Bare BiVO4 Research Articles

Boosting the Photoactivity of BiVO4 Photoanodes by a ZnCoFe-LDH Thin Layer for Water Oxidation.

Monoclinic bismuth vanadate (BiVO4 ) has been used as an efficient photoanode material for photoelectrochemical water oxidation owing to its suitable band gap and nontoxicity. Nevertheless, the practical application of BiVO4 photoanode has been severely limited by the surface charge recombination and sluggish kinetic, which leads to the obtained photoactivity of BiVO4 is much lower than its theoretical value. In this case, ZnCoFe-LDH thin layer is conformally decorated on the porous BiVO4 photoanode through a simple electrodeposition process. The results show that a boosted photoactivity and a remarkably enhanced photocurrent density (3.43 mA cm-2 at 1.23 VRHE ) are attained for BiVO4 /ZnCoFe-LDH. In addition, the optimized BiVO4 /ZnCoFe-LDH photoanode exhibits significant negative shift in the onset potential (0.51 VRHE to 0.21 VRHE ), promotes charge separation efficiency (49.3% to 60.4% in the bulk, 29.6% to 61.9% on the surface at 1.23 VRHE ) and enhanced IPCE efficiency (25.5% to 54.7% at 425 nm) compared with that of bare BiVO4 photoanode. It is demonstrated that the boosted photoactivity of BiVO4 /ZnCoFe-LDH photoanode is mainly ascribed to the synergy effects of the formation of p-n heterojunction between ZnCoFe-LDH and BiVO4 to accelerate the photogenerated charge transfer and separation, broaden light absorption, as well as promote the surface water oxidation kinetics.

Room chemical bath temperature deposition of Mn:FeOOH on BiVO4 photoanode to enhance water oxidation

BiVO4 is one of the substrates that have received wide attention from researchers for photoelectrochemical (PEC) water oxidation due to its narrow band gap and sufficiently upbeat valence band. In this study, Mn-FeOOH cocatalyst was synthesized on the BiVO4 photoanode by a chemical bath deposition method at room temperature. As water oxidation cocatalyst, FeOOH could oxidize H2O to O2 kinetically easier. Furthermore, the Mn element mixing increases the active sites, leading to a faster charge transfer rate by decreasing the kinetics barrier, and it can act as a passivation layer to suppress electron-hole recombination. The results show that the photocurrent density of Mn-FeOOH/BiVO4 is 1.4 mA cm-2 (1.23 VRHE), which is 2.3 folds that of the bare BiVO4 electrode (0.6 mA cm-2), and the onset potential is also negatively shifted by 130 mV and provides a new idea for the design of photoelectrodes.

Suppressing photoinduced charge recombination at the BiVO4||NiOOH junction by sandwiching an oxygen vacancy layer for efficient photoelectrochemical water oxidation

Nickel oxyhydroxide (NiOOH) is regarded as one of the promising cocatalysts to enhance the catalytic performance of photoanodes but suffers from serious interfacial charge-carrier recombination at the photoanode||NiOOH interface. In this work, surface-engineered BiVO4 photoanodes are fabricated by sandwiching an oxygen vacancy (Ovac) interlayer between BiVO4 and NiOOH. The surface Ovac interlayer is introduced on BiVO4 by a chemical reduction treatment using a mild reducing agent, sodium hypophosphite. The induced Ovac can alleviate the interfacial charge-carrier recombination at the BiVO4||NiOOH junction, resulting in efficient charge separation and transfer efficiencies, while an outer NiOOH layer is coated to prevent the Ovac layer from degradation. As a result, the as-prepared NiOOH-P-BiVO4 photoanode exhibits a high photocurrent density of 3.2 mA cm−2 at 1.23 V vs. RHE under the irradiation of 100 mW/cm2 AM 1.5G simulated sunlight, in comparison to those of bare BiVO4, P-BiVO4, and NiOOH-BiVO4 photoanodes (1.1, 2.1 and 2.3 mA cm−2, respectively). In addition to the superior photoactivity, the 5-h amperometric measurements illustrate improved stability of the surface-engineered NiOOH-P-BiVO4 photoanode. Our work showcases the feasibility of combining cocatalysts with Ovac, for improved photoactivity and stability of photoelectrodes.

Creation of oxygen vacancies to activate 2D BiVO4 photoanode by photoassisted self‐reduction for enhanced solar‐driven water splitting

BiVO4 is regarded as a promising photoanode material because of its narrow band gap (∼ 2.4 eV). However, the poor bulk carrier transport capacity severely limits the actual performance of BiVO4 in photoelectrochemistry (PEC) water splitting. Here, we tried to synthesize two-dimensional (2D) morphology by adding structure-directing agents to hydrothermal solution and introduce oxygen vacancies by photoassisted self-reduction. In the scheme, the 2D morphology can shorten the carrier diffusion length and the construction of oxygen vacancies can increase the bulk carrier concentration. Through the combined effect of both, the inherent poor carrier transport capacity of BiVO4 has been improved, which has been proven by Electrochemical Impedance Spectroscopy (EIS), Intensity Modulated Photocurrent Spectroscopy (IMPS) and Mott-Schottky (M-S) plots. At 1.23 V vs. RHE, the photocurrent density increases from ∼1.60 mA/cm2 (2D BiVO4) to ∼2.30 mA/cm2 [2D BiVO4(Vox)], which is 8 times larger than that of bare BiVO4(0.3 mA/cm2). The incident photon-to-current efficiencies (IPCE) of 2D BiVO4(Vox) have reached the value of 46% (at 350 nm). The carrier separation efficiency (ƞsep) and carrier injection efficiency (ƞinj) have been improved up to 49% and 68%, respectively.

Decoration of BiVO4 Photoanodes with Near-Infrared Quantum Dots for Boosted Photoelectrochemical Water Oxidation.

Broadening light absorption and improving charge carrier separation are very critical to boost the water splitting efficiency in photoelectrochemical (PEC) systems. We herein reported a heterostructured photoanode consisting of BiVO4 and eco-friendly, near-infrared (NIR) CuInSeS@ZnS core-shell quantum dots (QDs) for PEC water oxidation. The decoration of core-shell QDs concurrently extends the absorption range of BiVO4 from the ultraviolet-visible to NIR region and promotes the effective separation and transfer of photo-excited electrons and holes. Without any sacrificial agents and co-catalysts, the as-fabricated NIR core-shell QDs/BiVO4 heterostructured photoanodes exhibit an approximately fourfold higher photocurrent density than that of the bare BiVO4, up to 3.17 mA cm-2 at 1.23 V versus the reversible hydrogen electrode. It is revealed that both a suitable band alignment and an intimate interfacial junction between QDs and BiVO4 are the main factors that result in enhanced charge separation and transfer efficiencies. We also highlight that the NIR CISeS QDs passivated with a ZnS shell can suppress the non-radiative recombination and enhance the stability of the QD photoanodes for optimized PEC performance. This work provides a facile and effective approach to boost the water oxidation efficiency of semiconductor photoanodes via utilizing NIR core-shell QDs as a light sensitizer and charge carrier separator.

Facile fabrication of BiVO4/Bi2S3/NiCoO2 for significant photoelectrochemical water splitting

For photoelectrochemical (PEC) water splitting, BiVO4 is the most efficient light-absorber metal oxide; nevertheless, significant charge recombination and low water oxidation kinetics have been restricted its effectiveness. Therefore the idea of creating heterojunction by using metal sulfide followed by the decoration of catalyst were employed to obtain the ideal water splitting performance of the photoelectrode. In this study simple and unique strategy is developed to fabricate BiVO4/Bi2S3/NiCoO2 photoelectrode through facile and scalable solution route. Structural, morphological and optical analysis shows the stepwise fabrication of Bi2S3 and NiCoO2 upon BiVO4. BiVO4/Bi2S3/NiCoO2 composite demonstrates ∼5.5 times higher photocurrent density than bare BiVO4 with cathodic shift of ∼220 mV and greatly stable in 0.5 M Na2SO4electrolyte. Photoelectrochemical studies involving (i) estimation of flat band position, (ii) charge transfer resistance from impedance studies (iii) prediction of band alignment and (iv) significant increase in the injection efficiency and separation efficiency together signifies the importance of the NiCoO2 and Bi2S3 in the BiVO4/Bi2S3/NiCoO2 photoanode that emphasize superb PEC water splitting performance.

Crystal facet engineering of BiVO4/CQDs/TPP with improved charge transfer efficiency for photocatalytic water oxidation

BiVO4 as an outstanding semiconductor material has been extensively employed in artificial photosynthesis, but it usually suffers drawbacks such as poor electron transportation and slow kinetics of oxygen evolution. Herein, we construct a novel ternary BiVO4/CQDs/TPP photocatalysts for photocatalytic water oxidation by controlling the preferential growth of BiVO4 (010) crystal surface after introducing TPP. The BiVO4/CQDs/TPP shows an enhancement of the water oxidation rate of 352.5 μmol g−1h−1 compared with the bare BiVO4 (113.7 μmol g-1h−1), which is due to the more efficient interfacial electron-hole transfer between TPP and BiVO4 via CQDs as an electron mediator as well as preferentially exposed (010) facets of BiVO4. The efficient photogenerated charge behavior is confirmed by the surface photovoltage and transient absorption spectroscopy. Density functional theory calculation reveals that water dissociation on the (010) facet surface is more energetically favorable for BiVO4/CQDs/TPP-60 than that of the pristine BiVO4. The present work affords deep understanding of the crystal morphology and facet engineering for BiVO4-based photocatalysts.

Dimensional matched ultrathin BiVO4/Ti3C2Tx heterosystem for efficient photocatalytic conversion of CO2 to methanol

Dimensional matched ultrathin BiVO4/Ti3C2Tx MXene 2D/2D heterosystem is developed via a facile electrostatic self-assembly process. The composite shows an increased CO2 uptake capacity than that of the bare BiVO4 nanosheets. Besides, the well collaborated 2D/2D heterogeneous structure efficiently promotes the photoexcited charge transfer and separation. As a result, the photocatalytic CH3OH production rate of the BiVO4/Ti3C2Tx hydrid can reach 20.13 μmol g−1h−1, which is 4.1 times of the pristine BiVO4.

Photoelectrocatalytic degradation of caffeine using bismuth vanadate modified with reduced graphene oxide

Bismuth vanadate modified with reduced graphene oxide (BiVO4/rGO) was synthesized with the aim of applying this semiconductor material in advanced oxidative processes (AOPs) using the photoelectrocatalytic properties of the material for caffeine degradation. The semiconductor material was characterized by Scanning electronic microscopy, X-ray diffraction, Raman spectroscopy and UV–Vis Diffuse reflectance spectrophotometry. Photo-assisted linear sweep voltammetry experiments were carried out in order to evaluate the photocurrent generated in the processes. BiVO4/rGO was found to exhibit relatively better photoelectrocatalytic performance compared to bare BiVO4; this result confirms the fundamental role of the carbon-based material when it comes to photoanode construction. With regard to caffeine degradation by high performance liquid chromatography through the application of BiVO4/rGO photoanode, the signal used for monitoring the presence of the analyte exhibited a decrease of 100% of caffeine concentration from the original concentration, indicating the efficient removal of the compound from the sample.

An effective route for growth of WO3/BiVO4 heterojunction thin films with enhanced photoelectrochemical performance

The unsatisfactory solar light absorption of WO3 and poor charge separation of BiVO4 are main limits for their use in photoelectrochemical (PEC) water oxidation. Coupling WO3 with BiVO4 has been considered as a feasible way to improve PEC performance by taking complementary advantages of them. In this work, we obtained nanoflake-structured WO3 by hydrothermal growth with post-annealing. The effect of process variables on morphology and resultant performance were investigated. Electrodeposition growth was utilized to deposit BiVO4 onto WO3 forming WO3/BiVO4 heterojunction thin films. Porous BiVO4 with wormlike morphology was tightly coupled and well-distributed onto WO3 nanoflakes. The optimized best-performing WO3/BiVO4 photoanode exhibits higher photocurrent density than that summation of bare WO3 and BiVO4 over entire range of applied potential. This enhancement is mainly attributed to the effective charge separation at WO3/BiVO4 interface, which is confirmed through electrochemical impedance spectra (EIS) measurements, respectively. Our work provides a referable approach for the growth of WO3/BiVO4 heterojunction photoanode with enhanced PEC performance.

Co-catalytic effects of Bi-based metal-organic framework on BiVO4 photoanodes for photoelectrochemical water oxidation

Metal-organic frameworks (MOFs) are promising co-catalysts for increasingenhancing the performance of photoelectrochemical (PEC) water splitting. In this work, we successfully fabricated an efficient BiVO4 photoanode for PEC water oxidation by decorating its surface with Bi-based MOF as a co-catalyst via an unconventional immersion process at an ambient temperature. Bi-MOF exhibits a large surface area and promotes bulk charge separation and surface charge transfer in the water oxidation reaction, resulting in an enhancement in the photocurrent density, which is approximately two times larger than that of the bare BiVO4 photoanode. In addition, the operation stability of our Bi-MOF/BiVO4 photoanode was dramatically improved, and more than 95% of its initial photocurrent density was retained even after 24 h, indicating that the improved charge transfer by the Bi-MOF layer prohibits the dissolution of the BiVO4 layer into the solution during the water oxidation reaction.

Nanoscale Assembly of BiVO4/CdS/CoOx Core–Shell Heterojunction for Enhanced Photoelectrochemical Water Splitting

Porous BiVO4 electrodes were conformally decorated with CdS via a chemical bath deposition process. The highest photocurrent at 1.1 V vs. RHE was achieved for a BiVO4/CdS composite (4.54 mA cm−2), compared with CdS (1.19 mA cm−2) and bare BiVO4 (2.1 mA cm−2), under AM 1.5G illumination. This improvement in the photoefficiency can be ascribed to both the enhanced optical absorption properties and the charge separation due to the heterojunction formation between BiVO4 and CdS. Furthermore, the BiVO4/CdS photoanode was protected with a CoOx layer to substantially increase the photostability of the material. The new BiVO4/CdS/CoOx nanostructure exhibited a highly stable photocurrent density of ~5 mA cm−2. The capability to produce O2 was locally investigated by scanning photoelectrochemical microscope, which showed a good agreement between photocurrent and O2 reduction current maps. This work develops an efficient route to improve the photo-electrochemical performance of BiVO4 and its long-term stability.

Hydrogen bonded metal–organic supramolecule functionalized BiVO4 photoanode for enhanced water oxidation efficiency

Hydrogen bonded metal–organic supramolecules are a new family of cocatalysts for high-efficiency water oxidation photoanodes owing to their suitable electrical conductivity. We herein designed a calix[4]resorcinarene-based metal–organic supramolecular system with rich hydrogen bonds, namely [Cu2L(H2O)2]∙3DMF (L = calix[4]resorcinarene-based ligand and DMF = N,N’-dimethylformamide) or Cu2L. Then, the hydrogen bonded metal–organic supramolecular system was applied as a cocatalyst in BiVO4 nanoplate photoanode for water oxidation reaction. Photoelectrochemical and electrochemical analysis demonstrated that the obtained Cu2L-modified BiVO4 photoanode showed greatly enhanced water oxidation efficiency, which was about three times higher than bare BiVO4 nanoplates. In addition, photoelectrochemical activity was well maintained within three hours. Cu2L as an efficient cocatalyst can promote the holes on the surface of the photoanode to participate in the oxygen evolution reaction, thus improving the performance of the photoanode. This work presents a feasible strategy by using the hydrogen bonded metal–organic supramolecular system to functionalize photoanodes for enhanced water oxidation efficiency.

Deposition of zinc cobaltite nanoparticles onto bismuth vanadate for enhanced photoelectrochemical water splitting

During the past few decades, photoelectrochemical (PEC) water splitting has attracted significant attention because of the reduced production cost of hydrogen obtained by utilizing solar energy. Significant efforts have been invested by the scientific community to produce stable ternary metal oxide semiconductors, which can enhance the stability and increase the overall production of oxygen. Herein, we present the ternary metal oxide deposition of ZnCo2O4 as a route to obtain a novel photocatalyst layer on BiVO4 to form BiVO4/ZnCo2O4 a novel composite photoanode for PEC water splitting. The structural, topographical, and optical analyses were performed using field emission scanning electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy, and UV–Vis spectroscopy to confirm the structure of the ZnCo2O4 grafted over BiVO4. A remarkable 4.4-fold enhancement of the photocurrent was observed for the BiVO4/ZnCo2O4 composite compared with bare BiVO4 under visible illumination. The optimum loading of ZnCo2O4 over BiVO4 yields unprecedented stable photocurrent density with an apparent cathodic shift of 0.46 V under 1.5 AM simulated light illumination. This is also evidenced by the flat-band potential change through Mott–Schottky analysis, which reveals the formation of p-ZnCo2O4 on n-BiVO4. The improvement in the PEC performance of the composite with respect to bare BiVO4 is ascribed to the formation of thin passivating layer of p-ZnCo2O4 on n-BiVO4 which improves the kinetics of interfacial charge transfer. Based on our study, we have gained an in-depth understanding of the BiVO4/ZnCo2O4 composite as high potential in efficient PEC water splitting devices.

Decoration of AgOx hole collector to boost photocatalytic water oxidation activity of BiVO4 photoanode

BiVO4 is a promising light harvester for the construction of photoanode for solar-driven water splitting, but it suffers from low charge mobility and slow oxygen evolution reaction kinetics. Herein, we report on a novel strategy using AgOx (e.g. Ag2O and AgO) nanoparticles as hole collectors to boost the BiVO4 photoanode to its best photocatalytic performance. AgOx helps to boost the charge transfer efficiency at the BiVO4/electrolyte interface up to 93%, being much higher than 40% achieved for a bare BiVO4 photoanode. AgOx also contributes to improving the photostability of BiVO4 by offering an efficient quenching of the photogenerated holes, which are harmful to the BiVO4, e.g. causing an oxidative dissolution of V. In a pH 7 phosphate buffer electrolyte and under 1 sun illumination, the best BiVO4/AgOx photoanode generates a photocatalytic current density of 4.65 mA/cm2 at 1.23 V vs. reversible hydrogen electrode. It represents a 2.3-fold improvement of activity in comparison to a bare BiVO4 without AgOx decoration. The current BiVO4/AgOx can be placed among the top-tier photoanodes for solar water splitting made of BiVO4 light harvester.

An Inorganic–Organic Hybrid Polymer Cocatalyst for Photoelectrochemical Water Oxidation with Dual Functions of Accelerating Kinetics and Improving Charge Transfer

Oxygen evolution cocatalysts (OECs) play important roles in improving the efficiency of photocatalysts in solar water splitting. Inorganic–organic hybrid polymers (IOHPs), which have good electroly...

Effect of SILAR-anchored ZnFe2O4 on the BiVO4 nanostructure: An attempt towards enhancing photoelectrochemical water splitting

Development of high performance photoanodes for application in solar-driven photoelectrochemical cells is considered a grand challenge. Various structures and materials have been studied to overcome the current performance limit of the photoanode in photoelectrochemical cells; however, the enhancement in both stability and photocurrent has not been realized to date. In our study, the successive ionic layer adsorption and reaction method is used to coat ZnFe2O4 nanoparticles on the BiVO4 photoanodes. Various characterizations about structural, morphological, and optical characterizations confirm the presence of anchored ZnFe2O4 nanoparticles over BiVO4. Showing remarkable stability, the photocurrent density of optimized BiVO4/ZnFe2O4 is significantly increased compared with that of the bare BiVO4 nanostructured thin film. Mott-Schottky and electrochemical impedance spectroscopy analyses demonstrate that the appropriate number of the successive ionic layer adsorption and reaction cycles leads to efficient charge transfer. Furthermore, the correlation among structural, morphological and optical properties is discussed here.

High photocatalytic activity of magnetic composite photocatalyst NiFe2O4/BiVO4 for rhodamine b degradation under visible led light irradiation

To improve the photocatalytic activity of BiVO4 semiconductor, the design of composite photocatalyst containing BiVO4 with surpassing the recombination of photoinduced electron and hole is highly required. In this study, magnetic composite photocatalyst with NiFe2O4 and BiVO4 has developed through two-steps hydrothermal method. The results show that the morphology of the bare BiVO4 had a decahedral shape with smooth surfaces along with particles, while the morphology of the bare NiFeO4 had nanoparticles with the diameter in a range of 10-20 nm. In the case of 20% NiFe2O4/ BiVO4 samples, a large of nanoparticles were deposited into large bulk, implying the incorporation of NiFe2O4 nanoparticles on the surface of BiVO4 catalyst. Compared with the bare BiVO4, the NiFe2O4/BiVO4 composites had a higher photocatalytic efficiency for photodecomposition of rhodamine B (RhB) under visible LED light irradiation. The improvement of photocatalytic degradation RhB activity should be attributed to a direct Z‐scheme system. Therefore, the fabrication of semiconductors with a combination of magnetic materials provides new insight for the enhancement of their photocatalytic performance.

Sunlight Selective Photodeposition of CoOx(OH)y and NiOx(OH)y on Truncated Bipyramidal BiVO4 for Highly Efficient Photocatalysis.

Facet-engineered monoclinic scheelite BiVO4 particles decorated with various cocatalysts were successfully synthesized by selective sunlight photodeposition of metal or metal oxy(hydroxide) nanoparticles onto the facets of truncated bipyramidal BiVO4 monoclinic crystals coexposing {010} and {110} facets. X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning Auger microscopy revealed that metallic silver (Ag) and cobalt (oxy)hydroxide (CoOx(OH)y) particles were selectively deposited onto the {010} and {110} facets, respectively, regardless of the cocatalyst amount. By contrast, the nickel (oxy)hydroxide (NiOx(OH)y) photodeposition depends on the nickel precursor amount with an unprecedented selectivity for 0.1 wt % NiOx(OH)y/BiVO4 with a preferential deposition onto the {010} facets and the edges between the {110} facets. Moreover, these noble metal-free heterostructures led to remarkable photocatalytic properties for rhodamine B photodecomposition and sacrificial water oxidation reactions. For instance, 0.2 wt % CoOx(OH)y/BiVO4 led to one of the highest oxygen evolution rates, i.e., 1538 μmol h-1 g-1, ever described which is ten times higher than that found for bare BiVO4. The selective deposition of cobalt (oxy)hydroxide species onto the more electron-deficient facet of truncated bipyramidal monoclinic BiVO4 particles favors photogenerated charge carrier separation and therefore plays a key role for efficient photochemical oxygen evolution.

Fabrication of BiVO4-Ni/Co3O4 photoanode for enhanced photoelectrochemical water splitting

The low efficiency of charge separation and slow kinetics of water oxidation of BiVO4 limit its application in the PEC water splitting. Here, an effective strategy is explored with Ni-doped Co3O4 (Ni/Co3O4) decorated BiVO4 photoanode by a simple route. The photocurrent of the BiVO4-Ni/Co3O4 (2.23 mA/cm2 at 1.23 VRHE biases) has significantly increased up to 4.4 times of that of bare BiVO4, and the Vonset of BiVO4-Ni/Co3O4 shows a significant negative shift (180 mV) to 0.23 V. The IPCE value of BiVO4-Ni/Co3O4 (27%, 380 nm) is about 5 times that of the BiVO4 (5%). The ηinjection and ηseparation of BiVO4-Ni/Co3O4 at 1.23 VRHE reaches 75.82% and 37.08%. The results demonstrate that the Ni/Co3O4 could enhance the charge transfer and accelerate the kinetics of water oxidation reaction, leading to the excellent PEC water splitting performance of the photoelectrode.