BiVO4 Thin Film Research Articles

Sustainable dual-cathode photoelectro-Fenton-like system at a wide pH range for rapid degradation of emerging pollutants

In-situ Fenton like process was highly promising and energy-efficient for treating emerging organic contaminants. However, the challenge in the production and activation of H2O2 faces its practical application. Herein, a photoelectro-Fenton-like (PEF) system was successfully fabricated with BiVO4 thin-film, graphite (C) and PhC2Cu as photoanode, cathode and photocathode, respectively. The ternary system was applied for visible-light degradation of Tetracycline (TC) at a low potential of 0.5 V. H2O2 was generated at the graphite cathode and then activated to produce •OH by Cu(I) from PhC2Cu photocathode. The photo-generated electrons accelerated the Cu(I)/Cu(II) cycle to achieve sustainable PEF reactions. After 150 min of illumination, 97 % TC was degraded in BiVO4|C|PCu system, superior to BiVO4|C and BiVO4|PCu systems. The outstanding stability and reusability of this PEF system was proved by 10 cycles. Moreover, the vulnerable atomic sites of TC molecule were predicated by the Fukui function. Both inhibition zone tests of bacteria and wheat seeds cultivation experiments proved that the constructed PEF system displayed outstanding performance in hampering TC eco-toxicity. For example, the Fv/Fm fluorescence image map demonstrated that the constructed PEF system not only degraded organic pollutants but also lowered their toxicity. Finally, the mechanism of in-situ generation and activation of H2O2 was proposed based on the results of quenching experiments, PL spectra and ESR technique. Overall, this study provides a promising pathway to remediate environmental pollution through constructing a PEF system based on dual cathodes.

Phenyl-C61-butyric acid methyl ester (PCBM) nanoparticle mediated boasting of photoelectrochemical and photocatalytic properties of bismuth vanadate/lead sulphide (BiVO4/PbS) composite thin-film

This work delineates the fabrication and characterization of BiVO4/PbS and BiVO4/PCBM/PbS-based composite heterostructure for visible-light-driven applications, such as pollution remediation, photoelectrochemistry (PEC), and applied bias to photoelectrochemical hydrogen generation efficiency (ABPE). The heterostructured composite was synthesized by a combination of Spin coating (for bismuth vanadate - BiVO4 thin film fabrication and PCBM deposition), and Successive Ionic Layer Absorption and Reaction -SILAR (for lead sulphide - PbS deposition) method and characterized using UV–visible Spectroscopy, time-resolved photoluminescence spectroscopy (TRPL), field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), and photoelectrochemistry (PEC) analysis (PEC). The key benefit of incorporation of PCBM nanoparticles in BiVO4/PCBM/PbS was realized through 1) ∼ 70 % improvement in the photocurrent density during electrochemistry analysis, 2) ∼ 2.3 times enhancement in ABPE, and 3) ∼ 43 % enhancements in ‘rate constant’ towards photocatalytic (methylene blue) degradation compared to BiVO4/PbS. The work shows the benefits of the PCBM-conductive carbon-based electron transport layer as a bridge between two inorganic semiconductors (BiVO4 and PbS) towards enhancing fast electron separation and transport at the interface during visible light irradiation.

SnS2 Nanoparticles Embedded in BiVO4 Surfaces via Eutectic Decomposition for Enhanced Performance in Photoelectrochemical Water Splitting.

BiVO4 has garnered substantial interest as a promising photoanode material for photoelectrochemical water-splitting due to its narrow band gap and appropriate band edge positions for water oxidation. Nevertheless, its practical use has been impeded by poor charge transport and sluggish water oxidation kinetics. Here, a hybrid composite photoanode is fabricated by uniformly embedding SnS2 nanoparticles near the surface of a BiVO4 thin film, creating a type II heterostructure with strong interactions between the nanoparticles and the film for efficient charge separation. This structure forms via eutectic melting during atomic layer deposition of SnS2 with subsequent phase separation between SnS2 and BiVO4 at room temperature, offering greater advantages and flexibilities over conventional exsolution techniques. Furthermore, the SnS2/BiVO4 hybrid composite is coated with a thin amorphous ZnS passivation layer to accelerate charge transfer process and enhance long-term stability. The optimized BiVO4/SnS2/ZnS photoanode exhibits a photocurrent density of 5.44mAcm-2 at 1.23V versus RHE, which is 2.73 times higher than that of the BiVO4 photoanode, and a dramatic improvement in photostability retention at 1.23V versus RHE, increasing from 55% to 91% over 24 hours. This method of anchoring nanoparticles onto host materials proves highly valuable for energy and environmental applications.

High transmittance BiVO4 thin-film photoanodes by reactive magnetron sputtering for a photovoltaic-photoelectrocatalysis water splitting system

As the system with the highest solar hydrogen conversion efficiency, the further improvement of photovoltaic-photoelectrocatalysis (PV-PEC) efficiency is dependent on the light transmittance, activity and stability of the photoanode. Here, a highly permeable BiVO4 thin film was fabricated through controlled magnetron sputtering. The thickness of the thin film was merely 345 nm, while its transmittance in the visible light range reached as high as 70%. Moreover, large-scale production of such films could be achieved. By incorporating NiFeOx oxygen extraction cocatalyst, under AM 1.5G illumination, the photocurrent density at 1.23 V on reversible hydrogen electrode (RHE) increased to 4.2 mA cm−2 and the incident photon-current conversion efficiency reached 70%. A PV-PEC system was designed to efficiently harness sunlight by integrating the photoanode with a solar photovoltaic panel. Upon connection with the solar photovoltaic panel (with an efficiency of only 7%), spontaneous water decomposition could be achieved, resulting in a solar-to-hydrogen conversion efficiency (ηSTH) of 4.2% for the series system. This study contributes to the realization of cost-effective and highly efficient PV-PEC hydrogen production.

Effect of annealing temperature on bismuth vanadate nano thin films for solar cell applications

Bismuth vanadate (BiVO4) has been used as the photoanode electrodes in ferroelectric solar cells owing to its unique combination of properties: a narrow bandgap among ferroelectrics, economic viability, negative conduction band edge, and remarkable stability. The present work explores the fabrication and characterization of BiVO4 thin films prepared via spin coating, with a specific focus on elucidating the influence of the annealing temperature (400–550 °C) on their structural, optical, and photovoltaic properties. From X-ray diffraction (XRD) analysis, it is observed that higher annealing temperatures have promoted the formation of larger grains, enhanced crystallinity, and induced a preferred crystal orientation characteristic of the monoclinic scheelite structure. Tauc plot analysis shows the dependence of the optical band gap on the annealing temperature for BiVO4 thin films. The band gap values have decreased slightly from 2.50 eV at 400 °C to 2.44 eV at 550 °C. This is indicated by the slightly narrowed bandgap, which influences the structure of the material or defect states at higher annealing temperatures. A narrower bandgap allows for the absorption of lower-energy light, potentially improving the light absorption efficiency of BiVO4 thin films in photoanode applications. The influence of annealing temperature on BiVO₄ thin film solar cell performance was investigated further through the analysis of open-circuit voltage (Voc), short-circuit current (Isc) and power conversion efficiency.

Suppressing Carrier Recombination in BiVO4/PEDOT:PSS Heterojunction for High-Performance Photodetector.

The organic-inorganic hybrid heterojunction is introduced for the first time to break through the performance bottleneck of BiVO4-based photodetectors. Through a facile solution process, a p-n heterojunction is established at the BiVO4/PEDOT:PSS interface, and the built-in electric field is designed to separate photogenerated charge carriers. The hybrid heterojunction outputs a significantly increased photocurrent, which is 24 000 times larger than that of the bare BiVO4 thin film. The photodetector shows a satisfactory performance with a responsivity (R) and specific detectivity (D*) of 107.8 mA/W and 4.13 × 1010 Jones at 482 nm illumination. In addition to the fast response speed (100 ms), the device also exhibits an impressive long-term stability with a negligible attenuation in photocurrent after more than 700 cycles. This work provides a novel strategy to suppress carrier recombination of BiVO4, and the coupling of metal oxides and organic semiconductors opens up a new avenue for fabricating high-performance photodetectors.

Boosting the photoelectrochemical performance of bismuth vanadate photoanode through homojunction construction

The photoelectrochemical (PEC) performance of bismuth vanadate (BiVO4) suffers from sluggish charge mobility and substantial charge recombination losses due to its intrinsic defect. To rectify the problem, we developed a novel approach to prepare an n-n+ type II BVOac-BVOal homojunction with staggered band alignment. This architecture involves a built-in electric field that facilitating the electron-hole separation at the BVOac/BVOal interface. As a result, the BVOac-BVOal homojunction shows superior photocurrent density up to 3.6 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) with 0.1 M sodium sulfite as the hole scavenger, which is 3 times higher than that of the single-layer BiVO4 photoanode. Unlike the previous efforts that modifying the PEC performance of BiVO4 photoanodes through incorporating heteroatoms, the highly-efficient BVOac-BVOal homojunction was achieved without incorporating any heteroatoms in this work. The remarkable PEC activity of the BVOac-BVOal homojunction highlights the tremendous importance of reducing the charge recombination rate at the interface by constructing the homojunction and offers an effective strategy to form the heteroatoms-free BiVO4 thin film as an efficient photoanode material for practical PEC applications.

Spatially Resolved Optical Spectroscopic Measurements with Simultaneous Photoelectrochemical Mapping Using Scanning Electrochemical Probe Microscopy

A deep understanding of the properties of semiconductor films at the micro-/nanoscale level is fundamental toward designing effective photoelectrocatalysts. Here, we integrated spatially resolved optical spectroscopy (SR-OS) with scanning photoelectrochemical microscopy (SPECM) to collect UV/vis spectra and quantify photocurrents of localized sites on a nanostructured BiVO4 thin film. Direct measurement of absorbance allowed for the determination of band gap energy at each location. Absorbance and photocurrent maps were obtained and used to investigate heterogeneities on the films. Scanning electrochemical cell microscopy (SECCM) was also coupled with SR-OS to acquire quantitative photoelectrochemical data at the FTO/BiVO4 film interface, revealing higher photocurrents at the boundary regions. As a droplet-based technique, SECCM was employed to estimate the wetted area by measuring the maximum height of droplet stretch at each point, allowing for the calculation of photocurrent density. This novel approach provides an advantageous mean to correlate localized photocatalytic activities and band gap energies.

A novel BiVO4/DLC heterojunction for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is a promising technology to produce renewable hydrogen, which still faces problems of low photoelectric efficiency and instability. This work introduces a novel Type II heterojunction consisting of BiVO4 thin film and diamond-like carbon (DLC) to the PEC system as a photoanode and achieves an increased PEC water-splitting activity. Compared to the pure BiVO4, the BiVO4/DLC heterojunction has an increased photocurrent density from 0.79 mA cm−2 to 2.39 mA cm−2 at 1.23 V vs RHE, and the IPCE from 4.8 % to 23.4 %. After 120 min (180 cycles) of PEC water splitting, the BiVO4/DLC heterojunction retains up to 82.3 % of the initial photocurrent density value, while the pure BiVO4 has only 33.99 % remaining under the same conditions. Furthermore, the PEC system of BiVO4/DLC reaches the evolution rate of hydrogen of over 0.32 mmol h−1 cm−2, which is much higher than that of its counterparts. We ascribe the enhancement in PEC performance to the Type II heterojunction photoanodes that greatly promote carrier mobility and reduce the recombination rate of electron-hole pairs. We also identify that the band bending and depletion layer are the main reasons for the decrease in charge transfer and interface resistance. It is demonstrated that the sp2 carbon phase in DLC acts as a conductive channel to improve the separation and migration efficiency of free carriers, while the sp3 carbon phase provides stable support and passivation effect to the photoanode, thereby leading to an enhancement for both PEC water splitting performance and the long-time stability. This work provides an effective way to improve the BiVO4 photoanode-based PEC water-splitting systems.

Deposition of nanoporous BiVO4 thin-film photocatalyst by reactive magnetron sputtering: Effect of total pressure and substrate

Nanoporous BiVO4 thin films were deposited using reactive magnetron sputtering in Ar and O2 atmosphere, on various substrates, employing pulsed direct-current (DC) power supplies applied to metallic Bi and V targets for rapid deposition. The procedure was followed by a post-annealing treatment in air to crystallize the photoactive monoclinic scheelite structure. The influence of total pressure and substrate on the crystal structure, morphology, microstructure, optical and photocatalytic properties of the films was investigated. The crystallization of monoclinic scheelite structure deposited on fused silica substrate starts at 250 °C and the films are stable up to 600 °C. The morphology of the films is rather dense, despite at the high sputtering pressure (>2 Pa), with embedded nanopores. Among the thin films deposited on fused silica, the one deposited at 4.5 Pa exhibits the highest porosity (52%), with the lowest bandgap (2.44 eV) and it shows the highest photocatalytic activity in the degradation of Rhodamine-B (26% after 7 h) under visible light irradiation. The film deposited on the silicon substrate exhibits the highest photoactivity (53% after 7 h). Lack of hypsochromic shift in the UV−Vis temporal absorption spectra shows the dominance of the chromophore cleavage pathway in the photodecomposition.

Pinhole-Free Co-Pi /Bivo4 Thin Film with Continuous Interparticle Porosity for Improved Photoelectrochemical Water Oxidation

Pinhole-Free Co-Pi /Bivo4 Thin Film with Continuous Interparticle Porosity for Improved Photoelectrochemical Water Oxidation

SYNTHESIS OF BiVO4 THIN FILM AS PHOTOANODE WATER SPLITTING AND DYE DEGRADATION

Synthesis and characterization of BiVO4 thin film as photoanode of PEC water splitting and degradation of methylene blue had been successfully carried out. BiVO4 was obtained from the electrodeposition of BiOI and VO(acac)2. Variations in potential and deposition time were carried out to obtain optimum performance results. BiVO4 results from a potential of -0.2 V for 10 minutes gave the highest photocurrent. Characterization using XRD and SEM showed that the thin film had nanoporous properties. In addition, analysis with UV-Vis DRS obtained a band gap of 2.51 eV. The application of PEC water splitting was carried out with a tandem dual absorber system, BiVO4 as a photoanode, and CuInS2 photocathode providing an operating current of about 0.5 mA/cm2 . The effect of modification with FeOOH catalyst gave a lower photocurrent compared to using a hole-sacrificing agent. In addition, this system can also produce 99.7% degradation of methylene blue. This showed that BiVO4 had a good potency as PEC water splitting material for hydrogen production and dye waste degradation.

One-step preparation of Ag-incorporated BiVO4 thin films: plasmon-heterostructure effect in photocatalytic activity enhancement

Ag-incorporated BiVO4 thin film with high photocatalytic activity is a great candidate for industrial wastewater treatment, enhancing the photoactivity of BiVO4, as well as solving the recyclability and reusability drawback of powder photocatalysts. Therefore, a novel one-step process of the reactive magnetron sputtering technique was employed, which to this day was never utilized to synthesis Ag-incorporated BiVO4 thin films. The effect of Ag incorporation on the photocatalytic properties was comparatively investigated. The photoactive phases e.g. monoclinic BiVO4, Ag4V2O7, α-AgVO3 were detected by X-ray diffraction (XRD). Various morphologies, depending on the Ag content, were observed by field emission electron microscopy (FESEM) along with Ag nanoparticles on the film surface. X-ray photoelectron spectroscopy (XPS) proved the existence of Bi and V exclusively in their Bi+3 and V+5 oxidation states, while Ag was present in Ag+ and Ag0, which are correspondent with silver vanadates and Ag nanoparticles, respectively. The thin film with 24 at. % Ag exhibited superior photocatalytic performance with a 99 % photodegradation of Rhodamine-B at neutral pH under visible light, as a result of having the lowest bandgap (1.96 eV), proper distribution of Ag4V2O7 phase, the plasmonic effect of Ag nanoparticles on the film surface, and the lower recombination rate compared to the pristine sample demonstrated by photoluminescence (PL) spectra. The recyclability experiment ensured the high stability of the thin films after three consecutive cycles, and the role of superoxides (•O2−) and photogenerated holes were found to be crucial using scavengers. The results confirmed the synergistic enhancement of the photocatalytic activity through Ag-incorporated BiVO4 heterostructure and the plasmonic effect, as well as solving the low photoactivity of BiVO4 at neutral pH.

Temperature Effect on Photoelectrochemical Water Splitting: A Model Study Based on BiVO4 Photoanodes.

Photoelectrochemical (PEC) water splitting is typically studied at room temperature. In this work, the temperature effect on PEC water splitting is studied using crystalline BiVO4 thin film photoanode as a model system. Systematic temperature-dependent electrochemical study demonstrates that the PEC activity is boosted at elevated electrolyte temperatures and indicates that thermal energy plays a main role in improving charge carrier transport in the bulk of BiVO4. Irreversible surface reconstruction is observed after PEC reactions at elevated temperature in the presence of hole scavengers, with regularly spaced stripes emerging on BiVO4 grains. The surface-reconstructed photoanode exhibits up to 40% improvement in photocurrent densities and ∼ 0.25 V shift of photocurrent onset to favorable direction. Detailed investigation shows the formation of an amorphous layer without stoichiometric change at the reconstructed surface. This work provides insights of the temperature effect on the photoelectrode in solar water splitting and reveals the non-negligible effect of hole scavengers in photoelectrochemical measurement.

Highly practical and reproducible BiVO4 thin film fabrication using automatic dip-coating machine towards for photoelectrocatalytic activities improvement

ABSTRACT This research developed a simple method for bismuth vanadate (BiVO4) thin film using an automatic dip-coating method. A precursor solution concentration, dipping speed, and calcination temperature were optimized to obtain the highest photoelectrocatalytic (PEC) BiVO4 electrode for water oxidation. The BiVO4 electrode was applied to organic dye degradation and studied the catalytic mechanism at the electrode surface. A calcination temperature of 450 °C was optimized for BiVO4 photoanode preparation for the highest PEC water oxidation and had good charge transfer process properties. The proposed automatic dip-coating method presents high efficiency for the large scale of BiVO4 electrode fabrication, and it was highly reproducible at a low relative standard deviation of less than 5%. The developed BiVO4 electrode can eliminate methyl red organic dyes by more than 70% within 1 hour. This research offers a new alternative approach for a simple, convenient, reproducible, and scaled-up method for semiconductor thin film fabrication.

Enhanced photocatalytic activity of sputter-deposited nanoporous BiVO4 thin films by controlling film thickness

In this study, nanoporous BiVO4 thin films were deposited using reactive direct-current (DC) magnetron sputtering. The effects of thickness on the film morphology, crystal structure, microstructure, composition, optical and photocatalytic properties under visible light were investigated. The film porosity and refractive index were also determined via the UV-Vis spectrophotometric technique using transmittance and reflectance spectra and Cauchy dispersion law as the fitting model. The nanoporous morphology was observed using field-emission scanning electron microscopy (FESEM) with average pore sizes in the 20–40 nm range. The X-ray diffraction (XRD) results showed different texture grades corresponding to the (040) crystallographic plane, establishing the film thickness influence on the preferential orientation. The X-ray photoelectron spectroscopy (XPS) was also implemented to investigate the chemical state of the film surface, as well as to determine the valence band position. The film 715 nm in thickness showed the highest porosity (52%), narrowest bandgap (2.44 eV), highest exposed (040) crystallographic plane and highest visible-light-driven photodegradation towards Rhodamine-B (RhB) solution. The pH of the solution also impacted the RhB photodegradation which was optimum at pH 3 with chromophore cleavage pathway dominance, whereas at neutral pH it had distinctively slow kinetics probably due to poor electrostatic interactions and the N-deethylation kinetics bottleneck. The photocatalytic cycle experiments exhibited high stability and recyclability of BiVO4 thin-film photocatalysts after four cycles (4 ×7 h) of exploitation. The photocatalytic mechanism was determined using scavengers and the significance of hydroxyl radicals and photogenerated holes were established. The photocatalytic activity reached 97% after 7 h of illumination with a 400 W light source.

A versatile synthesis strategy and band insights of monoclinic clinobisvanite BiVO4 thin films for enhanced photoelectrochemical water splitting activity

Monoclinic clinobisvanite BiVO4 is one of the promising and extensively researched material for photoelectrochemical (PEC) water splitting. However, no substantial progress has been made to tune the morphology and to explore a wide range of dopants to BiVO4 and heterojunction systems that could affect its PEC activity. Given this, here we propose a versatile BiVO4 thin film synthesis strategy that allows morphology tunability, the feasibility of doping, and heterojunction formation in a single step. The presence of the monoclinic phase was confirmed, and detailed PEC and spectroscopic properties were evaluated to explore water splitting activity and band edge insights. The strategy was extended to fabricate different nanostructures by changing the capping agents and demonstrated the feasibility of Al doping and heterojunction formation with WO3 nanostructure for enhanced PEC activity. Importantly, the proposed strategy could be exploited using new capping agents and dopants for simultaneously obtaining doped BiVO4 in heterojunction systems having unique morphology.

Effect of Radio-Frequency Power on the Composition of BiVO4 Thin-Film Photoanodes Sputtered from a Single Target

BiVO4 films were fabricated by radio frequency (RF) sputtering from a single target. The deposited BiVO4 films were found to be rich in Bi, and the reason for the Bi-richness was investigated. It was inferred from the Monte Carlo simulation that, during sputtering, the transfer process of target atoms through argon gas played a major role in this phenomenon. The transfer process resulted in an imbalanced ratio of Bi and V, arising from the difference in atom mass and interaction radius. The high RF power was found to be effective in adjusting the Bi/V ratio, influencing the sputtering yield. This type of preferential sputtering was maintained by the diffusion of target atoms from the bulk to the surface. BiVO4 films with monoclinic scheelite crystal structures were obtained at high RF power values and found to exhibit photocatalytic performances beneficial for photoanodic applications.

Role of Alkali Metal in BiVO4 Crystal Structure for Enhancing Charge Separation and Diffusion Length for Photoelectrochemical Water Splitting.

Alkali metal (Na or K) doping in BiVO4 was examined systematically for enhancing bulk charge separation and transport in addition to improving charge transfer from the surface. The alkali metal-doped BiVO4 thin film photoanodes having nanostructured porous grain surface morphology exhibited better photocurrent density than pristine BiVO4. In particular, Na:BiVO4/Fe:Ni/Co-Pi photoanode showed a significantly improved photocurrent of 3.2 ± 0.15 mA·cm-2 in 0.1 M K2HPO4 electrolyte at 1.23 VRHE under 1 sun illumination. The depth-dependent Doppler broadening spectroscopy measurements confirmed the significant reduction in Bi- and V-based defect density with Na metal doping, and this led to a higher bulk diffusion length of charge pairs (four times that of the pristine one). Na doping led to reduced surface defects resulting in improved surface charge transfer based on cyclic voltammetry experiments. The density functional theory calculations confirmed the improved performance in Na-doped BiVO4 photoanodes achieved through interband formation and reduction in the band gap.

Bismuth vanadate thin films for efficient photoelectrochemical water splitting

Monoclinic bismuth vanadate has attracted much attention as one of the efficient photoanode materials that can harvest a wide range of visible light to split water efficiently. In this study, we report the preparation of nanoporous BiVO4 via wet chemical approach coupled with dip-coating technique. The monoclinic scheelite phase of BiVO4 is revealed by X-ray diffraction (XRD). Characterisation techniques like Raman spectroscopy, diffuse reflectance spectroscopy (DRS) and scanning electron microscopy (SEM) have been analysed and confirmed the formation of BiVO4 layers on FTO. Photoelectrochemical studies of BiVO4 thin films have been performed in a three-electrode potentiostat system, illuminated under visible light-emitting diode (LED) source of intensity 100 mW/cm2. The optimised 10 layered BiVO4 thin film with average thickness of ~ 300 nm shows an optimum photocurrent density of ~ 0.67 mA/cm2 at 1.23 V vs RHE and photoconversion efficiency of 0.4% at 1.23 V vs RHE as compared with different layered BVO photoanodes. The measurements of flat band potential and confirmation of n-type behaviour of BiVO4 semiconductors were carried out by Mott–Schottky analysis. Electrochemical impedance spectroscopy (EIS) study clearly indicate the less charge transfer resistance and high hole transfer mobility of optimised BiVO4 photoanode films.