SUN solar irradiation source. The linear sweep voltammetry (LSV) and Cyclic Voltammetry (CV) also corroborated substantial photocurrents at different oxidation and reduction potentials. Consequently, it is envisioned that this one-step strategy for in-situ fabrication of WO 3-BiVO 4 heteronanostructures have potential applications in solar-driven photoelectrochemical water splitting reactions.
A novel photoelectrode from TiO2-WO3 nanoarrays grown on FTO for solar water splitting
Electrochimica Acta, 2014
TiO 2 -WO 3 nanorod arrays were synthesized on fluorine-doped tin oxide (FTO) substrates via a template free process, hydrothermal procedure combined with electrodeposition. The designed photoelectrodes were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and photoelectrochemical measurements. These arrays are employed as photoanodes in water splitting systems under illumination of AM 1.5 G (110 mW/cm 2 ). This study demonstrates that the WO 3 deposition interval time (0, 10, 20, 40, 60 min) can significantly affect the photoelectrochemical performance and the amount of hydrogen generated. The optimal deposition time was 20 min, which is sufficient to homogeneously coating the TiO 2 nanorods and enhance the photoconversion efficiency of TiO 2 -WO 3 array by 60% compared to pure TiO 2 array. The enhanced electrode efficiency was attributed to efficient charge separation and reduction of the electronhole pair recombination rate.
ACS Applied Materials & Interfaces, 2013
The current work demonstrates the importance of WO 3 crystallinity in governing both photoenergy conversion efficiency and storage capacity of the flower structured WO 3 electrode. The degree of crystallinity of the WO 3 electrodes was varied by altering the calcination temperature from 200 to 600°C. For the self-photochargeability phenomenon, the prevailing flexibility of the short-range order structure at low calcination temperature of 200°C favors the intercalation of the positive cations, enabling more photoexcited electrons to be stored within WO 3 framework. This leads to a larger amount of stored charges that can be discharged in an on-demand manner under the absence of irradiation for H 2 generation. The stability of the electrodes calcined at 200°C, however, is compromised because of the structural instability caused by the abundance insertion of cations. On the other hand, films that were calcined at 400°C displayed the highest stability toward both intercalation of the cations and photoelectrochemical water splitting performance. Although crystallinty of WO 3 was furthered improved at 600°C heat treatment, the worsened contact between the WO 3 platelets and the conducting substrate as induced by the significant sintering has been more detrimental toward the charge transport.
International Journal of Hydrogen Energy, 2017
Tungsten tri oxide hierarchical nanostructures (h-WO 3) and bismuth oxide (Bi 2 O 3)/h-WO 3 nanocomposite successfully prepared via a simple one-pot hydrothermal method. Structural properties of the materials reconnoitered by numerous characterization techniques such as FESEM, EDX, XRD, FT-IR and Raman. FESEM analysis designated that the h-WO 3 made of smaller layered nanorods with four axis, while the EDX analysis confirmed the elemental composition of pristine h-WO 3 and Bi 2 O 3 /h-WO 3 nanocomposite respectively. The XRD patterns revealed the formation of monoclinic crystal unit of WO 3 product. The as-prepared h-WO 3 nanostructures and Bi 2 O 3 /h-WO 3 nanocomposite displayed strong near-infrared absorption and the Raman spectrum, also indicated characteristic peaks for BieO and WeO vibrations. Based on the structural characterizations, the plausible growth mechanism for the formation of h-WO 3 nanostructures proposed. The optical properties of h-WO 3 and their nanocomposite studied through UVeVis spectrometer and decrease in bandgap observed from 2.81 eV to 2.64 eV for the later. The photoelectrochemical (PEC) study indicated that h-WO 3 is active under visible-light region and the Bi 2 O 3 incorporation further ameliorated its water splitting properties.
N,N′-Bis(2-(trimethylammonium)ethylene) perylene 3,4,9,10-tetracarboxylic acid bisimide)-(PF 6 ) 2 ] (1) was observed to spontaneously adsorb on nanocrystalline WO 3 surfaces via aggregation/hydrophobic forces. Under visible irradiation (λ > 435 nm), the excited state of 1 underwent oxidative quenching by electron injection (k inj > 10 8 s −1 ) to WO 3 , leaving a strongly positive hole (E ox ≈ 1.7 V vs SCE), which allows to drive demanding photo-oxidation reactions in photoelectrochemical cells (PECs). The casting of IrO 2 nanoparticles (NPs), acting as water oxidation catalysts (WOCs) on the sensitized electrodes, led to a 4-fold enhancement in photoanodic current, consistent with hole transfer from oxidized dye to IrO 2 occurring on the microsecond time scale. Once the interaction of the sensitizer with suitable WOCs is optimized, 1/WO 3 photoanodes may hold potentialities for the straightforward building of molecular level devices for solar fuel production.