WO3 Nanoplate Arrays Research Articles

Efficient WO3 Nanoplate Arrays Photoanode Modified by ZnO Nanosheets for Enhanced Charge Separation and Transfer to Promote Photoelectrochemical Performances

AbstractA key factor in the photoelectrochemical (PEC) performance of photoelectrodes is the efficient separation and transfer of photogenerated charges. Herein, a novel photoanode comprising three‐dimensional (3D) WO3 nanoplate@ZnO nanosheet hierarchical type‐II heterojunction arrays (3D WO3@ZnO HHAs) is designed and constructed via modification of the WO3 nanoplate arrays with ZnO nanosheets. The synthesized materials are characterized viaX‐ray diffraction (XRD), ultraviolet and visible spectrophotometry (UV–vis), scanning electon microscopy (SEM), transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS) analyses. Photoelectrochemical (PEC) test results reveal that the synthesized 3D WO3@ZnO HHAs photoanode exhibits reduced charge transfer resistance, improved electron‐hole pair life, and enhanced photocurrent density (≈4.5 times increase in comparison to that of the bare WO3). The increased light capture and high surface area in contact with the electrolyte as well as the enhanced charge transfer through the synergy between morphology and band structures may be responsible for the improved PEC characteristics.

Highly-efficient uranium reduction, organic oxidation and electricity generation via a solar-driven wastewater resourceization system with a PANI/CF cathode

Co-existed organics bring great challenges for uranium recycling from water because of the formation of obstinate complexes with uranyl ions (UO22+), predominated species of uranium in water). Here, we proposed an effective strategy to simultaneously decompose organics and recycle uranium from complex radioactive wastewater, combined with electricity production, by a solar-driven wastewater resourcization system (SWRS), in which an electrodeposited polyaniline (PANI) decorated carbon fiber (CF-PANI) cathode was used for highly efficient UO22+ reduction based on the abundant –NH- groups and conductivity of PANI. Under sunlight illumination, a BiVO4 decorated WO3 nanoplate array (BVO/WNP) combined with a rear silicon cell (SC) was applied as the monolithic photoanode to generate oxidative holes and derived hydroxyl radicals for robust organic oxidation, and driven electrons to the CF-PANI cathode for uranium reduction and simultaneous electricity generation at external circuit. Compared to CF, the optimized CF-PANI improved the rate constants (k) by 6 and 6.7 times for UO22+ and organic removal, respectively, and enhanced power output by 2 times (Pmax, 1.12 mW/cm2). Additionally, near 100 % removal ratios for both UO22+ and organics accompanying with Pmax around 1 mW/cm2 were achieved by SWRS when treating model complex wastewater under wide conditions or even under real sunlight illumination. The fixed uranium on the CF-PANI cathode was mainly reduced into U(IV) species (95.8 %) and the repeated tests demonstrated the excellent stability of SWRS (without obvious decay after reusing 15 times). This work provides new insights on the resourceful treatment of radioactive wastewater and contaminated waters.

Highly active and stable CuAlOx/WO3 photoanode for simultaneous pollutant degradation, hydrogen and electricity generation

An unassisted solar water-energy nexus system (SWENS) based on an ultra-thin CuAlOx overlayer coated WO3 nanoplate array (CuAlOx/WO3) photoanode, a rear silicon solar cell and a Pt-black/Pt cathode was proposed to efficiently degrade refractory organic pollutants and simultaneously produce hydrogen and electricity. The formed p-n junction between p-type CuAlOx and n-type WO3 effectively facilitated the charge separation in the CuAlOx/WO3 photoanode. Moreover, the CuAlOx overlayer enhanced the capture of photogenerated holes and isolated WO3 from the solution, thereby improving the charge transfer and inhibiting the photocorrosion of WO3. Therefore, the optimized CuAlOx/WO3 photoanode showed a significantly enhanced and stable photocurrent density of ∼2.82 mA cm−2 at 1.0 V vs. Ag/AgCl, which was ∼4 times higher than that of the pristine WO3. Based on this outstanding photoelectrocatalytic performance, the assembled SWENS showed a degradation efficiency of nearly 100% for tetracycline, a hydrogen generation rate of ∼26.8 μmol·h−1·cm−2 and a power density of ∼593 μW cm−2 under simulated solar light illumination. Our SWENS also exhibited outstanding universality in degrading various refractory organic pollutants for green energy production.

Fast electrochromic response and high coloration efficiency of Al-doped WO3 thin films for smart window applications

Herein, vertically aligned Al:WO3 nanoplate arrays were directly grown on ITO glass by a facile electrodeposition method and annealed in an argon atmosphere at 450 °C for 2h. Besides, this study reports the influence of Al doping on the electrochromic properties of WO3 film in detail. Electrochromic properties such as cyclic voltammetry, chronoamperometry and optical transmittance were analyzed by protonic insertion/extraction in the 1 M LiClO4/propylene carbonate as an electrolyte. The noticeable reversible color changing from transparent to the blue can be realized under the potential bias of ±1.0 V. XRD studies show that the produces films have highly crystalline structure. The EDS results clearly confirm the incorporation of Al element into the WO3 network. From the optical absorption measurement, direct band gap energies are calculated as 3.62 and 3.34 eV for the WO3 and the Al:WO3, respectively. Compared to the as-prepared WO3, the Al:WO3 film exhibits outstanding electrochromic performance, including wide optical modulation (55.9%), high coloration efficiency (148.1 cm2C-1), quick reaction kinetics (1.23 s and 1.01 s for colored and bleaching times, respectively), good rate capability and cycle durability at a wavelength of 632.8 nm. EIS measurements based on a charge-transfer resistance reveal that the dramatic improvement in the electrochemically active surface is achieved in the Al:WO3 film. The increase of active surface facilitates transport kinetics for electron and ion intercalation/deintercalation within the porous metal oxide to enhance coloration efficiency. Comparatively energy levels of the WO3 and the Al:WO3 electrochromic films are also represented. From the Mott-Schottky studies, it is estimated that the donor concentration of the films is of the order of 1020 cm−3. Taken together, these results not only provide important insight into a promising electrode for electrochromic displays applications, but also offer an economic and effective strategy for manufacturing of other doped metal oxide films.

Surface oxygen vacancies on WO3 nanoplate arrays induced by Ar plasma treatment for efficient photoelectrochemical water oxidation

The construction of surface defects on semiconductor oxide photoanodes has been identified as a promising route for attaining improved photoelectrochemical (PEC) performance. Here, Ar plasma treatment has been used to etch the surface of hydrothermally synthesized WO3 nanoplate array films, which generated surface oxygen vacancies (Ovs) with the concomitant reduction of surface W6+ to W5+/W4+. As a result, the visible-light absorption and photogenerated charge separation of WO3 was enhanced, as evidenced by X-ray photoelectron spectroscopy (XPS), UV/Vis diffuse-reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. A WO3 photoanode subjected to Ar plasma treatment for 120 s exhibited a photocurrent density of 1.32 mA cm−2 and an O2 evolution rate of 1.0 μmol cm−2·min−1 under simulated solar light irradiation at a bias potential of 1.23 V vs. reversible hydrogen electrode, approximately 1.7- and 5-times higher, respectively, than those of a pristine sample. This improvement is mainly attributed to the facilitative effect of surface oxygen vacancy defects, which promote electron–hole generation and separation rates and decrease the interfacial charge-transfer resistance between the WO3 photoanode and electrolyte. Our Ar plasma surface modification also has potential for developing other photoanodes for efficient PEC performance.

Jet Nebulizer Sprayed WO3-Nanoplate Arrays for High-Photoresponsivity Based Metal–Insulator–Semiconductor Structured Schottky Barrier Diodes

Monoclinic WO3-nanoplate arrays have been effectively deposited via simple jet nebulizer spray pyrolysis technique at an optimized substrate temperature of 400 °C. These WO3-nanoplate arrays were used as an insulating layer in the metal–insulator–semiconductor (MIS) structure based Schottky barrier diodes. The effect of WO3 mol concentration during the deposition process was systematically interpreted with respect to the structural, morphological, optical and electrical properties of WO3-nanoplate array films. XRD pattern exposed the polycrystalline nature of the prepared films with a monoclinic phase. At higher concentration of 0.25 M WO3-nanoplates were firmly interconnected together and has been analyzed by a FE-SEM. From UV–Vis spectroscopy, the band gap values of the WO3 were found to vary from 3.2 to 3.4 eV with mole concentrations. DC electrical study recorded a steep increase in the electrical conductivity for the film prepared with 0.2 M of WO3. Notably, all the diodes exhibited positive photoresponse under illumination. Particularly, the MIS diode fabricated with 0.2 M revealed higher photoresponsivity and sensitivity of 960.85% and 33.40 mA W−1 respectively.

WO3/BiVO4 Type-II Heterojunction Arrays Decorated with Oxygen-Deficient ZnO Passivation Layer: A Highly Efficient and Stable Photoanode

In the present work, we report a ternary WO3/BiVO4/ZnO photoanode with boosted PEC efficiency and stability toward highly efficient water splitting. The type-II WO3/BiVO4 heterojunction arrays are firstly prepared by hydrothermal growth of WO3 nanoplate arrays onto the substrates of fluorine-doped tin oxide (FTO)-coated glass, followed by spin-coating of BiVO4 layers onto the WO3 nanoplate surfaces. After that, thin ZnO layers are further introduced onto the WO3/BiVO4 heterojunction arrays via atomic layer deposition (ALD), leading to the construction of ternary WO3/BiVO4/ZnO photoanodes. It is verified that the ZnO thin layer in the WO3/BiVO4/ZnO photoanode contains abundant oxygen vacancies, which could act as an effective passivation layer to enhance the charge separation and surface water oxidation kinetics of photogenerated carriers. The as-prepared WO3/BiVO4/ZnO photoanode produces a photocurrent of 2.96 mA cm-2 under simulated sunlight with an incident photon-to-current conversion efficiency (IPCE) of ∼72.8% at 380 nm at a potential of 1.23 V versus RHE without cocatalysts, both of which are comparable to the state-of-the-art WO3/BiVO4 counterparts. Moreover, the photocurrent of the WO3/BiVO4/ZnO photoanode shows only 9% decay after 6 h, suggesting its high photoelectrochemical (PEC) stability.

Conformal BiVO4-Layer/WO3-Nanoplate-Array Heterojunction Photoanode Modified with Cobalt Phosphate Cocatalyst for Significantly Enhanced Photoelectrochemical Performances

Constructing semiconductor heterojunctions via surface/interface engineering is an effective way to enhance the charge carrier separation/transport ability and thus the photoelectrochemical (PEC) properties of a photoelectrode. Herein, we report a conformal BiVO4-layer/WO3-nanoplate-array heterojunction photoanode modified with cobalt phosphate (Co-Pi) as oxygen evolution cocatalyst (OEC) for significant enhancement in PEC performances. The BiVO4/WO3 nanocomposite is fabricated by coating a thin conformal BiVO4 layer on the surface of presynthesized WO3 nanoplate arrays (NPAs) via stepwise spin-coating, and the decoration of Co-Pi OEC is realized by photoassisted electrodeposition method. The optimized Co-Pi@BiVO4/WO3 heterojunction photoanode shows a maximum photocurrent of 1.8 mA/cm2 at 1.23 V vs RHE in a phosphate buffer electrolyte under an AM1.5G solar simulator, which is 5 and 12 times higher than those of bare WO3 and BiVO4 photoanode, respectively. Measurements of UV-vis absorption spectra, electrochemical impedance spectra (EIS) and photoluminescence (PL) spectra reveal that the enhanced PEC performances can be attributed to the increased charge carrier separation/transport benefited from the type II nature of BiVO4/WO3 heterojunction and the promoted water oxidation kinetics and photostability owing to the decoration of Co-Pi cocatalyst.

Total organic carbon and total nitrogen removal and simultaneous electricity generation for nitrogen-containing wastewater based on the catalytic reactions of hydroxyl and chlorine radicals

The treatment of nitrogen-containing organic wastewater is a difficult problem because organic and nitrogen contents are hard to remove simultaneously for the common sewage disposal technologies. Here we propose a new method to efficiently remove total organic carbon and total nitrogen and generate electricity simultaneously for this wastewater. The key idea of design is that organics and ammonia nitrogen is converted into CO2 and N2 by catalytic reacting with hydroxyl and chlorine radicals, respectively, while generating electricity concurrently in a self-biased wastewater fuel cell. Nitrate-N (including original or generated) was reduced on Pd/Cu modified Ni foam electrode with high selectivity toward N2, realizing the completely removal of total nitrogen from the water. Moreover, self-bias voltage was generated by employing WO3 nanoplate array electrodes and silicon photovoltaic cells as a hybrid photoanode to enhance the charge separation. This system was also successful in extending the light harvest. A series of experiments were performed with nitrate-N (ammonium-N) and phenol and the results indicated the removal efficiency of nitrate-N (ammonium-N) was 98.7% (91.5%) in 90 min and total nitrogen was efficiently transformed to N2 with extending time to 120 min. The system also showed a superior performance for phenol degradation (99.1% in 90 min). Combined with the analysis of ESR and free radical capture experiment, it was concluded that chlorine radical played an important role in the phenol and ammonia-N oxidation. In addition, maximum power density output of the system reached 1.23 mW cm−2. This study offers a self-sustaining approach for simultaneous nitrogen-containing organic wastewater treatment and electricity production.

A self-sustaining monolithic photoelectrocatalytic/photovoltaic system based on a WO3/BiVO4 photoanode and Si PVC for efficiently producing clean energy from refractory organics degradation

A novel self-sustaining monolithic photoelectrocatalytic/photovoltaic (SMPP) system is constructed with a FTO-glass-based WO3/BiVO4 photoanode, which was prepared by coating BiVO4on WO3 nanoplate array using simple wet chemical methods, a rear Si photovoltaic cell (PVC) and a counter Pt-black/Pt cathode. The optimum SMPP system shows an efficient and stable degradation of tetracycline hydrochloride with a rate constant 0.75 h−1, and yields an open circuit voltage 1.35 V, a short circuit current 2900 μA cm−2, a power density 1112 μW cm−2, which is nearly 14 times that of theultimate conventional photocatalytic fuel cell to date, and a hydrogen generation rate 52.6 μmol h−1 cm−2. This outstanding performance should be due to the efficient electron/hole separation and light exploitation, because, under stimulated sunlight illumination, the front WO3/BiVO4 photoanode absorbs short-wavelength photons and generates electron/hole pairs, in which the photogenerated holes can oxidize organics, while the rear Si PVC captures the transmitting longer-wavelength photons to generate photovoltage that drives photogenerated electrons to the cathode for reducing H+ to H2 and generating electricity in the external-circuit. The results also demonstrate that various refractory organics can be efficiently decomposed along with the production of electricity and hydrogen by the SMPP system. This work provides a more efficient way to dispose organics and simultaneously produce clean energy than conventional technologies and serves well as a promising technology for wastewater recycling.

Bipyridine-Co2+ molecular catalyst modified WO3 nanoplate arrays photoanode with enhanced photoelectrochemical activity

Here we report for the first time that bpy-Co2+ complex (bpy = 4,4′-bipyridine) can be used as an efficient molecular co-catalyst to significantly enhance photoelectrochemical (PEC) activity of WO3 nanoplate arrays photoanode. As a result, bpy-Co2+ complex modified WO3 nanoplate arrays photoanode achieved a considerable photocurrent density (2.88 mA cm−2) at 1.5 V versus a reversible hydrogen electrode (RHE), which is 1.7 and 1.4-times larger than that obtained by WO3 photoanode without any modification (1.61 mA cm−2) and cobalt phosphate (Co-Pi) modified WO3 photoanode (2.01 mA cm−2) in Na2SO4 electrolyte, respectively. The present work provides a new strategy for designing highly efficient PEC water splitting device.

Improving Visible-light Responses and Electric Conductivities by Incorporating Sb2S3 and Reduced Graphene Oxide in a WO3 Nanoplate Array for Photoelectrochemical Water Oxidation

The WO3, reduced graphene oxide (rGO), and Sb2S3 nanocomposite is firstly synthesized on a transparent conducting oxide glass by using a chemical bath deposition method coupled with a post-thermal treatment for catalysing the artificial photosynthesis under the framework of Z–scheme water splitting. Sb2S3 acts as the light absorber to mitigate poor visible light absorption and rGO serves as a electrically conductive layer to enhance the low quantum efficiency of WO3. An improved photocurrent density of 1.20mA/cm2 (at 1.23V vs. RHE) is obtained for the WO3/rGO/Sb2S3 electrode under AM 1.5G illumination, comparing to those for the WO3/Sb2S3 (0.27mA/cm2) and WO3 (0.05mA/cm2) electrodes. The negatively shifted onset potential of 0.35V vs. RHE is obtained when Sb2S3 and rGO are participated in the WO3 electrode, as compared with those of 0.42 and 0.45V vs. RHE for the WO3/Sb2S3 and WO3 electrodes, respectively. The improvements on the photoelectrochemical performances for the WO3/rGO/Sb2S3 electrode is primarily due to the broader light absorption and the enhanced electric conductivity. The results suggest that an efficient photocatalyst for water oxidation can be fabricated by carefully designing the composition of the nanocomposite with complementary optical and electrical preperties.

Highly selective transformation of ammonia nitrogen to N2 based on a novel solar-driven photoelectrocatalytic-chlorine radical reactions system

A highly selective method for transforming ammonia nitrogen to N2 was proposed, based on a novel solar-driven photoelectrocatalytic-chlorine radical reactions (PEC-chlorine) system. The PEC-chlorine system was facilitated by a visible light response WO3 nanoplate array (NPA) electrode in an ammonia solution containing chloride ions (Cl−). Under illumination, photoholes from WO3 promote the oxidation of Cl− to chlorine radical (Cl). This radical can selectively transform ammonia nitrogen to N2 (79.9%) and NO3− (19.2%), similar to the breakpoint chlorination reaction. The ammonia nitrogen removal efficiency increased from 10.6% (PEC without Cl−) to 99.9% with the PEC-chlorine system within 90 min operation, which can be attributed to the cyclic reactions between Cl−/Cl and the reaction intermediates (NH2, NHCl, etc.) that expand the degradation reactions from the surface of the electrodes to the whole solution system. Moreover, Cl is the main radical species contributing to the transformation of ammonia nitrogen to N2, which is confirmed by the tBuOH capture experiment. Compared to conventional breakpoint chlorination, the PEC-chlorine system is a more economical and efficient means for ammonia nitrogen degradation because of the fast removal rate, no additional chlorine cost, and its use of clean energy (since it is solar-driven).

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

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 produce a highly active and stable electrocatalyst for photoelectrochemical (PEC) water splitting under visible light. The NPAs are formed as a single-phase solid solution with high purity. X-ray photoelectron spectroscopy measurement verifies the binding energy of W element is negatively shifted due to the substitution of W6+ by Ni2+ in the monoclinic lattice and thereby the formation of Ni-O-W bonds. Notably, the two-step 3 at% Ni-doped WO3 NPAs exhibits the highest PEC performance, compared with pure and one-step Ni-doped WO3 NPAs. At 1.0 V (vs Ag/AgCl), the current density of two-step 3 at% Ni-doped WO3 is 0.80 mA/cm2, which is about 1.74- and 2.35-fold of that of WO3 (0.46 mA/cm2) and one-step 3 at% Ni-doped WO3 (0.34 mA/cm2), respectively. The PEC performance of WO3 NPAs can be modified by Ni doping in a two-step hydrothermal process; both the changes of band gap and electrochemically active surface area (ECSA) are playing important roles on improving the activity of the WO3 NPAs photoanode.

Facile morphology control of WO3 nanostructure arrays with enhanced photoelectrochemical performance

A moderate hydrothermal approach has been developed to synthesize the perpendicular oriented WO3 nanostructure films. The morphology of the WO3 films could be easily controlled by adjusting the applied amount of HCl in the synthesis procedure. The effects of acidic conditions on morphological control were investigated in details, and the formation process of WO3 nanostructures varying from nanoplates to nanorods has been proposed. Both typical platelike and rodlike nanostructure arrays demonstrate better photoelectrochemical performance than other WO3 nanostructures. The WO3 nanoplate arrays showed a superior photocurrent density of about 1.0mA/cm2 at 1.6V vs. RHE, compared to 0.8mA/cm2 of the WO3 nanorod arrays. The increased photocurrent can be mainly attributed to the larger active surface area and more effective charge transfer. Approximately 55% improvement in photoelectrochemical catalytic efficiency was obtained by the WO3 nanoplates photoanode in comparison to the nanorods photoanode in a methyl orange degradation experiment. Such results demonstrate the importance of morphology optimization for improving the photoelectrochemical performance. And the method provides a facile and reasonable way for nanostructure design and morphology control of the photoelectrodes in photoelectrochemical devices.

Preparation of vertically aligned WO3 nanoplate array films based on peroxotungstate reduction reaction and their excellent photoelectrocatalytic performance

Here, we developed a novel, facile, controllable and scalable method based on peroxotungstate reduction reaction to prepare vertically aligned WO3 nanoplate array (NPA) films with preferentially exposed highly reactive (002) facets used in efficient photoelectrocatalytic (PEC) applications. In this method, a slow and controllable reduction of peroxotungstates by ethanol was used, which was the critical step to ensure the uniform and ordered synthesis of orthorhombic WO3H2O NPA films which assembled directly on F-doped tin oxide substrates under the capping effect of oxalate, and subsequently WO3H2O NPA films were converted into monoclinic WO3 NPA films by calcination. The effects of synthetic temperature and time, and the concentration of oxalate on the crystalline phase and morphology of the WO3H2O films were studied systematically. The WO3 NPA film annealed at an optimized temperature of 500°C exhibited the highest water splitting current density of ∼1.42mA/cm2 at 1.23V vs RHE in 0.1M Na2SO4 under AM 1.5G illumination. It was further improved by decorating with a Co–Pi co-catalyst, which achieved a more stable current density of ∼1.95mA/cm2 with an incident photon-to-current conversion efficiency of ∼51% at 400nm. The WO3 NPA film also showed excellent stability and efficiency (rate constant ∼0.8127h−1) for PEC degradation of methylene blue.

Facile Fabrication of Sandwich Structured WO3 Nanoplate Arrays for Efficient Photoelectrochemical Water Splitting.

Herein, sandwich structured tungsten trioxide (WO3) nanoplate arrays were first synthesized for photoelectrochemical (PEC) water splitting via a facile hydrothermal method followed by an annealing treatment. It was demonstrated that the annealing temperature played an important role in determining the morphology and crystal phase of the WO3 film. Only when the hydrothermally prepared precursor was annealed at 500 °C could the sandwich structured WO3 nanoplates be achieved, probably due to the crystalline phase transition and increased thermal stress during the annealing process. The sandwich structured WO3 photoanode exhibited a photocurrent density of 1.88 mA cm(-2) and an incident photon-to-current conversion efficiency (IPCE) as high as 65% at 400 nm in neutral Na2SO4 solution under AM 1.5G illumination. To our knowledge, this value is one of the best PEC performances for WO3 photoanodes. Meanwhile, simultaneous hydrogen and oxygen evolution was demonstrated for the PEC water splitting. It was concluded that the high PEC performance should be attributed to the large electrochemically active surface area and active monoclinic phase. The present study can provide guidance to develop highly efficient nanostructured photoelectrodes with the favorable morphology.

Synergistic crystal facet engineering and structural control of WO3 films exhibiting unprecedented photoelectrochemical performance

WO3 nanoplate arrays with (002) oriented facets grown on fluorine doped SnO2 (FTO) glass substrates are tailored by tuning the precursor solution via a facile hydrothermal method. A 2-step hydrothermal method leads to the preferential growth of WO3 film with enriched (002) facets, which exhibits extraordinary photoelectrochemical (PEC) performance with a remarkable photocurrent density of 3.7mAcm–2 at 1.23V vs. revisable hydrogen electrode (RHE) under AM 1.5G illumination without the use of any cocatalyst, corresponding to ~93% of the theoretical photocurrent of WO3. Density functional theory (DFT) calculations together with experimental studies reveal that the enhanced photocatalytic activity and better photo-stability of the WO3 films are attributed to the synergistic effect of highly reactive (002) facet and nanoplate structure which facilitates the photo–induced charge carrier separation and suppresses the formation of peroxo-species. Without the use of oxygen evolution cocatalysts, the excellent PEC performance, demonstrated in this work, by simply tuning crystal facets and nanostructure of pristine WO3 films may open up new opportunities in designing high performance photoanodes for PEC water splitting.

In situ synthesis of Bi2S3 sensitized WO3 nanoplate arrays with less interfacial defects and enhanced photoelectrochemical performance.

In this study, Bi2S3 sensitive layer has been grown on the surface of WO3 nanoplate arrays via an in situ approach. The characterization of samples were carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and ultraviolet–visible absorption spectroscopy (UV-vis). The results show that the Bi2S3 layer is uniformly formed on the surface of WO3 nanoplates and less interfacial defects were observed in the interface between the Bi2S3 and WO3. More importantly, the Bi2S3/WO3 films as photoanodes for photoelectrochemical (PEC) cells display the enhanced PEC performance compared with the Bi2S3/WO3 films prepared by a sequential ionic layer adsorption reaction (SILAR) method. In order to understand the reason for the enhanced PEC properties, the electron transport properties of the photoelectrodes were studied by using the transient photocurrent spectroscopy and intensity modulated photocurrent spectroscopy (IMPS). The Bi2S3/WO3 films prepared via an in situ approach have a greater transient time constant and higher electron transit rate. This is most likely due to less interfacial defects for the Bi2S3/WO3 films prepared via an in situ approach, resulting in a lower resistance and faster carrier transport in the interface between WO3 and Bi2S3.

Construction of novel Bi2S3 nanobelt @ WO3 nanoplate arrays on FTO glass with high photoelectrochemical activity

In this work, a novel Bi2S3 nanobelt/WO3 nanoplate array film was prepared firstly by a facile two-step hydrothermal method with a successive annealing treatment. The as-prepared sample was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD) and ultraviolet visible spectrometry (UV–vis). The results show that Bi2S3 nanobelts epitaxially grow on the surface of WO3 nanoplates and the films have an excellent visible light absorption performance. Moreover, when investigated as photoanode for photoelectrochemical (PEC) cells, such novel Bi2S3 nanobelt @ WO3 nanoplate photoanodes exhibited a high PEC activity and generated a photocurrent density of 8.91 mA cm−2 at −0.1 V vs. Ag/AgCl in the electrolyte solution containing 0.1 M Na2SO3 and 0.1 M Na2S. The remarkable PEC activity of the photoanode may be ascribed to the efficient charge transfer and increased surface areas in the photoelectrode.