Fluorine-doped Tin Oxide Glass Research Articles

Decoration of PdAg Dual-Metallic Alloy Nanoparticles on Z-Scheme α-Fe2O3/CdS for Manipulable Products via Photocatalytic Reduction of Carbon Dioxide

Metal nanoparticles have been extensively used as co-catalysts in photocatalytic systems in order to pursue improvements in both reaction kinetics and selectivity. In this work, PdAg dual-metallic nanoparticles synthesized by the co-reduction method were decorated on a well-established α-Fe2O3/CdS Z-scheme photoactive material as a co-catalyst to study their performance for promoting the photoreduction of CO2. Herein, α-Fe2O3 and CdS were in situ synthesized on fluorine-doped tin oxide (FTO) glass by hydrothermal and SILAR (successive ionic layer adsorption and reaction) methods, respectively. The direct Z-scheme charge transfer path between Fe2O3 and CdS and the effective electron migration toward the PdAg mainly contributed to the excellent photocatalytic CO2 reduction performance. The controllable work function based on Pd (5.12) and Ag (4.26) constructed an appropriate band alignment with α-Fe2O3/CdS and displayed favorable production for CH4 rather than CO. The optimum ratio of PdAg 1:2 performed a 48% enhancement than pure Pd for photoreduction of CO2. Meanwhile, the enhanced charge separation improved the photoelectrochemical performance and photocurrent generation, and reduced the electrical resistance between components. This work provided insights into the dual-metallic co-catalyst for boosting the activity and selectivity of photocatalytic CO2 reduction.

Formation and crystallization of TiO2 nanostructures on various surfaces

A comparative study of the synthesis of TiO2 nanorods on fluorine-doped tin oxide (FTO) glass, Si, SiO2, Si/Ta, Si/TiN, Si/TiN/Ti and Si/HFO2 substrates by hydrothermal reaction is presented. Detailed analysis on the growth of TiO2 on pre-annealed Si/TiN/Ti and HfO2 (HFO) surfaces is also given. For Si/TiN/Ti, a pre-annealing procedure led to the transformation of Ti to a TiO2 layer which acts as a seed for aligned growth of TiO2 nanorods. In contrast, Si/HFO does not provide a nucleation site for the formation of aligned nanorods. Various samples were prepared by varying the synthesis conditions, i.e. pre- and post-annealing temperatures and hydrothermal reaction time to figure out the optimum conditions which lead to unidirectional and highly aligned nanorods. X-ray diffraction, scanning electron microscopy, ultraviolet–visible spectroscopy and Raman spectroscopy were used to study structural, morphological and optical properties of synthesized samples. It is found that TiO2 nanorods exhibit a rutile phase on the Si/Ti/TiN and Si/HFO substrates, but highly oriented vertical growth of nanorods has been observed only on pre-annealed Si/TiN/Ti substrates. On the other hand, TiO2 nanorods form dandelion-like structures on Si/HFO substrates. Growth of vertically oriented TiO2 nanorods on Si/TiN/Ti is attributed to the TiO2 seed layer which forms after the process of pre-annealing of substrates at a suitable temperature. Variation in hydrothermal reaction time and post-annealing temperature brings further improvement in crystallinity and morphology of nanorods. This work shows that the pre-annealed Si/TiN/Ti substrate is the optimal choice to achieve vertically oriented, highly aligned TiO2 nanorods.

Thin Films (FTO/BaTiO3/AgNPs) for Enhanced Piezo-Photocatalytic Degradation of Methylene Blue and Ciprofloxacin in Wastewater.

In this study, we investigate the ability of barium titanate/silver nanoparticles (BaTiO3/AgNPs) composites deposited on a fluorine-doped tin oxide (FTO) glass using tape-casting method to produce piezoelectric thin film (FTO/BaTiO3/AgNPs) for piezocatalytic, photocatalytic, and piezo-photocatalytic degradation of methylene blue (MB) and ciprofloxacin (CIP) in wastewater. The prepared piezoelectric materials (BaTiO3 and BaTiO3/AgNPs) were characterized using XRD, SEM, TEM, EDS, UV-DRS, TGA, PL, BET, EIS, and chronoamperometry. The UV-DRS showed the surface plasmon resonance (SPR) of Ag nanoparticles on the surface of BaTiO3 at a wavelength of 505 nm. The TEM images revealed the average Ag nanoparticle size deposited on the surface of BaTiO3 to be in the range of 10–15 nm. The chronoamperometry showed that the photoreduction of silver nanoparticles (AgNPs) onto BaTiO3 (BTO) resulted in a piezo-electrochemical current enhancement from 0.24 to 0.38 mA. The composites (FTO/BaTiO3/AgNPs) achieved a higher degradation of MB and CIP when the photocatalysis and piezocatalysis processes were merged. Under both ultrasonic vibration and UV light exposure, FTO/BTO/AgNPs degraded about 72 and 98% of CIP and MB from wastewater, respectively. These piezoelectric thin films were shown to be efficient and reusable even after five cycles, suggesting that they are highly stable. Furthermore, the reactive oxygen species studies demonstrated that hydroxyl radicals (·OH) were the most effective species during degradation of MB, with minor superoxide radicals (·O2–) and holes (h+). From this study, we were able to show that these materials can be used as multifunctional materials as they were able to degrade both the dye and pharmaceutical pollutants. Moreover, they were more efficient through the piezo-photocatalytic process.

Effect of temperature on the polymorphs of titania (TiO2) developed by sol-gel and hydrothermal processes for thin film uses

Titanium dioxide (TiO2) has been utilized for photovoltaic devices mostly as electron selective ply. Most of the transition metal complexes like TiO2 possess wider band gap to predominant relying on morphology of nano-particles. Most of the metal oxides possess excellent ability of harvesting extensive part of sunlight. This study reports, synthesis of TiO2 by using two different techniques i.e., sol-gel and hydrothermal. Later nano films was applied on fluorine doped tin oxide glass through spin coating at ambient temperature. Particles of TiO2 were synthesized at different temperatures however rest of the variable like solvent, concentration and amount of precursor were static. Nanoparticles of anatase titania synthesized through sol-gel had higher crystallinity. Particle size of synthesized particles was 12.2 nm at 25o C. Subsequently particles produced through hydrothermal procedure were large with an average particle size of 16 nm at 100o C. FTIR further confirmed the synthesis of anatase titania at 400-800 cm-1. X-ray diffraction technique also confirmed the synthesis of titania at 25.3o ,38.0o, 47o, 54.5o, 62.7o and 78o . UV-visible spectroscopy was performed to analyze optical properties exhibiting peak absorbance at 424 nm. This synthesized TiO2 anatase is extensively used for photovoltaic application.

Influence of the pH of anthocyanins on the efficiency of dye sensitized solar cells

The influence of the pH of anthocyanins on photovoltaic performance in dye-sensitized solar cells has been investigated. Anthocyanins were extracted from crushed leaf stocks of Manihot esculenta Crantz (Cassava plant) using methanol acidified with 0.5% trifluoracetic acid. The filtrate was concentrated using a rotary evaporator and partitioned against ethyl acetate. The anode was prepared by screen printing TiO2 paste on a previously cleaned fluorine-doped tin oxide (FTO) glass substrate. The cathode was made by applying plastisol on a previously cleaned FTO glass substrate using an artistic brush and later annealed at 450 °C for 20 min to activate platinum. The performance of the solar cells was measured using a solar simulator fitted with an AM1.5 air filter. Electron transport was studied using electrochemical impedance spectroscopy (EIS). It was observed that the short circuit current and efficiency dropped from pH 2 to pH 6 and peaked at pH 8, with values of 0.399 mA and 0.390%, respectively. It then drops further as the basicity increases. The open circuit voltage was observed to increase consistently from pH 2 to pH 12. EIS results showed that the electron density in the conduction band of TiO2 increases from pH 2 to pH 10 and drops from pH 10 to pH 12. It was concluded that, while a large number of electrons (∼1016m−3) are injected into the conduction band of TiO2, the majority do not contribute to the current but instead recombine with other electron acceptor species in the solar cell. However, the injected electrons cause an upwards shift in the quasi-Fermi level of electrons in the conduction band of TiO2. This explains the large variation in the open circuit voltage compared to the short circuit current.

Preparation of Photo-Bioelectrochemical Cells With the RC-LH Complex From Roseiflexus castenholzii.

Roseiflexus castenholzii is an ancient green non-sulfur bacteria that absorbs the solar energy through bacteriochlorophylls (BChls) bound in the only light harvesting (LH) complex, and transfers to the reaction center (RC), wherein primary charge separation occurs and transforms the energy into electrochemical potentials. In contrast to purple bacteria, R. castenholzii RC-LH (rcRC-LH) does not contain an H subunit. Instead, a tightly bound tetraheme cytochrome c subunit is exposed on the P-side of the RC, which contains three BChls, three bacteriopheophytins (BPheos), two menaquinones, and one iron for electron transfer. These novel structural features of the rcRC-LH are advantageous for enhancing the electron transfer efficiency and subsequent photo-oxidation of the c-type hemes. However, the photochemical properties of rcRC-LH and its applications in developing the photo-bioelectrochemical cells (PBECs) have not been characterized. Here, we prepared a PBEC using overlapped fluorine-doped tin oxide (FTO) glass and Pt-coated glass as electrodes, and rcRC-LH mixed with varying mediators as the electrolyte. Absence of the H subunit allows rcRC-LH to be selectively adhered onto the hydrophilic surface of the front electrode with its Q-side. Upon illumination, the photogenerated electrons directly enter the front electrode and transfer to the counter electrode, wherein the accepted electrons pass through the exposed c-type hemes to reduce the excited P+, generating a steady-state current of up to 320 nA/cm2 when using 1-Methoxy-5-methylphenazinium methyl sulfate (PMS) as mediator. This study demonstrated the novel photoelectric properties of rcRC-LH and its advantages in preparing effective PBECs, showcasing a potential of this complex in developing new type PBECs.

Three-dimensional tree-like branched TiO2 nanorods for the highly selective enrichment and determination of lead.

Branched titanium dioxide nanorods (B-TiO2 NRs) grown on fluorine-doped tin oxide glass (FTO) were developed, which can be usedas a solid-phase extractant for preconcentration and determination of trace Pb(II) combined with inductively coupled plasma optical emission spectrometry (ICP-OES). The B-TiO2 NR-based glass substrate displayed excellent adsorptive selectivity and capacity for Pb(II); the maximum adsorption capacity was found to be 168.4 mg⋅g-1 PB(II)at pH = 5.0. It proved that the primary extraction mechanism was attributed to soft acid/soft base interactions to form complexes for chemisorption. Investigating the adsorption kinetics and isotherms indicated that the pseudo-second-order and Langmuir models can better describe Pb(II) adsorption on the B-TiO2 NRs. Theproposed method presented good linearity from 0.01 to 5 mg⋅L-1 with a correlation coefficient (R2) of 0.9989 and a low limit of detection (LOD) of 2.2 μg⋅L-1 for Pb(II) under optimal conditions. The method was successfully applied to Pb(II) determination in foodstuffs with desirable recoveries from 93.18 to 108.1% and good precision with an RSD of less than 12.2%. This work provides a new strategy for selective extraction and determination of Pb(II) in complicated matrix samples.

Photoelectrocatalytic degradation of sulphonamide antibiotics in aquatic media using a novel Co-doped ZnO nanocomposite: evaluation of performance, kinetic studies

ABSTRACT It is well known that antibiotics’ residues in aquatic environments are a great threat to human health and ecology. Thus, it is vital to develop efficient strategies to overcome the mentioned threat and degrade the pointed out residues as much as possible. Herein, a novel Co-doped ZnO nanocomposite was fabricated and deposited on fluorine-doped tin oxide glass sheets (FTO) and eventually applied for the photoelectrocatalytic degradation of four sulphonamides (SAs), namely sulphacetamide (SCT), sulphathiazole (STZ), sulfamethoxazole (SMX) and sulphadiazine (SDZ) under visible light irradiation. In this regard, the effect of initial pH (3–11), applied current (0.5–1.5 mA/cm2), initial concentration of SAs (5–20 mg/L) were thoroughly investigated. The results indicated that under the optimal conditions (pH = 9, [SAs] = 5 mg/L and applied current = 1.5 mA/cm2), the degradation efficiencies obtained under a 90-min of reaction time were as follows: SCT (97.1%), SMX (95.8%), SDZ (93.2%) and STZ (91.8%). In addition, the degradation of the SAs by the applied photoelectrocatalytic process (PECP) followed the first-order kinetic model. Meanwhile, the applied PECP exhibited an excellent performance with regard to real samples. Finally, PECP is reckoned to be associated with ‘green’ technologies as electricity is involved and the used catalyst will not end up in the environment as secondary toxic materials.

Effects of Annealing Ambient on the Structural, Optical and Electrical Properties of TiO2:Ge Thin Films

TiO2, a semiconducting material with a wide energy band gap, has been researched intensively due to its interesting properties and many potential applications. The films properties can as well be modified by preparing the films under diverse ambient to suit diverse applications. In this work, the effects of the annealing atmosphere on the structural, optical and electrical properties of pure TiO2 and TiO2:Ge composite thin films deposited by sputtering from commercially available pure TiO2 and TiO2:Ge (85:15) targets respectively were studied. The films were deposited on fluorine doped tin oxide glass substrates by radio frequency magnetron sputtering technique at room temperature 23–25 ℃ and then annealed at 450 ℃ for one hour in three different atmospheres: air, argon and nitrogen. The XRD results revealed that, both pure TiO2 and TiO2:Ge thin films were crystalline and had a mixed phase of anatase and rutile regardless of the annealing ambient. The calculated crystallite sizes ranged between 19–21 nm with the particle sizes for TiO2:Ge films being larger compared to pure TiO2 as calculated from ImageJ software. Electrical measurements showed that the resistivity of as deposited pure TiO2 films (about 13.03 × 10–2 Ω-cm) was greater than the TiO2: Ge composite (5.91 × 10–2 Ω-cm). Furthermore, on annealing, pure TiO2 had a resistivity of 9.47 × 10–2 Ω-cm–10.4 × 10–2 Ω-cm, while the TiO2:Ge composite had a resistivity of 2.24 × 10–2 Ω-cm–3.61 × 10–2 Ω-cm depending on the annealing atmosphere. Variation of annealing atmosphere had minimal influence on the electrical resistivity of the films. The films annealed in nitrogen recorded the least resistivity values averaging about 5.86 × 10–2 Ω-cm, while those annealed in argon and air recorded a resistivity of 6.94 × 10–2 Ω-cm and 6.65 × 10–2 Ω-cm, respectively. The transmittance spectra showed that, all the annealed films were transparent in the visible region (400–700 nm) with a mean bandgap of 3.60 eV for each annealing atmosphere. It is recommended that films annealed in nitrogen atmosphere could be considered for potential applications in photovoltaics.
 Keywords: Titanium dioxide; Germanium; Ambient; Structural; Optical, Electrical

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO 2 Bioreduction

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO ₂ Bioreduction

Study of electrophoretic deposition of ZnO photoanodes on fluorine-doped tin oxide (FTO) glass for dye-sensitized solar cells (DSSCs)

Semiconductors, such as zinc oxide (ZnO), are used in different scientific fields, including energy. This study applied ZnO thin films on a photovoltaic cell, specifically a dye-sensitized solar cell (DSSC). ZnO was used in solar cells due to its characteristics such as electronic mobility. Electrophoretic deposition (EPD) is an efficient method to deposit thin films since it can be done at room temperature and its parameters can be easily controlled. ZnO thin films were deposited on fluorine-doped tin oxide (FTO) glass, changing the tension parameter, and used in a DSSC, with different dye immersion times, between 7 and 24 h, to observe time effects on cell efficiency. For lower tension, 30 and 40 V, 7 h improved the cell efficiency, and at 50 V, 24 h favored the current density and efficiency. The highest efficiency was for the photoanode EPD deposited at 50 V, for 24 h dye immersion, at about 2.68%, and photocurrent of 13.55 mA/cm2.

Binder-free mechanochemical metal-organic framework nanocrystal coatings.

The practical applications of metal-organic frameworks (MOFs) usually require their assembly into mechanically robust structures, usually achieved via coating onto various types of substrates. This paper describes a simple, scalable, and versatile mechanochemical technique for producing MOF nanocrystal coatings on various non-prefunctionalised substrates, including ZrO2, carbon cloth, porous polymer, nickel foam, titanium foil and fluorine-doped tin oxide glass. We revealed the detailed mechanisms that ensure the coating's stability, and identified the coating can facilitate the interfacial energy transfer, which allowed the electrocatalysis application of the MOF coating on conductive substrates. We further demonstrated that coatings can be directly generated in a one-pot fashion by ball milling MOF precursors with substrates.

Fabrication of Spin Coater Device using Hematocrit Centrifuge with Vacuum Substrate Holder for Thin Film Deposition

One of the most important thin film deposition techniques on a silicon, quartz or sapphire substrate in the world is the spin coating method. Hematocrit centrifuge was used to elaborately manufacture the spin coating machine from affordable materials without vibrations. The vacuum holder substrate in this system is used for substrate adhesion. This method provides a dimensionally free substrate with appropriate adhesion for sedimentation upon high-speed spinning. A platinum thin film was deposited on a fluorine-doped tin oxide glass (FTO) substrate with a specific concentration of hexa-chloro-platinic acid. Platinum thin films were investigated by Field Emission Scanning Electron Microscope (FESEM) and UV-Vis spectroscopy. FESEM displays successfully produced platinum thin films. The results showed a platinum film transmittance decrement with increasing of hexachloro-platinic acid content. Therefore, the suggested spin coater in this work can deposit platinum thin films with high transmittance up to (98 a.u.).

Controllable morphology of Bi2S3nanostructures formedviahydrothermal vulcanization of Bi2O3thin-film layer and their photoelectrocatalytic performances

AbstractBi2S3nanostructures with various morphologies were synthesized through hydrothermal vulcanization at different sulfur precursor (thiourea) concentrations. A 100 nm thick sputter-deposited Bi2O3thin-film layer on a fluorine-doped tin oxide glass substrate was used as a sacrificial template layer. The etching of the Bi2O3sacrificial template layer and the regrowth of Bi2S3crystallites during hydrothermal vulcanization produced the different Bi2S3nanostructure morphologies. The lowest sulfur precursor concentration (0.01 M) induced the formation of Bi2S3nanosheets, whereas the Bi2S3nanoribbons and nanowires were formed with increased sulfur precursor concentrations of 0.03 and 0.1 M, respectively. These results indicate that sputter-deposited Bi2O3thin-film layers can be effectively used to form low-dimensional Bi2S3crystals with controllable morphologies. Among the various Bi2S3samples, the Bi2S3nanosheets exhibited superior photoactive ability. The higher active surface area, surface defect density, light absorption capacity, and photo-induced charge separation ability of Bi2S3nanosheets explain their superior photoelectrocatalytic degradation ability of rhodamine B dyes.

Fabrication and Characterization of p-Cu2O on n-TiO2 Layer by Electrodeposition Method for Heterojunction Solar Cells Development

This study focused on the copper (I) oxide (Cu2O) that serves as an absorber layer, owing to its excellent optical properties, while titanium dioxide (TiO2) is a well-known material that has superior properties in solar cell development. In this work, the TiO2 nanorods layer was synthesised on a fluorine-doped tin oxide (FTO) glass substrate by a facile hydrothermal method followed by stacking the Cu2O layer using a low-cost electrodeposition method at different deposition times. Prior to deposition, a cyclic voltammetry (CV) measurement was performed, and the result showed that Cu2O films were successfully grown on the TiO2 nanorods layer with high uniformity. The crystallinity of the Cu2O/TiO2 film was increased when the deposition time was elevated. The strongest diffraction peak was detected in the sample deposited for 90 minutes. FE-SEM images revealed the formation of the pyramidal structure of Cu2O on the TiO2nanorod layer. The optical properties showed that the samples deposited at 60 minutes and above were red-shifted, with the estimated bandgap being slightly decreased when extending the deposition time. Meanwhile, the resistivity and sheet resistance of the as-prepared samples were increased. The performance of the solar cell was investigated, and the power energy conversion was slightly increased to 0.0267% for the heterojunction sample deposited at 90 minutes. Doi: 10.28991/HEF-2021-02-04-02 Full Text: PDF

In-situ grown metal-organic framework-derived carbon-coated Fe-doped cobalt oxide nanocomposite on fluorine-doped tin oxide glass for acidic oxygen evolution reaction

Development of stable and efficient non-noble metal based electrocatalysts for oxygen evolution reaction (OER) in acidic media is of great importance for proton exchange membrane based water electrolysis, which is indispensable for green hydrogen production. Herein, iron-doped, carbon-coated Co3O4 nanocomposite derived from a cobalt metal-organic framework, is grown in-situ on fluorine-doped tin oxide (FTO) glass (Fe-Co3O4@C/FTO) as an efficient and a stable binder-free electrode for acidic OER. Fe doping enhances both catalytic efficiency and stability of carbon coated Co3O4 toward acidic OER, through inducing small primary particle sizes and suitably modulated electronic structure of Co3O4, and better catalyst/substrate adhesion. Fe-Co3O4@C/FTO exhibits impressive electrocatalytic performances in 0.5 M H2SO4, with a low overpotential of 396 mV at 10 mA cm−2 and a small Tafel slope of 68.6 mV dec−1. Its electrochemical performances remain stable for over 50 h at 10 mA cm−2, making it a promising non-noble metal based electrocatalyst for acidic OER.

Sulphate radical enhanced photoelectrochemical degradation of sulfamethoxazole on a fluorine doped tin oxide - copper(I) oxide photoanode

• Visible light active FTO-Cu 2 O photoanode was successfully synthesised. • Sulphate radical was produced from persulphate salt at the surface of the Cu 2 O. • Degradation of sulfamethoxazole was markedly enhanced by sulphate radicals. • Mechanism of radicals generation and sulfamethoxazole degradation were proposed. • Application in real wastewater matrix was carried out with TOC removal of 43%. We report a sulphate radical enhanced photoelectrochemical degradation of sulfamethoxazole on a solar light driven fluorine doped tin oxide - copper(I) oxide photoanode. Copper(I) oxide was prepared by a template-free method and dispersed onto the surface of a fluorine doped tin oxide glass to form the photoanode. UV–Vis diffuse reflectance spectroscopy showed that the photoanode absorbed in the visible light region. With sodium persulphate as the source of sulphate radical, photoelectrochemical degradation studies showed that sodium persulphate markedly enhanced the degradation of sulfamethoxazole. Studies on the effects of change in concentration of the persulphate and the absence of the persulphate on the photoelectrocatalytic degradation process were conducted. Overall, the extent of degradation and mineralisation of sulfamethoxazole in water was found to be 86% and 67% respectively with bias potential of 1.5 V for the sulphate radical enhanced process. Scavenger studies showed that the photogenerated holes and sulphate radicals were the primary active species in the abatement of sulfamethoxazole. The effectiveness of sulfamethoxazole removal in real matrices by the use of FTO-Cu 2 O photoanode and sulphate radical was also confirmed.

A study of physico-chemical characteristics of electrochromic Ni(OH)2-PVA films on fto glass with different deposition duration

The use of electrochromic elements in “smart” windows leads to significant savings in electricity required for cooling premises. However, the high cost of these devices does not allow the technology to be widely used. Since the cost is determined by costly vacuum deposition methods, the development of other cheaper methods of deposition of electrochromic element layers is urgent. Aspects of alternative to vacuum formation methods – cathode template electrochemical deposition of composite electrochromic Ni(OH)2-PVA films were investigated. The study is devoted to determining the effect of the duration of deposition of the electrochromic layer on their physicochemical characteristics, in particular, on the optical and electrochemical properties. The deposition was carried out on fluorine-doped tin oxide glasses (FTO glasses). The time of deposition was chosen equal to 5, 10, 20, 40, 60, and 80 minutes. As a result of the experiments, it was shown that the optimal duration of deposition under the selected conditions of the electrochromic layer formation was the interval from 5 to 20 minutes, inclusive. The deposition time of 40 minutes did not improve the optical characteristics of the film. At the same time, with the deposition duration of 60 and 80 minutes, the electrochemical and optical parameters sharply decreased, the coloration depth and irreversibility during bleaching, as well as the specific capacitances of the processes decreased. In the course of data processing, the film thickness was calculated depending on the duration of deposition in several ways. Comparison of the graphs obtained made it possible to determine the approximate amount of polyvinyl alcohol in the electrochromic composite coating, as well as to estimate the current efficiency of the electrodeposition and oxidation-reduction process of the electrochromic material. In this case, the volume of polyvinyl alcohol in the composite was approximately equal to the volume of nickel hydroxide, and the efficiency of Ni(OH)2 deposition and coloration-bleaching processes was approximately 100 %

A Bifunctional Lead–Iron Oxyfluoride, PbFeO2F, That Drives Photoelectrochemical and Electrochemical Water Oxidation

Introduction Photoelectrochemical water splitting has attracted attention as a method of generating solar fuel, such as hydrogen that is expected to be utilize as a renewable energy carrier and clean fuel of an internal‐combustion engine.1 In the photoanode materials reported so far, ordinary metal oxides require ultraviolet light for operation because of their wide bandgaps (>3 eV), and visible-light-responsive metal oxides need an additional electrochemical bias because their conduction-band minimum is a lower position than the H+/H2 reduction potential. Mixed-anion compounds fascinating recent photocatalyst researchers possess visible-light response because of a narrow bandgap with less electronegative anion species.1,2 However, they are not very stable for water oxidation, because photogenerated holes oxidize the anion species except for oxygen in the compounds. Recently, we have reported an oxyfluoride Pb2Ti2O5.4F1.2 as a stable photoanode material that absorbs visible light at wavelengths as long as ~500 nm.3 The VBM of Pb2Ti2O5.4F1.2 is mainly composed by the O 2p orbitals. As the result, the Pb2Ti2O5.4F1.2 photoanode is essentially stable toward self-oxidation by photogenerated holes. However, this is the sole example of a visible-light-responsive oxyfluoride photoanode. Development of a new oxyfluoride photoanode absorbing visible light is important for enabling the further design of visible-light-responsive photoanode materials. In the present work, a lead–iron oxyfluoride PbFeO2F is applied to a photoanode material and electrocatalyst for water-oxidation. PbFeO2F, which can be synthesized by a high-pressure method,4 has been reported to show a yellow colour. Thus, it is expected to function as a visible-light-responsive photoanode material. Moreover, PbFeO2F containing Fe cation is possible to provide catalytic performance for water oxidation, which means that this material may also function as an electrocatalyst. Results and Discussion According to the previously reported method,4 PbFeO2F powder was synthesized. It was deposited on a fluorine-doped tin oxide (FTO) glass substrate by electrophoresis. The PbFeO2F/FTO electrode was subjected to post-necking treatment by immersing in 0.1 M Ti{OCH(CH3)2}4 –isopropanol solution to deposit TiO2 layer (TiO2/PbFeO2F/FTO electrode), followed by electrodeposition of cobalt phosphate (Co-Pi) cocatalyst (Co-Pi/TiO2/PbFeO2F/FTO electrode). Linear-sweep voltammetry of the as-prepared electrodes in 0.1 M K3PO4 solution was conducted under intermittent visible-light irradiation (Figure 1A). The PbFeO2F/FTO electrode exhibited no photocurrent response. By contrast, a slight photocurrent response was observed for the TiO2/PbFeO2F/FTO electrode because of mainly improved interparticle conductivity in the electrode. Furthermore, a clear anodic photocurrent was observed for the Co-Pi/TiO2/PbFeO2F/FTO electrode. Loading the Co-Pi cocatalyst, known as a water-oxidation promoter, improved charge transfer at the electrode/water interface and charge separation from the surface to the bulk. Besides, the Co-Pi/TiO2/PbFeO2F/FTO electrode exhibited an anodic photocurrent under visible-light irradiation with wavelengths as long as ~600 nm. It indicates that PbFeO2F can function as a photoanode material under a wide range of visible-light wavelengths. Controlled-potential electrolysis with the as-prepared PbFeO2F/FTO electrode was operated at +1.7 V vs. RHE under dark conditions (Figure 1B). The evolved O2 was observed by GC analysis in the measurement. It was almost one-fourth the amount of electrons, which flowed during the electrolysis, giving a high Faradaic efficiency of 97%. This result means that the water oxidation was the major path at the PbFeO2F/FTO electrode. In addition, α-Fe2O3/FTO electrode does not work at this potential because of the larger overpotential than the PbFeO2F/FTO electrode for water oxidation. It reveals that PbFeO2F can also function as an electrocatalyst at a relatively low overpotential for water oxidation. References Seo, H. Nishiyama, T. Yamada and K. Domen, Visible-Light-Responsive Photoanodes for Highly Active, Stable Water Oxidation, Angew. Chem. Int. Ed., 57, 8396 (2018).Miyoshi and K. Maeda, Recent Progress in Mixed‐Anion Materials for Solar Fuel Production, Solar RRL, in press.Hirayama, H. Nakata, H. Wakayama, S. Nishioka, T. Kanazawa, R. Kamata, Y. Ebato, K. Kato, H. Kumagai, A. Yamakata, K. Oka and K. Maeda, Solar-Driven Photoelectrochemical Water Oxidation over an n-Type Lead-Titanium Oxyfluoride Anode, J. Am. Chem. Soc., 141, 17158 (2019).Inaguma, J.-M. Greneche, M.-P. Crosnier-Lopez, T. Katsumata, Y. Calage and J.-L. Fourquet, Structure and Mössbauer Studies of F−O Ordering in Antiferromagnetic Perovskite PbFeO2F, Chem. Mater., 17, 1386 (2005). Figure 1

Ultraviolet photodetector based on p-borophene/n-ZnO heterojunction

Borophene has attracted enormous attention because of its rich and unique structural and electronic properties for promising pratical applications. Although borophene sheets have been realized on different substrates in recent experiments, there are very few reports on the device application of borophene. Recently, borophene can be grown on some functional substrates, which lays a good foundation for its potential applications. Here, we report that hydrogenated borophene can be grown on the fluorine-doped tin oxide glass substrate. The phase of the obtained borophene is well consistent with the predicted semiconducting δ 5-boron sheet. Furthermore, a vertical heterojunction ultraviolet detector based p-borophene/n-zinc oxide was fabricated. The photoresponsivity of the detector is 1.02 × 10−1 A W−1, the specific detection rate was 1.43 × 109 Jones and the response speed was τ res = 2.8 s, τ rec = 3.2 s at the reversed bias of −5 V under the light excitation of 365 nm. This work will lay a foundation for further study on the attractive properties and applications of borophene in new optoelectronic devices and integrated circuits.