Surface Of BiVO4 Research Articles

Synergistic effect of FeOOH cocatalyst and Al2O3 passivation layer on BiVO4 photoanode for enhanced photoelectrochemical water oxidation

BiVO4 is one of the most attractive photoanodes for water oxidation due to its 2.4 eV narrow band gap, suitable band edge position, good stability in aqueous solution, low cost and non-toxicity. However, due to some inherent disadvantages such as low carrier mobility, severe charge recombination and slow water oxidation kinetics, the actual BiVO4 photocurrent density is often lower than the theoretical value of 7.5 mA cm−2. In this paper, BiVO4 was modified by alkali-treated Al2O3 passivation layer and FeOOH, and the photocurrent density of BiVO4 reached an astonishing 3.8 mA cm−2 at 1.23 VRHE, and the ABPE (applied bias photon-to-current efficiency) was close to 1 %. The detailed structural characterization and electrochemical test show that Al2O3 prepared by ALD (atomic layer deposition) can play a role in passivation of BiVO4 surface state after alkali treatment, inhibit electron hole recombination on BiVO4 surface, and accelerate hole transfer. As a hole storage layer and catalyst layer, FeOOH promoted the interfacial hole transfer, increased the active sites at the electrode electrolyte interface, and significantly increased the water oxidation activity. This work provides a novel method to enhance the performance of water electrolysis by using ALD to assist passivation of bismuth vanadate photoanode surface states.

Enhanced water splitting on (010) facet-exposed BiVO4 photoanode with improved carrier injection efficiency

Transition metal oxide semiconductors, noted for their stability and suitable bandgap, are promising photoanodes for water splitting. Surface engineering is critical to tackle issues like low carrier mobility and charge recombination, stemming from atomic arrangement and Fermi level differences. While exposing dominant crystal facets boosts photocatalytic capability, it can hinder carrier injection into the electrolyte. In this study, BiVO4 films with various facet exposures were synthesized and characterized using scanning electron microscopy and x-ray diffraction to confirm their morphology and crystalline structure. Mott–Schottky analysis was employed to investigate changes in the band structure near the semiconductor–electrolyte interface, revealing that high (010)-BiVO4 facet exposure enhances carrier separation but reduces injection efficiency. The results from photoconductive atomic force microscopy tests demonstrated that enhanced band bending at the semiconductor interface improves hole transfer. Coating the (010)-BiVO4 photoanode with MoS2 and an amorphous ZrO2 interlayer yielded a photocurrent density of 0.6 mA cm−2 at 1.2 V (vs RHE) under AM 1.5 G illumination, tripling the pristine photoanode's performance and nearly tripling water splitting efficiency. Mechanism revealing the improved photoelectrochemical performance is attributed to a greater band bending on the BiVO4 surface, enhancing hole injection dynamics. This work provides a feasible strategy for a deeper understanding of the intrinsic mechanisms of facet engineering and improving the activity of photoanodes.

Hydroxyl-enriched hydrous tin dioxide-coated BiVO4 with boosted photocatalytic H2O2 production

The rapid decomposition of H2O2 on the surface of inorganic photocatalyst (BiVO4) and insufficient proton supply from water leads to a low photosynthetic yield of H2O2. Herein, hydrous tin dioxide (HSnO) with massive hydroxyl groups was coated on the BiVO4 surface to greatly improve the photocatalytic H2O2 activity via simultaneous realization of providing sufficient protons and inhibiting H2O2 decomposition. After the coating of HSnO, Au nanoparticles as the O2-reduction active sites were selectively deposited on the (010) facet of BiVO4 to synthesize the Au/BiVO4@HSnO photocatalyst. The resulting Au/BiVO4@HSnO photocatalyst exhibits excellent H2O2-production performance, in which the photogenerated H2O2 concentration (210.7 ​μmol ​L−1) is about 4.8 times higher than that of the Au/BiVO4 after 2 ​h light irradiation in pure water. The outstanding photocatalytic performance can be attributed to simultaneous enhancement of H2O2 generation and the suppression of H2O2 decomposition by HSnO coating. Specifically, the HSnO coating with massive hydroxyl groups provides enough protons to promote the catalytic transformation of O2 into H2O2 on Au nanoparticles. More importantly, the HSnO coating not only allows water macular to effectively permeate onto BiVO4 surface for rapid oxidation reaction, but also greatly inhibits the reverse reaction of H2O2 decomposition via decreasing its affinity with BiVO4 surface. This research offers new insights for boosting photocatalytic H2O2 production through surface coating strategy.

Photoelectrocatalytic CO2 Reduction to Formate Using a BiVO4/ZIF-8 Heterojunction.

Converting CO2 into high-value chemical fuels through green photoelectrocatalytic reaction path is considered as a potential strategy to solve energy and environmental problems. In this work, BiVO4/ZIF-8 heterojunctions are prepared by in-situ synthesis of ZIF-8 nanocrystals with unique pore structure on the surface of BiVO4. The experimental results show that the silkworm pupa-like BiVO4 is successfully combined with porous ZIF-8, and the introduction of ZIF-8 can provide more sites for CO2 capture. The optimal composite ratio of 4 : 1-BiVO4/ZIF-8 exhibits excellent CO2 reduction activity and the lowest electrochemical transport resistance. In the electrocatalytic system, the formate Faraday efficiency of 4 : 1-BiVO4/ZIF-8 at -1.0 V vs. RHE is 82.60 %. Furthermore, in the photoelectrocatalytic system, the Faraday efficiency increases to 91.24 % at -0.9 V vs. RHE, which is 10.8 times higher than the pristine BiVO4. The results show that photoelectric synergism can not only reduce energy consumption, but also improve the Faraday efficiency of formate. In addition, the current density did not decrease during 34 h electrolysis, showing long-term stability. This work highlights the importance of the construction of heterojunction to improve the performance of photoelectrocatalytic CO2 reduction.

Facet-Engineered BiVO4 Photocatalysts for Water Oxidation: Lifetime Gain Versus Energetic Loss.

A limiting factor to the efficiency of water Oxygen Evolution Reaction (OER) in metal oxide nanoparticle photocatalysts is the rapid recombination of holes and electrons. Facet-engineering can effectively improve charge separation and, consequently, OER efficiency. However, the kinetics behind this improvement remain poorly understood. This study utilizes photoinduced absorption spectroscopy to investigate the charge yield and kinetics in facet-engineered BiVO4 (F-BiVO4) compared to a non-faceted sample (NF-BiVO4) under operando conditions. A significant influence of preillumination on hole accumulation is observed, linked to the saturation and, thus, passivation of deep and inactive hole traps on the BiVO4 surface. In DI-water, F-BiVO4 shows a 10-fold increase in charge accumulation (∼5 mΔOD) compared to NF-BiVO4 (∼0.5 mΔOD), indicating improved charge separation and stabilization. With the addition of Fe(NO3)3, an efficient electron acceptor, F-BiVO4 demonstrates a 30-fold increase in the accumulation of long-lived holes (∼45 mΔOD), compared to NF-BiVO4 (∼1.5 mΔOD) and an increased half-time, from 2 to 10 s. Based on a simple kinetic model, this increase in hole accumulation suggests that facet-engineering causes at least a 50-100 meV increase in band bending in BiVO4 particles, thereby stabilizing surface holes. This energetic stabilization/loss results in a retardation of OER relative to NF-BiVO4. This slower catalysis is, however, offset by the observed increase in density and lifetime of photoaccumulated holes. Overall, this work quantifies how surface faceting can impact the kinetics of long-lived charge accumulation on metal oxide photocatalysts, highlighting the trade-off between lifetime gain and energetic loss critical to optimizing photocatalytic efficiency.

Strong evidence for interface-field-induced photocarrier separation in new AgFeO2-BiVO4 heterostructures and their efficient photo-Fenton degradation of ciprofoxacin

Deep elucidation of photocarrier transfer and separation mechanism is scientifically significant for developing new photocatalysts in pollutant elimination. In this study, we have immobilized AgFeO2 (AFO) nanoparticles on the surface of BiVO4 (BVO) nanobricks to construct new BVO-AFO heterostructured photocatalysts. Multiple advanced characterization techniques combined with theoretical calculations corroborate substantial evidence for the formation of built-in electric field at the BVO-AFO heterojunction interface and efficient photocarrier transfer/separation behavior and mechanism. Simulated-sunlight-driven photodegradation of ciprofoxacin (CIP) demonstrates an important enhanced photocatalysis of the heterostructure photocatalysts; particularly, the BVO-15 %AFO exhibits a photodegradation performance with η(30 min) = 89.9 % and kapp = 0.06659 min−1, which is enhanced by 4.2 (or 3.4) times over that of bare BVO (or AFO). The heterostructure-enhanced photocatalysis is benefited from the interface-field-facilitated transfer and separation of photocarriers, thus extending their lifetime and making them more probable to participate in the photocatalytic reactions. Furthermore, the BVO-AFO heterostructured photocatalysts demonstrate an important activation of peroxymonosulfate (PMS) or H2O2 to generate additional •OH and •SO4− reactive species, thus further promoting the CIP degradation. This work provides an important scientific basis for designing excellent heterostructured photocatalysts.

Surface-controlled oxygen vacancy-rich Bi/BiVO4 Schottky junction for highly selective and active photocatalytic nitrogen fixation

The modulation of active site density and localized electron concentration represents a crucial step in enhancing nitrogen activation, thereby significantly augmenting the efficiency of photocatalytic nitrogen fixation. In this paper, Bi/BiVO4 Schottky junctions enriched with oxygen vacancies (Bi/Vo-BVO) were fabricated by in situ reduction. Compared to BiVO4, Bi/Vo-BVO composites exhibited 8.4-fold enhancement in ammonia synthesis yield, reaching a maximum rate of 167.74 μmol·g−1·h−1. In situ FTIR spectroscopy and isotopic labeling experiments definitively demonstrated that the nitrogen constituent of NH4+ is derived from N2. N2-TPD and DFT calculation collectively suggest that the surface of Bi/Vo-BVO, enriched with ligand-unsaturated V4+ species, furnishes a substantial array of chemisorption sites for N2 molecules, attributed to the abundance of oxygen vacancies. In situ XPS coupled with DFT corroborate that the photoexcited electrons within the BiVO4 valence band accumulate in the conduction band, thereby directly facilitating the activation of N2 adsorbed at the V4+ active sites; The built-in electric field established at the interface between Bi and BiVO4 substantially facilitates the enrichment of Bi-emitted thermal electrons within oxygen vacancies on BiVO4 surface. These electrons subsequently migrate towards and interact with the adsorbed N2 via the V4+ active sites. The synergistic photothermal electrons activation mechanism of N2 not only enhances the efficiency of light energy utilization but maximizes the catalytic efficacy of the photocatalyst through the full exploitation of its intrinsic catalytic potential.

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.

In Situ Photoelectrochemical‐Induced Surface Reconstruction of BiVO4 Photoanodes for Solar Fuel Production

BiVO4 has been widely concerned due to its great potential in photoelectrochemical (PEC) water splitting. However, low carrier mobilities and high recombination efficiency of photogenerated carriers impede its photocatalytic performance. Herein, an in situ PEC cyclic‐voltammetry‐induced surface reconstruction of BiVO4 photoanodes (BVO pristine) is developed with significantly enhanced efficiency for solar water splitting. A series of in situ characterizations (including in situ X‐ray diffraction, in situ Raman), together with electrochemical tests and density‐functional theory calculations, reveal that during the photoelectrical activation process, the BVO pristine surfaces undergo a crystal plane reconstruction with greatly increased {040} crystal face to promote the separation of photogenerated carriers. In addition, abundant vanadium vacancies and oxygen vacancies are also introduced into the BiVO4 surface during the crystal face reconstruction process with more favorable surface water adsorption and increased injection efficiency of photogenerated carriers. Therefore, the charge‐transfer resistance (Rct) between BVO pristine and electrolyte under AM 1.5G illumination substantially reduced from the original 15 200 to 2820 Ω after the activation. Moreover, the photocurrent density of activated BVO pristines increases more than 12 times, relative to the original BiVO4. In this work, a new horizon for in situ photoelectric activation of semiconductor photoelectrodes with significantly enhanced PEC water splitting is provided.

Tethering Cobalt Ions to BiVO4 Surface via Robust Organic Bifunctional Linker for Efficient Photoelectrochemical Water Splitting.

In the quest for efficient and stable oxygen evolution catalysts (OECs) for photoelectrochemical water splitting, the surface modification of BiVO4 is a crucial step. In this study, a novel and robust OEC, based on 3-(bis(pyridin-2-ylmethyl) amino) propanoic acid bifunctional linker known as dipicolyl alanine acid (DPAA) and cobalt ions, is prepared and fully characterized. The DPAA is anchored to the surface of BiVO4 and utilized to tether cobalt ions. The Co-DPAA/BiVO4 photoanode exhibits remarkable stability and efficiency toward photoelectrochemical water oxidation. Specifically, it showed anodic photocurrent increase of 7.1, 5.0, 3.0, and 1.3-fold at 1.23VRHE as compared to pristine BiVO4, DPAA/BiVO4, Co-BiVO4, and Co-Pi/BiVO4 photoanodes, respectively. The photoelectrochemical and IMPS studies revealed that the Co-DPAA/BiVO4 photoanode exhibits a longer transient decay time for surface-trapped holes, higher charge transfer kinetics, and charge separation efficiency compared to Co-Pi/BiVO4 and pristine BiVO4 photoelectrodes. This indicates that the Co-DPAA effectively reduces surface recombination and facilitates charge transfer. Moreover, at 1.23VRHE, the Co-DPAA/BiVO4 photoanode achieved a faradic efficiency of 92% for oxygen evolution reaction and could retain a turnover frequency of 3.65s-1. The- exhibited effeciency is higher than most of the efficient molecular oxygen evolution catalyst based on Ru.

Nanoparticulated Vanadium Oxide on BiVO4 for Boosting Photoelectrochemical Glycerol Oxidation

Hydrogen (H2) has been spotlighted as ideal energy carrier due to its relatively higher energy density compared to fossil fuel and no carbon emissions during the energy generation. However, most of current produced H2 comes from as byproducts in fossil fuel reforming processes. To reduce dependence on fossil fuel in the H2 production process, photoelectrochemical (PEC) water splitting is considered as promising strategy for producing H2 using sustainable resources. Nevertheless, the insufficient efficiency in PEC water oxidation oxygen evolution reaction (OER) has limited overall PEC water splitting system efficiency due to its relatively high oxidation potential and sluggish catalytic kinetics. Furthermore, the low value of generated oxygen has been pointed out as obstacle from an economic perspective. To overcome these challenges, glycerol, byproduct of biodiesel, has been attracted numerous attentions as PEC oxidation resource since it has three hydroxyl groups and relatively lower oxidation potential than OER. Furthermore, glycerol oxygenated value-added products like dihydroxyacetone (DHA) can improve economics of PEC hydrogen production system. Upon these strengths, PEC glycerol oxidation reaction (GOR) provides improved strategy that generates value-added products in anodic part and green energy source (H2) in cathodic part simultaneously, which can replace PEC water splitting. Bismuth vanadate (BiVO4) is one of the most promising transition metal oxide based catalyst for PEC GOR due to its relatively narrow bandgap, high theoretical photocurrent density and deep positive valence band maximum (VBM) position. Additionally, although the surface kinetics of BiVO4 for OER has been sluggish, it potentially would be advantage for GOR with high production rate. However, the relatively instability of BiVO4 in acidic electrolyte during operation and lower selectivity of oxygenated products has hindered their practical application in PEC GOR. To solve these problems, introduction of nanoparticles as cocatalysts has been much studied for ameliorating surface kinetics and passivation the surface of photoanode. However, the interface between nanoparticles and photoanode with poor chemical interaction can induce the higher interfacial resistance and slow charge transfer efficiency rather. In this study, we present in-situ vanadium oxide (VOx) nanoparticle decoration on the surface of BiVO4 (VOx/BiVO4) via selective etching process using alkaline treatment for enhancing PEC GOR and we report the world best photocurrent density based on BiVO4 photoanode for GOR with high selective DHA production. VOx nanoparticles with an average size of 5 nm by selective etching process using alkaline treatment is decorated on the surface of BiVO4. The VOx promotes the surface reaction kinetics via modulating the fermi level and enhanced photovoltage of BiVO4 and improves long-term stability for GOR by compensation of V5+ and Bi3+, which combines both efficiency and stability. Furthermore, the surface decorated photoanode presents a 6.82 mA/cm2 (1.34-fold improvement) photocurrent density at 1.23 V versus the reversible hydrogen electrode (RHE) under 1 sun illumination, which has been attributed enhanced catalytic kinetics with upshifted fermi level and photovoltage of BiVO4. Moreover, the long-term stability of VOx/BiVO4 has been exhibited over 10 hours and the high selectivity for DHA is achieved. This study presents insight into the role vanadium of selective etched VOx on the surface of BiVO4 with low valence state than that of BiVO4 and improving the potential of BiVO4 based catalyst as GOR photoanode for high selective value-added DHA production using solar energy.

Oxidation of Ethylene Glycol into Valuable Chemical Using BiVO4 Photoanode

Introduction Plastic photoreforming using photocatalysts is a solar-powered technology that facilitates the generation of hydrogen (H2) from water while simultaneously breaking down plastic waste into valuable organic products. While the focus in the past few decades has predominantly centered on enhancing the H2 production efficiency, recent attention has shifted towards selective plastic oxidation reactions (U. Nwosu, et al. Renew. Sust. Energ. Rev. , 2021, 148, 111266). However, the investigation of effective cocatalysts for selective oxidation of plastic compounds has not been well studied.The photoelectrochemical (PEC) system offers a promising approach by segregating the anodic and cathodic processes, thereby enabling a more concentrated focus on the oxidation reaction in the design of reactions. In this study, we evaluate the BiVO4 photoanode modified with various cocatalysts, for example, cobalt phosphate (Co-Pi) for the oxidation of ethylene glycol (EG), a crucial component in the formation of polyethylene terephthalate (PET). Additionally, we introduce acetonitrile (MeCN) into the reactant mixture to suppress the oxygen evolution reaction (OER), which otherwise competes with the ethylene glycol oxidation reaction (EGOR), creating a more conducive reaction environment for enhanced efficiency. Materials and Methods The BiVO4 photoanode on fluorine doped tin oxide (FTO) glass was fabricated as previously reported (V. Andrei, et al. Adv. Energy Mater , 2018, 8, 1801403). Briefly,BiOI precursor was electrochemically deposited on the FTO glass and then drop-casted a vanadyl acetylacetonate [VO(acac)2] solution onto the surface and heated at 723 K for 60 min. The deposition of the Co-Pi cocatalyst onto BiVO4 was achieved by photoassisted electrodeposition method. The obtained photoanodes were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). PEC measurements were carried out using a three-electrode configuration under simulated solar irradiation (100 mW cm− 2, AM 1.5G). The experiments were performed in various solutions containing 1 M EG: 0.5 M Na2SO4 in H2O, 0.1 M NaClO4 in MeCN, and the mixed solution of MeCN and H2O. Product analysis was performed using proton nuclear magnetic resonance (1H NMR). Results and discussion According to the XRD and SEM results, the formation of nanoporous BiVO4 film on FTO glass was confirmed. To assess the PEC performance for EGOR using BiVO4 electrode, we carried out the experiments under conditions with and without the EG substrate (Figure (a)). With the addition of EG, a notable shift of the onset potential from 0.6 VRHE to 0.5 VRHE was observed. In addition, the photocurrent density at 1.2 VRHE increased from 0.67 mA/cm2 to 0.92 mA/cm2. This result indicates that EGOR is more favorable on the BiVO4 surface compared to OER. The Co-Pi cocatalyst deposition on the BiVO4 notably increased the current under both conditions, with and without the EG substrate. Although Co-Pi is commonly recognized for its catalytic role in OER, our experiment surprisingly revealed its positive impact on EG performance as well. The Co-Pi/BiVO4 photoanode exhibited a negative shift of the onset potential to 0.3 VRHE and an enhancement of photocurrent density to 2.04 mA/cm2 at 1.2 VRHE for EGOR compared to bare BiVO4. Additionally, the Co-Pi/BiVO4 photoanode showed 16.9% and 2.7% faradaic efficiencies (FE) for formate and glyoxal production, respectively, while bare BiVO4 exhibited 10.6% FE for formate and no glyoxal production.Under aqueous conditions, the FE for EGOR is currently low due to the competition between OER and EGOR. To overcome this challenge and enhance the EGOR efficiency, we introduced MeCN into the aqueous solution because MeCN has higher (more positive) anodic oxidation potential than the aqueous medium (L. M. Reid, et al. Sustainable Energy Fuels , 2018, 2, 1905-1927). In the MeCN-water mixed solution (MeCN:water = 9:1), OER was effectively suppressed to 0.33 mA/cm2, while EGOR was significantly enhanced to 2.50 mA/cm2 at 1.2 VRHE potential (Figure (b)). This MeCN-water mixed solvent created a more favorable environment for EGOR on bare BiVO4, resulting in a notable increase in FE for formate to 19.8% and FE for glyoxal to 13.2%, which represents a 1.87 and 4.89 times improvement, respectively, compared to the pure aqueous condition. Conclusions The deposition of Co-Pi cocatalyst on the BiVO4 film improved the photocurrent density and FE for formate production. Moreover, the introduction of MeCN in the solvent created a more favolable reaction condition for EGOR, suppressing OER and increasing the EGOR activity. Figure 1

Green light all the way: Triple modification synergistic modification effect to enhance the photoelectrochemical water oxidation performance of BiVO4 photoanode

The recombination of photogenerated electron-hole pairs of the photoanode seriously impairs the application of bismuth vanadate (BiVO4) in photoelectrochemical water splitting. To address this issue, we prepared a Yb:BiVO4/Co3O4/FeOOH composite photoanode by employing drop-casting and soaking methods to attach Co3O4/FeOOH cocatalysts to the surface of ytterbium-doped BiVO4. The prepared Yb:BiVO4/Co3O4/FeOOH photoanode demonstrates a high photocurrent density of 4.89 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (RHE), which is 5.1 times that of bare BiVO4 (0.95 mA cm−2). Detailed characterization and testing demonstrated that Yb doping narrows the band gap and significantly enhances the carrier density. Furthermore, Co3O4 serves as a hole transfer layer to expedite hole migration and diminish recombination, while FeOOH offers additional active sites and minimizes surface trap states, thus boosting stability. The synergistic effects of Yb doping and Co3O4/FeOOH cocatalyst significantly improved the reaction kinetics and overall performance of PEC water oxidation. This work provides a strategy for designing efficient photoanodes for PEC water oxidation.

Solar-driven highly selective conversion of glycerol to dihydroxyacetone using surface atom engineered BiVO4 photoanodes

Dihydroxyacetone is the most desired product in glycerol oxidation reaction because of its highest added value and large market demand among all possible oxidation products. However, selectively oxidative secondary hydroxyl groups of glycerol for highly efficient dihydroxyacetone production still poses a challenge. In this study, we engineer the surface of BiVO4 by introducing bismuth-rich domains and oxygen vacancies (Bi-rich BiVO4-x) to systematically modulate the surface adsorption of secondary hydroxyl groups and enhance photo-induced charge separation for photoelectrochemical glycerol oxidation into dihydroxyacetone conversion. As a result, the Bi-rich BiVO4-x increases the glycerol oxidation photocurrent density of BiVO4 from 1.42 to 4.26 mA cm−2 at 1.23 V vs. reversible hydrogen electrode under AM 1.5 G illumination, as well as the dihydroxyacetone selectivity from 54.0% to 80.3%, finally achieving a dihydroxyacetone production rate of 361.9 mmol m−2 h−1 that outperforms all reported values. The surface atom customization opens a way to regulate the solar-driven organic transformation pathway toward a carbon chain-balanced product.

BiVO4 photoanode modified with FeOOH cocatalyst for visible-light-driven photoelectrocatalytic degradation of organic pollutants

Photoelectrocatalytic (PEC) could effectively and gently treat wastewater. Nonetheless, catalysts face the pronounced tendency of sluggish photogenerated carrier transfer and carrier recombination. In this paper, we herein fabricate FeOOH/BiVO4 photoanode through the incorporation of a cocatalyst FeOOH onto the BiVO4 surface. This modified photoanode demonstrated improved performance when coupled with peroxomonosulfate (PMS) for the purpose of oxidizing tetracycline hydrochloride (TCH) within the PEC system. In the presence of 0.3 mM PMS, the degradation efficiency of TCH increased from 65 % to 88 % within 60 min. The effects of PMS concentration, applied voltage and TCH concentration on the decomposition were studied in detail. Through free radical scavenging experiments, it was found that SO4•-, h+ and ·OH played an important role in TCH degradation. In addition, the FeOOH/BiVO4 with PMS activation in the PEC system also could be capable of dealing with some more organic pollutants (antibiotics and dyes) and achieving good degradation effect. More importantly, TCH degradation rate by FeOOH/BiVO4 photoanode is still over 80 % after five cycles of reuse. This work provides a promising approach for the synthesis of novel photoanodes in the PEC systems with excellent PEC properties in removing environmental pollutants.

Surface plasmon enhancement of 1D Ag nanowires modified electro-treated BiVO4 photoanode with abundant oxygen vacancies for solar water oxidation

The high carrier complexation rate is still one of the main obstacles for bismuth vanadate (BiVO4) to be used in photoelectrochemical (PEC) water oxidation. In this work, we used a simple method for dropping one dimension (1D) silver nanowires (Ag NWs) on the surface of electro-treated BiVO4 (Ag NWs/E-BiVO4). The photocurrent of Ag NWs/E-BiVO4 under AM 1.5 G illumination reaches to 3.12 mA/cm2 which is about 6.2 times than the pure BiVO4 photoelectrode. Meanwhile, the photogenerated charges injection efficiency of Ag NWs/E-BiVO4 photoelectrodes increasing from 12.7 % to 77.5 % than the pure BiVO4 photoelectrode. This is because the surface plasmon resonance (SPR) effect of 1D Ag nanowires enhanced the visible light absorption and provide more Ag active sites. Furthermore, the density functional theory (DFT) calculations show that the Ag NWs/E-BiVO4 have the best adsorption capacity for OH– and the electro-treated BiVO4 with rich oxygen vacancies greatly improves the electron transport efficiency which is benefit for improving the PEC catalytic performance. Thus, this work provides a simple method to enhance the PEC water splitting performance of BiVO4.

Coating effect of metal organic complex (Co-DTPMP) layer on enhancing PEC water oxidation performance of BiVO4 photoanode

Photoelectrochemical (PEC) water splitting is a promising method for transforming solar energy into clean and sustainable energy. However, PEC is severely limited, and they cannot achieve the predicted photocurrent density owing to the severe photochemical deterioration of the electrode and the recombination of photogenerated carriers. In this study, BiVO4/Co-diethylenetriamine Penta (methylene phosphonic acid) (BVO/Co-DTPMP) co-catalyst was successfully prepared as a nanoporous photoanode. Diethylenetriamine Penta (methylene phosphonic acid) was crosslinked with Co ions and coated on the BiVO4 surface by successive ionic layer adsorption and reaction (SILAR) to reduce fast recombination, which correlated with the BiVO4 photoanode. Various characterization and PEC measurements were conducted, revealing that the co-catalyst thin layer enhanced the charge separation and electrons transfer which significantly affected on the PEC performance of BiVO4, and the current density by BVO/Co-DTPMP was 4 mA cm−2 at 1.23 V vs. RHE. Furthermore, the co-catalyst exhibited improved charge transport and long-term stability.

Modified successive ionic layer adsorption and reaction for interconnected bismuth vanadate nanograins: Highly active visible light harvesting photoanodes

A modified successive ionic layer adsorption and reaction (SILAR) method is developed for depositing interconnected bismuth vanadate (BiVO4) nanoparticles with improved visible light harvesting activity. Facile control of preparative parameters like deposition cycles, anionic precursor, pH and deposition temperature significantly altered BiVO4 surface morphology. BiVO4 thin films prepared with Na3VO4 anionic precursor show dispersed nanoparticles type morphology and that deposited with NaVO3 precursor displays 3D interconnected nanoparticles morphology. The BiVO4 photoanodes with 3D interconnected nanoparticles morphology exhibits an excellent photocurrent density of 5.19 mA cm−2 at 1.23 V vs. RHE with superior photostability and improved applied bias photon to current efficiency (ABPE) (1.50 %) compared to dispersed nanostructured BiVO4 photoanodes. The excellent photoelectrochemical (PEC) characteristics of BiVO4 photoanodes with 3D interconnected nanoparticle morphology can be ascribed to porous morphology, optimum thickness, narrow band gap energy and favorable electronic band structure for water splitting. The current study illustrates the usefulness of the modified SILAR approach for depositing 3D interconnected BiVO4 nanoparticle morphology in a single step that is superior and efficient to previously reported multistep processes.

Double oxygen evolution co-catalysts modified BiVO4 to boost photoelectrochemical water oxidation performance

Improving the kinetics of oxygen evolution is crucial for enhancing the performance of photoelectrochemical (PEC) water splitting. Herein, this study utilizes a chemical self-growth method to grow NiFe tannic acid complex (NFTA) and Co(OH)2 on the surface of BiVO4 photoanode (BiVO4/NFTA/Co). As a result, the synergistic effects of NFTA and Co(OH)2 layers promote the efficiency and stability of BiVO4 photoanode towards PEC water oxidation. The photocurrent density of the obtained BiVO4/NFTA/Co photoanode reaches 4.97 mA cm−2, which is significantly greater than those of BiVO4/NFTA (4.36 mA cm−2), BiVO4/Co (2.51 mA cm−2), BiVO4 (1.34 mA cm−2), respectively. Detailed analysis confirms that NFTA could provide an efficient way to hasten the transfer of photo-generated holes on the photoanode surface and diminish the surface charge transfer resistance. In other hand, Co(OH)2 could be served as a cocatalyst to accelerate charge transfer for efficient oxygen evolution reaction as well as a protective layer to maintain the long-term stability of NFTA on the surface of BiVO4 during water oxidation. Such double oxygen evolution co-catalysts decoration strategy paves an effective pathway to enhance the PEC water oxidation performance of BiVO4 photoanode.

Boosting photoelectrocatalytic oxygen evolution activity of BiVO4 photoanodes via caffeic acid bridged to NiFeOOH

Bismuth vanadate (BiVO4) is a promising n-type photoanode material for photoelectrochemical (PEC) water splitting. However, its activity is impeded by poor charge carrier transport and sluggish oxygen evolution kinetics. In this study, we reports a Fe doping and caffeic acid (CA)/NiFeOOH (NiFe) modification with BiVO4 photoanode (NiFe/CA/Fe-BiVO4) to enhance the PEC water oxidation performance and stability. The modified BiVO4 demonstrates significant advantages in promoting the PEC performance and stability. Specifically, Fe doping via in-situ electro-deposition results in smaller crystal sizes, larger specific surface areas, and more exposed active sites. Furthermore, co-catalyst NiFe connects with Fe-BiVO4 through CA bridge facilitates a more uniform self-assembly distribution of NiFe on BiVO4 surface. The NiFe/CA/Fe-BiVO4 exhibits an excellent photocurrent density of 6.2 mA/cm2 at 1.23 VRHEand demonstrates good stability at 0.8 VRHE. In addition, the composite photoanode shows a high applied bias photon-to-current efficiency (ABPE) value of 2.15% at 0.65 VRHE. EPR and in-situ FTIR confirm the generation of superoxide active species (O2- and ·O2-) during the PEC water oxidation reaction.