Enhancement of Solar‐Driven Photocatalytic Activity of BiOI Nanosheets through Predominant Exposed High Energy Facets and Vacancy Engineering

The increasing application of exposed high energy facet is an effective strategy to improve the photocatalytic performance of photocatalysts because the vacancies are beneficial to photocatalytic reaction. Vacancy dominates numerous distinct properties of semiconductor materials and thus plays a conclusive role in the photocatalysis applications. In this work, two kinds of BiOI nanomaterials with different vacancies are synthesized via a facile solvothermal method. The positron annihilation analysis shows that the thinner BiOI nanosheets possess larger‐sized vacancy than BiOI nanoplates. Thus, BiOI nanosheets show the enhanced separation efficiency of electron–hole pairs and adsorption ability for contaminants under visible light. The results are also validated with the first‐principle computation. Therefore, higher photocatalytic activity to the photodegradation of tetracycline is observed from the nanosheets than that obtained from BiOI nanoplates. This work not only arouses attention to vacancies, but also opens up an avenue for precision design of vacancies to prepare novel photocatalytic materials driven under solar light.     

Oxygen‐Vacancy‐Introduced BaSnO3−δ Photoanodes with Tunable Band Structures for Efficient Solar‐Driven Water Splitting

To achieve excellent photoelectrochemical water‐splitting activity, photoanode materials with high light absorption and good charge‐separation efficiency are essential. One effective strategy for the production of materials satisfying these requirements is to adjust their band structure and corresponding bandgap energy by introducing oxygen vacancies. A simple chemical reduction method that can systematically generate oxygen vacancies in barium stannate (BaSnO₃ (BSO)) crystal is introduced, which thus allows for precise control of the bandgap energy. A BSO photoanode with optimum oxygen‐vacancy concentration (8.7%) exhibits high light‐absorption and good charge‐separation capabilities. After deposition of FeOOH/NiOOH oxygen evolution cocatalysts on its surface, this photoanode shows a remarkable photocurrent density of 7.32 mA cm^?2 at a potential of 1.23 V versus a reversible hydrogen electrode under AM1.5G simulated sunlight. Moreover, a tandem device constructed with a perovskite solar cell exhibits an operating photocurrent density of 6.84 mA cm^?2 and stable gas production with an average solar‐to‐hydrogen conversion efficiency of 7.92% for 100 h, thus functioning as an outstanding unbiased water‐splitting system.     

In Situ Formation of Oxygen Vacancies Achieving Near-Complete Charge Separation in Planar BiVO4 Photoanodes

Despite a suitable bandgap of bismuth vanadate (BiVO₄) for visible light absorption, most of the photogenerated holes in BiVO₄ photoanodes are vanished before reaching the surfaces for oxygen evolution reaction due to the poor charge separation efficiency in the bulk. Herein, a new sulfur oxidation strategy is developed to prepare planar BiVO₄ photoanodes with in situ formed oxygen vacancies, which increases the majority charge carrier density and photovoltage, leading to a record charge separation efficiency of 98.2% among the reported BiVO₄ photoanodes. Upon loading NiFeO_x as an oxygen evolution cocatalyst, a stable photocurrent density of 5.54 mA cm⁻² is achieved at 1.23 V versus the reversible hydrogen electrode (RHE) under AM 1.5 G illumination. Remarkably, a dual-photoanode configuration further enhances the photocurrent density up to 6.24 mA cm⁻², achieving an excellent applied bias photon-to-current efficiency of 2.76%. This work demonstrates a simple thermal treatment approach to generate oxygen vacancies for the design of efficient planar photoanodes for solar hydrogen production.     

New BiVO4 Dual Photoanodes with Enriched Oxygen Vacancies for Efficient Solar‐Driven Water Splitting

Bismuth vanadate (BiVO₄) is a promising photoanode material for photoelectrochemical (PEC) water splitting. However, owing to the short carrier diffusion length, the trade‐off between sufficient light absorption and efficient charge separation often leads to poor PEC performance. Herein, a new electrodeposition process is developed to prepare bismuth oxide precursor films, which can be converted to transparent BiVO₄ films with well‐controlled oxygen vacancies via a mild thermal treatment process. The optimized BiVO₄ film exhibits an excellent back illumination charge separation efficiency mainly due to the presence of enriched oxygen vacancies which act as shallow donors. By loading FeOOH/NiOOH as the cocatalysts, the BiVO₄ dual photoanodes exhibit a remarkable and highly stable photocurrent density of 5.87 mA cm^?2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination. An artificial leaf composed of the BiVO₄/FeOOH/NiOOH dual photoanodes and a single sealed perovskite solar cell delivers a solar‐to‐hydrogen conversion efficiency as high as 6.5% for unbiased water splitting.     

Designing a Transparent CdIn2S4/In2S3 Bulk-Heterojunction Photoanode Integrated with a Perovskite Solar Cell for Unbiased Water Splitting

The integration of photoelectrochemical photoanodes and solar cells to build an unbiased solar-to-hydrogen (STH) conversion system provides a promising way to solve the energy crisis. The key point is to develop highly transparent photoanodes, while its bulk separation efficiency (η_sep.) and surface injection efficiency are as high as possible. To resolve this contradiction, first a novel CdIn₂S₄/In₂S₃ bulk heterojunctions in the interior of nanosheets is designed as a photoanode with high transparency and an ultrahigh η_sep. up to 90%. Furthermore, decorating the ultrathin amorphous SnO₂ layer by atomic layer deposition, the surface oxygen-evolution kinetics of the photoanode are increased significantly. As a result, the onset potential of the photoanode shifts negatively to 0.02 V vs RHE, and the photocurrent density boosts to 2.98 mA cm⁻² at 1.23 V vs RHE, which is ten times higher than that of pristine CdIn₂S₄. Such a high-performance photoanode enables the integrated metal sulfide photoanode–perovskite solar cell system to deliver a STH conversion efficiency of 3.3%.     

Enhancement of Photocatalytic Activity of Bi2O3–BiOI Composite Nanosheets through Vacancy Engineering

Vacancy engineering is an effective strategy to enhance solar‐driven photocatalytic performance of semiconductors. It is highly desirable to improve the photocatalytic performance of composite nanomaterials by the introduction of vacancies, but the role of vacancies and the heterostructure in the photocatalytic process is elusive to the composite nanomaterials. Herein, the introduction of I vacancies can significantly enhance the photocatalytic activity of Bi₂O₃–BiOI composite nanosheets in a synergistic manner. The excellent photocatalytic performance of the Bi₂O₃–BiOI composites is attributed to the combination of Bi₂O₃ and BiOI and the existence of I vacancies in Bi₂O₃–BiOI composites. Specifically, density functional theory calculation shows that the existence of I vacancies would create a new electric states vacancy band below the conduction band of BiOI and thus can reduce the bandgap of BiOI nanosheets. This greatly facilitates the scavenging of the photogenerated electron on the surface of BiOI by Bi₂O₃, therefore, enhancing the overall photocatalytic activity of the composites. The enhanced photocatalytic efficiency is demonstrated by the degradation of tetracycline (TC), which reaches 96% after 180 min and by the high total organic carbon (TOC) removal (89% after 10 h visible light irradiation). This study provides a novel approach for the design of high‐performance composite catalysts.     

Plasmonic Enhancement in BiVO4 Photonic Crystals for Efficient Water Splitting

Photo‐electrochemical water splitting is a very promising and environmentally friendly route for the conversion of solar energy into hydrogen. However, the solar‐to‐H₂ conversion efficiency is still very low due to rapid bulk recombination of charge carriers. Here, a photonic nano‐architecture is developed to improve charge carrier generation and separation by manipulating and confining light absorption in a visible‐light‐active photoanode constructed from BiVO₄ photonic crystal and plasmonic nanostructures. Synergistic effects of photonic crystal stop bands and plasmonic absorption are observed to operate in this photonic nanostructure. Within the scaffold of an inverse opal photonic crystal, the surface plasmon resonance is significantly enhanced by the photonic Bragg resonance. Nanophotonic photoanodes show AM 1.5 photocurrent densities of 3.1 ± 0.1 mA cm^?2 at 1.23 V versus RHE, which is among the highest for oxide‐based photoanodes and over 4 times higher than the unstructured planar photoanode.     

Structural Engineering of BiVO4/CoFe MOF Heterostructures Boosting Charge Transfer for Efficient Photoelectrochemical Water Splitting

Boosting charge separation and transfer of photoanodes is crucial for providing high viability of photoelectrochemical hydrogen (H₂) generation. Here, a structural engineering strategy is designed and synthesized for uniformly coating an ultrathin CoFe bimetal-organic framework (CoFe MOF) layer over a BiVO₄ photoanode for boosted charge separation and transfer. The photocurrent density of the optimized BiVO₄/CoFe MOF(NA) photoanode reaches a value of 3.92 mA cm⁻² at 1.23 V versus reversible hydrogen electrode (RHE), up to 6.03 times that of pristine BiVO₄, due to the greatly increased efficiency of charge transfer and separation. In addition, this photoanode records one onset potential that is considerably shifted negatively when compared to BiVO₄. Transient absorption spectroscopy reveals that the CoFe MOF(NA) prolongs charge recombination lifetime by blocking the hole-transfer pathway from the BiVO₄ to its surface trap states. This work sheds light on boosting charge separation and transfer through structural engineering to enhance the photocurrent of photoanodes for solar H₂ production.     

0D/2D Z-scheme heterojunctions of g-C3N4 quantum dots/ZnO nanosheets as a highly efficient visible-light photocatalyst

Constructing Z-scheme heterojunctions comprising of constituents with different dimensionality is an effective strategy to spatially separate electron and hole. To fully utilize the synergistic coupling effect of dimensionality, herein, we first immobilize g-C₃N₄ quantum dots (CNQDs) onto ZnO nanosheets with oxygen vacancies (OV-ZnO) to create a 0D/2D hybrid via a facile and cost-effective approach. The CNQDs/OV-ZnO heterojunctions display CNQDs content-dependent performance in visible-light photocatalytic activity. The optimal CNQDs/OV-ZnO heterojunction exhibits high photocatalytic activity for degradation of methyl blue and bisphenol A, where the kinetic constant is 11.4 and 32.5 fold of pure OV-ZnO, respectively. Photoluminescence, electrochemical impedance spectroscopy and photocurrent verify that the photogenerated electron-hole pairs in this 0D/2D Z-scheme heterojunction have been effectively separated. The enhanced photocatalytic activity could be attributed to the synergistic effect of efficient Z-scheme charge separation, highly dispersed 0D CNQDs, coordinating sites of 2D OV-ZnO nanosheets and the strong coupling between them. In addition, the 3D flower-like structure constructed by 2D nanosheets greatly inhibits the leaching and loss of the photocatalyst in the recycling process, and ensures the high recycling ability of CNQDs/OV-ZnO. This work paves the way toward designing novel visible-light 0D/2D photocatalysts in the application of solar energy.     

Preparation of Au-BiVO4 heterogeneous nanostructures as highly efficient visible-light photocatalysts

Au-BiVO(4) heterogeneous nanostructures have been successfully prepared through in situ growth of gold nanoparticles on BiVO(4) microtubes and nanosheets via a cysteine-linking strategy. The experimental results reveal that these Au-BiVO(4) heterogeneous nanostructures exhibit much higher visible-light photocatalytic activities than the individual BiVO(4) microtubes and nanosheets for both dye degradation and water oxidation. The enhanced photocatalytic efficiencies are attributed to the charge transfer from BiVO(4) to the attached gold nanoparticles as well as their surface plasmon resonance (SPR) absorption. These new heteronanostructures are expected to show considerable potential applications in solar-driven wastewater treatment and water splitting.     

p-n异质结BiVO4/g-C3N4光阳极的制备及其光电化学水解性能

钒酸铋(BVO)可用于光电化学(PEC)水解产氢,但受限于其缓慢的表面水氧化动力学,在电极表面修饰单一的析氧助催化剂达不到理想的性能。本工作在BVO电极表面修饰FeNiO_x助催化剂可以显著降低起始电压,增强光电化学性能。此外,沉积g-C₃N₄后修饰FeNiO_x助催化剂得到的光电极具有更优异的性能。厚度适合的g-C₃N₄纳米片与BVO构成Ⅱ型p-n异质结,有效抑制了光生电子空穴的复合,促进了电极的电荷分离。电化学测试结果表明,沉积了g-C₃N₄后,电极的电荷分离效率达到88.2%,比BVO/FeNiO_x (60.6%)提升了近1.5倍。经过g-C₃N₄和FeNiO_x协同修饰的BVO/g-C₃N₄/Fe Ni O_x电极,表面电荷注入效率达到了90.2%,同时,在1....     

Nanostructured WO3/BiVO4 Photoanodes for Efficient Photoelectrochemical Water Splitting

Nanostructured photoanodes based on well‐separated and vertically oriented WO₃ nanorods capped with extremely thin BiVO₄ absorber layers are fabricated by the combination of Glancing Angle Deposition and normal physical sputtering techniques. The optimized WO₃‐NRs/BiVO₄ photoanode modified with Co‐Pi oxygen evolution co‐catalyst shows remarkably stable photocurrents of 3.2 and 5.1 mA/cm² at 1.23 V versus a reversible hydrogen electrode in a stable Na₂SO₄ electrolyte under simulated solar light at the standard 1 Sun and concentrated 2 Suns illumination, respectively. The photocurrent enhancement is attributed to the faster charge separation in the electronically thin BiVO₄ layer and significantly reduced charge recombination. The enhanced light trapping in the nanostructured WO₃‐NRs/BiVO₄ photoanode effectively increases the optical thickness of the BiVO₄ layer and results in efficient absorption of the incident light.     

3D Brochosomes‐Like TiO2/WO3/BiVO4 Arrays as Photoanode for Photoelectrochemical Hydrogen Production

An ideal photoelectrochemical (PEC) anode should process effective light absorption, charge transport, and separation efficiency. Here, a novel 3D brochosomes‐like TiO₂/WO₃/BiVO₄ array as an efficient photoanode by combining a colloid polystyrene sphere template and electrochemical deposition routes for PEC hydrogen generation is reported. The as‐fabricated 3D TiO₂/WO₃/BiVO₄ brochosomes photoanode yields excellent PEC performance with photocurrent densities of ≈3.13 and ≈4.27 mA cm^?2 with FeOOH/NiOOH catalyst, respectively, measured in 0.5 m Na₂SO₄ solution with 0.1 m Na₂SO₃ at 1.23 V versus reversible hydrogen electrode (RHE) under simulated AM1.5 light illumination, which is ≈6 times the reference sample of a planar WO₃/BiVO₄ film electrode. The significantly improved performance could be benefited from the ordered hollow porous structure that provides enhanced light absorption and efficient charge transport as well as improved charge separation efficiency by WO₃/BiVO₄ “host–guest” heterojunctions.     

Enhanced removal of organic pollutant by separable and recyclable rGH-PANI/BiOI photocatalyst via the synergism of adsorption and photocatalytic degradation under visible light

A novel three-dimension separable and recyclable rGH-PANI/BiOI photocatalyst with the synergism of adsorption-enrichment and photocatalytic-degradation was successfully prepared via a facile three-step hydrothermal method.The three-dimension reduced graphene oxide hydrogel(rGH)in with flower-like BiOI photocatalyst uniformly distributed not only possesses excellent adsorption and electron transport properties,but also is easy to be separated from water for recycling.In addition,polyphenylamine(PANI)provides superior hole transport ability due to its delocalized π-π conjugate structure.The cooperation of rGH and PANI greatly enhances the separation efficiency of photogenerated carriers,and finally improves the photocatalytic degradation behaviors.The removal rates of Rhodamine B(RhB)by rGH-PANI/BiOI-70％composite under visible light respectively reach 100％and 50.13％in static and dynamic systems,which are 12.85 and 3.58 times of BiOI,respectively.The removal rate does not show decrease after 5 recycles indicating the excellent separable and recyclable property of rGH-PANI/BiOI photocatalyst.The work provides an essential reference for designing and constructing hydrogel-based ternary composite photocatalysts with excellent synergism of adsorption and photocatalysis,which shows great potential in the treatment of water pollution.     

Full-spectrum responsive photocatalytic activity via non-noble metal Bi decorated mulberry-like BiVO4

Due to its appropriate bandgap(～2.4 eV)and efficient light absorption,bismuth vanadate(BiVO4)shows promising photocatalysis activity.However,the charge carrier recombination and poorelectron transmis-sion often induce poor photocatalytic performance.Herein,we report a new method to in-situ synthesize non-noble metal Bi decorated mulberry-like BiVO4 by a two-step calcination process.Comprehensive characterizations reveal that non-noble metal Bi nanoparticles grown in-situ on BiVO4 result in the red-shift of the absorbance edge,greatly extending the light absorption from the ultraviolet into the near-infrared region.The surface plasmon resonance excitation of Bi nanoparticles and synergetic effects between Bi and BiVO4 effectively improve the photocatalytic efficiency and promote the separation of photoinduced electron-hole pairs in mulberry-like BiVO4.Density functional theory(DFT)calculation results further verify that the electrons are transferred from Bi to BiVO4 and the formation of·OH radical in Bi/BiVO4 is attributed to the lower simulated free energy,which supports our experimental outcomes.This work provides a novel strategy to enhance light absorption and promote efficient solar utilization of photocatalysts for practical applications.     

氧空位超薄Co2AlO4纳米片的合成及其增强电催化氧析出反应（英文）

本文报道了通过脱合金和后续退火工艺合成一种新型超薄二维尖晶石结构的Co2Al O4纳米片.通过温和的溶剂热还原法将氧空位缺陷引入Co2Al O4纳米片中,使得电化学表面积增大,活性位密度变高,钴原子得到电子而产生更多的空轨道.这些空轨道有利于接受水分子中氧原子的孤对电子,促进水分子的活化.含有氧空位的超薄Co2Al O4纳米片在10 m A cm^-2时的过电位为280 m V,塔菲尔斜率为70.98 m V dec^-1.此外,其在碱性溶液中也表现出显著的稳定性,并且优于多数已报道的Co3O4电催化剂.该工作为制备高效的可持续新能源材料提供了新思路.     

Synergetic effects of Bi5+ and oxygen vacancies in Bismuth(Ⅴ)-rich Bi4O7 nanosheets for enhanced near-infrared light driven photocatalysis

The appropriate energy level position of photocatalysts dominates the photocatalytic redox reaction and utilization efficiency of solar energy for wastewater treatment.Herein,we report a near-infrared(NIR)light driven Bi5+-rich Bi4O7 photocatalyst,achieving a greatly enhanced photocatalytic activity for pollutant removal compared with Bi3+-replenished Bi2O3.Density functional theory calculations show the formation of an intermediate band in the Bi4O7 structure because of the hybridization of O 2p and Bi 4s orbits.The formation of the intermediate band not only narrows the band gap but also improves the optical absorption property and separation efficiency of the photoinduced carriers.The existence of the oxygen vacancies(OVs)in the Bi4O7 nanosheets ensures high carriers'concentration,which is verified by the Hall effect test.The synergetic effects of the OVs and Bi5+greatly accelerate the separation efficiency of the photogenerated carriers.Consequently,the Bi4O7 nanosheets exhibit enhanced NIR light driven photocatalytic activity for the degradation of rhodamine B and ciprofloxacin compared with the bulk Bi2O3.This study paves the way to the design of highly efficient NIR light-responsive Bi-based photocatalysts for environmental purification.     

Spinel Structural Disorder Influences Solar‐Water‐Splitting Performance of ZnFe2O4 Nanorod Photoanodes

Zinc spinel ferrite, ZnFe₂O₄ (ZFO), is an emerging photoanode material for photoelectrochemical (PEC) solar fuel production. However, a lack of fundamental insight into the factors limiting the photocurrent has prevented substantial advance in its performance. Herein, it is found that ZFO nanorod array photoelectrodes with varying crystallinity exhibit vastly different PEC properties. Using a sacrificial hole scavenger (H₂O₂), spatially defined carrier generation, and electrochemical impedance spectroscopy, it is shown that ZFO with a relatively poor crystallinity but a higher spinel inversion degree (due to cation disorder) exhibits superior photogenerated charge separation efficiency and improved majority charge carrier transport compared to ZFO with higher crystallinity and a lower inversion degree. Conversely, the latter condition leads to better charge injection efficiency. Optimization of these factors, and the addition of a nickel–iron oxide cocatalyst overlayer, leads to a new benchmark solar photocurrent for ZFO of 1.0 mA cm^?2 at 1.23 V versus reversible hydrogen electrode (RHE) and 1.7 mA cm^?2 at 1.6 V versus RHE. Importantly, the observed correlation between the cation disorder and the PEC performance represents a new insight into the factors important to the PEC performance of the spinel ferrites and suggests a path to further improvement.     

Mesocrystalline TiO<Subscript>2</Subscript> nanosheet arrays with exposed {001} facets: Synthesis via topotactic transformation and applications in dye-sensitized solar cells

A facile,fluorine-free approach for synthesizing vertically aligned arrays of mesocrystalline anatase TiO2 nanosheets with highly exposed {001} facets was developed through topotactic transformation.Unique mesocrystalline {001}-faceted TiO2 nanosheet arrays vertically aligned on conductive fluorine-doped tin oxide glass were realized through topotactic conversion from single-crystalline precursor nanosheet arrays based on lattice matching between the precursor and the anatase crystals.The morphology and microstructure of the {001}-faceted TiO2 nanosheets could be readily modulated by changing the reactant concentration and annealing temperature.Owing to enhanced dye adsorption,reduced charge recombination,and enhanced light scattering arising from the exposed {001} facets,in addition to the advantageous features of low-dimensional structure arrays (e.g.,fast electron transport and efficient charge collection),the obtained TiO2 nanosheet arrays exhibited superior performance when they were used as anodes for dye-sensitized solar cells (DSSCs).Particularly,{001}-faceted TiO2 nanosheet arrays ～15 μm long annealed at 500 ℃ showed a power conversion efficiency of 7.51％.Furthermore,a remarkable efficiency of 8.85％ was achieved for a DSSC based on double-layered TiO2 nanosheet arrays ～35 μm long,which were prepared by conversion from the precursor nanoarrays produced via secondary hydrothermal growth.     

Surface Self-Transforming FeTi-LDH Overlayer in Fe2O3/Fe2TiO5 Photoanode for Improved Water Oxidation

Integrating hematite nanostructures with efficient layer double hydroxides (LDHs) is highly desirable to improve the photoelectrochemical (PEC) water oxidation performance. Here, an innovative and facile strategy is developed to fabricate the FeTi-LDH overlayer decorated Fe₂O₃/Fe₂TiO₅ photoanode via a surface self-transformation induced by the co-treatment of hydrazine and NaOH at room temperature. Electrochemical measurements find that this favorable structure can not only facilitate the charge transfer/separation at the electrode/electrolyte interface but also accelerate the surface water oxidation kinetics. Consequently, the as-obtained Fe₂O₃/Fe₂TiO₅/LDH photoanode exhibits a remarkably increased photocurrent density of 3.54 mA cm⁻² at 1.23 V versus reversible hydrogen electrode (RHE) accompanied by an obvious cathodic shift (≈140 mV) in the onset potential. This work opens up a new and effective pathway for the design of high-performance hematite photoanodes toward efficient PEC water oxidation.