Fluorine-doped Tin Oxide Electrode Research Articles

Free-standing polyaniline-reduced graphene oxide (PANI-rGO) thermoelectric films via electrochemical synthesis

Abstract Heat-based energy harvesting is gaining attention as an alternative energy source. Thermoelectric materials (TEs) generate voltages in response to a thermal gradient and conductive polymer-carbon composites have properties that make them favorable for these applications. Polyaniline-reduced graphene oxide (PANi-GO) thermoelectric thin films were fabricated by the electropolymerization of PANi with simultaneous co-deposition of graphene onto fluorine-doped tin oxide (FTO). Poly(butyl acrylate) was spin-coated onto these films as backing support to make a stable free-standing film of PANi-rGO. The free-standing film was formed upon GO reduction which resulted in simultaneous delamination from the FTO electrode. Compositional and morphological data were obtained via Raman microspectroscopy and scanning electron microscopy and the TE properties were measured in terms of the Seebeck coefficient and conductivities from Hall effect measurements. The Seebeck coefficients of the films measured between 6.6 μV K−1 to 13.4 μV K−1, whereas Hall effect conductivities ranged from 0.483 to 2.68 S cm−1. The highest film power factor measured was 0.025 μW m−1K−2. Varying the GO content used in the electropolymerized film did not have a significant effect on the overall TE property though varying the reduction cycle number and voltage resulted in significant changes in the film Seebeck coefficients and conductivities.

Is the oxygen plasma cleaning technique indicated for any electrochemical purpose?: The case of FTO electrodes

Fluorine-doped tin oxide (FTO) is among the most used transparent conductive oxides (TCOs) in phototovoltaic devices such as photoelectrochemical and solar cells. Preparation of films on these TCOs can be achieved by several deposition techniques including electrodeposition. Among the several cleaning and activation procedures before a thin film deposition there is the oxygen plasma treatment, which has been successfully applied on several kind of substrate materials. Surprisingly, the use of this step on TCOs previously to the electrodeposition of a film is not a usual practice. Here we present a detailed study on the consequences of oxygen plasma process over FTO electrodes that are subsequently employed in several electrochemical reactions of practical importance. Open circuit potential (OCP) measurements from oxygen plasma treated FTO have proven the resorption of ions and/or solvent molecules in aqueous electrolyte following a pseudo-second order kinetic. Electrochemical reactions were quite sensible to the oxygen plasma treatment, even under mild conditions. In all cases FTO become deactivated for such electrochemical processes independently of the plasma set up employed except for metal electrodeposition. Partial recovering of the electrochemical response of FTO in the ferri/ferro system after annealing at 450 °C explains why oxygen plasma process is worthy only for other deposition techniques such as spray pyrolysis where similar temperatures are employed. Electrochemical Impedance Spectroscopy (EIS) analysis revealed a decrease of the majority carrier density (ND). This is mainly attributed to the oxyanion implantation on oxygen vacancies sites during the plasma process thus explaining the loss of activation of FTO. Energy level diagrams reveal the decrease of degeneracy of FTO towards an n-type semiconducting SnO2 film which is also supported by ultraviolet photoelectron spectroscopy (UPS). A band gap energy dependence with the plasma conditions allowed to check the filling of oxygen vacancies on the FTO surface without discard the loss of fluorine. Anodic polarization in acid media proved the impossibility of oxygen vacancies restitution, being the dominating process the partial etching of FTO.

Ultrasensitive detection of holoTC for analysis of Vitamin B12 levels using Ag2MoO4 deposited PEDOT sensing platform

Vitamin B12 is an essential micronutrient required for the proper functioning of the human body. Vitamin B12 deficiency is primarily causative of various neurolological disorders alongwith recurrence of oral ulcers and burning sensations which are early signs of condition such as pernicious anemia. Other complications associated with Vitamin B12 deficiency include risk of heart failure due to anemia, risk of developing autoimmune disorders and gastric cancer. Therefore, to obstruct these communal health issues, early detection of Vit B12 is highly needed. However, screening of vitamin B12 insufficiency is hindered by the low sensitivity of the conventional vitamin B12 test. Holotranscobalamin (holoTC) is an early indicator of the negative vitamin B12 balance as it is the first protein to decline in the serum. We report a novel impedimetric immunosensor based on flower-like poly (3,4-ethylenedioxythiophene) (PEDOT) nanostructural film impregnated with silver molybdate nanoparticles (Ag2MoO₄ NPs) deposited on fluorine-doped tin oxide electrode. The prepared electrodes were characterized by Field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and electrochemical studies. The activated anti-holoTC antibody was immobilized and optimized to capture the target in a response time of 15 min. The electrochemical performance of the sensor was carried out by using the electrochemical impedance spectroscopy technique (EIS) and a good linear relationship between ΔRct and holoTC was obtained in the range from 0.1 pg mL−1 to 100 ng mL−1 with a detection limit of 0.093 pg mL−1. The proposed sensor was successfully applied in human serum samples for holoTC detection. The experimental results showed that the immunosensor is highly selective towards holoTC and presented an acceptable stability of 20 days with reproducibility RSD ≤4%. To the best of our knowledge, this is the first developed electrochemical immunosensor for holoTC detection.

Surface-engineered vertically-aligned ZnO nanorod for sensitive non-enzymatic electrochemical monitoring of cholesterol

Developing highly sensitive and selective non-enzymatic electrochemical biosensors for disease biomarker detection has become challenging in healthcare applications. However, advances in material science are opening new avenues for creating more dependable biosensing technologies. In this context, the present work introduces a novel approach by engineering a hybrid structure of zinc oxide nanorod (ZnO NR) modified with iron oxide nanoparticle (Fe2O3 NP) on an FTO electrode. This Fe2O3 NP-ZnO NR hybrid material functions as a nanozyme, facilitating the catalysis of cholesterol and enabling the direct transfer of electrons to the fluorine-doped tin oxide (FTO) electrode, limiting the need for costly and traditional enzymes in the detection process. This innovative non-enzymatic cholesterol biosensor showcases remarkable sensitivity, registering at 642.8 μA/mMcm2 within a linear response range of up to 9.0 mM. It also exhibits a low detection limit (LOD) of ∼12.4 μM, ensuring its capability to detect minimal concentrations of cholesterol accurately. Moreover, the developed biosensor displays exceptional selectivity by effectively distinguishing cholesterol molecules from other interfering biological species, while exhibiting outstanding stability and reproducibility. Our findings indicate that the Fe2O3 NP-ZnO NR hybrid nanostructure on the FTO electrode holds promise for enhancing biosensor stability. Furthermore, the present device fabrication platform offers versatility, as it can be adapted with various enzymes or modified with different metal oxides, potentially broadening its applicability in a wide range of biomarkers detection.

Insulated π-Conjugated Azido Scaffolds for Stepwise Functionalization via Huisgen Cycloaddition on Metal Oxide Surfaces.

In organic-inorganic hybrid devices, fine interfacial controls by organic components directly affect the device performance. However, fabrication of uniformed interfaces using π-conjugated molecules remains challenging due to facile aggregation by their strong π-π interaction. In this report, a π-conjugated scaffold insulated by covalently linked permethylated α-cyclodextrin moiety with an azido group is synthesized for surface Huisgen cycloaddition on metal oxides. Fourier-transformed infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy confirm the successful immobilization of the insulated azido scaffold on ZnO nanowire array surfaces. Owing to the highly independent immobilization, the scaffold allows rapid and complete conversion of the surface azido group in Huisgen cycloaddition reactions with ethynyl-terminated molecules, as confirmed by FT-IR spectroscopy monitoring. Cyclic voltammetry analysis of modified indium tin oxide substrates shows the positive effects of cyclic insulation toward suppression of intermolecular interaction between molecules introduced by the surface Huisgen cycloaddition reactions. The utility of the scaffold for heterogeneous catalysis is demonstrated in electrocatalytic selective O2 reduction to H2O2 with cobalt(II) chlorin modified fluorine doped tin oxide electrode and photocatalytic H2 generation with iridium(III) dye-sensitized Pt-loadedTiO2 nanoparticle. These results highlight the potential of the insulated azido scaffold for a stepwise functionalization process, enabling precise and well-defined hybrid interfaces.

Photoelectrochemical determination of sulfide in water using a silver iodide/gold nanoparticle/fluoride-doped tin oxide electrode

Sulfides are widely used as industrial raw materials, but they also cause serious water pollution and pose a high risk to human health. Consequently, sensitive and selective methods for detecting sulfide ion (S2−) in water are required. In this work, a photoelectrochemical (PEC) sensor was proposed based on the precipitation-dissolution equilibrium between silver iodide (AgI) and S2− on a gold nanoparticle (AuNP)-modified fluorine-doped tin oxide (FTO) electrode. The sensor was characterized by scanning electron microscopy, X-ray diffraction, and UV–Vis spectroscopy and applied to detect S2− by measuring the photocurrent under Xe lamp irradiation. On the formation of Ag2S, the UV–Vis absorption spectrum of the electrode was red shifted and the absorbance increased significantly. Further, the photocurrent polarity was reversed as a result of the formation of Ag2S on the surface of AgI/AuNP FTO. Overall, the sensor showed high sensitivity and selectivity for S2− detection, and the detection was linear at 0.2–5.0 and 5.0–50.0 μmol/L with a limit of detection of 0.08 μmol/L. Crucially for practical applications, the sensor was reproducible and showed good recovery and accuracy in real samples. In summary, the proposed sensor owns advantages in simple fabrication, high sensitivity, selectivity, stability, and low cost, and has good application prospects in the environmental monitoring of S2−.

Enhancement capacitance of FTO electrodes via the electrospun ZnO thin film coating for supercapacitor applications; the role of dopants

The present study aimed to investigate the electrochemical performance of nanostructured ZnO thin films (TFs) on the fluorine-doped tin oxide (FTO) substrate. The pure ZnO TFs, Al-doped ZnO TFs, and Cu-doped ZnO TFs were fabricated using electrospinning and post calcination at 400 °C. The electron microscopy studies revealed that electrospun nanofiber masks changed to dense TFs with an average thickness of 250–290 nm constructed by 10–20 nm connected nanoparticles (NPs). The doping of Al and Cu into ZnO TFs increased the hydrophilicity. Cyclic voltammetry (CV), electrochemical impedance (EIS), charge-discharge profiles, and Mott-Schottky (M − S) analysis were performed on the samples to evaluate the capacitance performance of pure and doped ZnO TFs. The semiconductor of TFs was n-type. The results confirm that all films can be used as a supercapacitor. Also, our results suggest that Cu-doped ZnO (CZO) TFs are the best choice for a supercapacitor electrode due to their 1.14 F cm−2 areal capacitance at 1 mA cm−2 applied current.

Study on Influence Factors of H2O2 Generation Efficiency on Both Cathode and Anode in a Diaphragm-Free Bath.

Electrosynthesis of H2O2 via both pathways of anodic two-electron water oxidation reaction (2e-WOR) and cathodic two-electron oxygen reduction reaction (2e-ORR) in a diaphragm-free bath can not only improve the generation rate and Faraday efficiency (FE), but also simplify the structure of the electrolysis bath and reduce the energy consumption. The factors that may affect the efficiency of H2O2 generation in coupled electrolytic systems have been systematically investigated. A piece of fluorine-doped tin oxide (FTO) electrode was used as the anode, and in this study, its catalytic performance for 2e-WOR in Na2CO3/NaHCO3 and NaOH solutions was compared. Based on kinetic views, the generation rate of H2O2 via 2e-WOR, the self-decomposition, and the oxidative decomposition rate of the generated H2O2 during electrolysis in carbonate electrolytes were investigated. Furthermore, by choosing polyethylene oxide-modified carbon nanotubes (PEO-CNTs) as the catalyst for 2e-ORR and using its loaded electrode as the cathode, the coupled electrolytic systems for H2O2 generation were set up in a diaphragm bath and in a diaphragm-free bath. It was found that the generated H2O2 in the electrolyte diffuses and causes oxidative decomposition on the anode, which is the main influent factor on the accumulated concentration in H2O2 in a diaphragm-free bath.

Photoelectrochemical quenching-recovery biosensor based on NSCQDs/Fe2O3@Bi2S3 for the detection of trypsin

BackgroundThe content of trypsin will change when pancreatic diseases occur, therefore developing a high-performance method for trypsin detection is of great significance for guiding patients on medication plans and improving their prognosis. Photoelectrochemical (PEC) analysis techniques have emerged as a solution to apply for bioassays. ResultsHerein, the Fe2O3@Bi2S3 and Nitrogen and sulfur co-doped carbon quantum dots (NSCQDs) were successfully synthesized by a hydrothermal method. Subsequently, NSCQDs/Fe2O3@Bi2S3 with a photocurrent amplification effect covered on fluorine-doped tin oxide (FTO) electrode as the substrate material and apoferritin (APO) as a bio-recognition element to quench the photocurrent of the substrate material which can be excited with light. Due to the decomposition specifically between APO and trypsin, the photocurrent response increased. The linear range for trypsin detection showed satisfied results from 2 to 1000 ng mL−1 under optimal conditions, with a detection limit of 0.42 ng mL−1 and a recovery rate of 97.41 %–103.02 %, enabling efficient quantitative analysis of trypsin. SignificanceIn this experiment, a PEC biosensor with simple operation, low detection limit, excellent selectivity and strong stability was successfully prepared, enabling quantitative analysis of trypsin in human serum samples through the quenching-recovery mechanism. It holds great significance for diagnosis and serves as a practical method for the detection of trypsin in the future.

In-Depth Analysis on the Fabry-Perot Effect of Cs2AgBiBr6 Double Perovskite-Based Solar Cells via Optical Path Length Modulation

Herein, the Fabry-Perot (F-P) interference of cesium silver bismuth bromide (Cs2AgBiBr6) double perovskite solar cells has been analyzed by modulating the optical path length of each layer step by step using the finite-difference time-domain (FDTD) method. The study was performed pass through three main steps. In step 1, for the fluorine-doped tin oxide (FTO)/Cs2AgBiBr6 double perovskite/gold (Au) architecture, we increased the absorption layer thickness from 150 to 600 nm at intervals of 150 nm and then predicted the optical performance including the absorption and reflection. In step 2, titanium dioxide (TiO2) layer was added between FTO electrode and Cs2AgBiBr6 double perovskite and then scaled from 20 to 200 nm at intervals of 20 nm. In the analysis process, short-circuit current density (Jsc) repeatedly fell and rose as the TiO2 layer thickness increased, and when TiO2 layer thickness is 100 nm, Jsc showed the highest value of 13.91 mA/cm2. In step 3, by applying a spiro-OMeTAD layer between the Cs2AgBiBr6 double perovskite absorption layer and Au electrode, the Jsc showed a continuous increase with slight decrease as the spiro-OMeTAD layer thickness increased from 110 to 200 nm, and when the spiro-OMeTAD layer thickness was 200 nm, Jscwas calculated as 14.57 mA/cm2, which is the highest value in the range. In the case of the optimal condition of full structure device, the Fabry-Perot resonance peaks were discovered at 477, 520, 572, 659, and 778 nm five wavelength regions, and the influence of the Fabry-Perot resonance on the generation rate inside the absorption layer on the 520, 572, and 659 nm monochromatic wavelength light was analyzed according to the position in the device. Our study approaches the Cs2AgBiBr6 double perovskite solar cell from an F-P cavity perspective and shows the light trapping phenomenon of the device according to the optical path length modulation.

Cerium Ion Adsorption to Fluorine-Doped Tin Oxide Electrodes

The f-elements are critical in many technologies including electronics, catalysis, magnetics, and clean energy. Additionally, these elements occur in very low abundance worldwide. Research has therefore been motivated in the detection, quantification, and reclamation of these elements from waste streams. In this presentation we explore the use of fluorine-doped tin oxide (FTO) electrodes as sensitive and cost-effective electrochemical sensors for cerium ions. We demonstrate that cerium adsorbs reversibly to bare FTO surfaces with a dependence on pH. Through voltammetry and XPS characterization, we demonstrate that the adsorbed cerium, which can undergo the quasi-reversible CeIV/CeIII redox transition, exists in more than one chemical environment. Based on these data, we posit that these different environments are due to the buildup of multiple layers of cerium ions on the FTO surfaces. At lower concentrations (< ca. 100 uM), we can use voltammetry to quantify the cerium adsorbed to the FTO and relate it to the concentration of cerium in solution, with a lower detection limit of about 10-6 M. The data fits to a pseudo second order rate law with a rate constant on the order of 107 (cm2 mol-1)2 s-1. The adsorption fits well to the Freundlich model, but we are working towards finding a non-empirical adsorption model than provide the equilibrium constant for the adsorption reaction.

Aptasensor for ovarian cancer biomarker detection using nanostructured gold electrodes.

The development of an electrochemical aptasensor for the detection of CA125 as an ovarian cancer biomarker using gold nanostructures (GNs) modified electrodes is reported. The GNs were deposited on the surface of fluorine-doped tin oxide electrodes using a simple electrochemical method and the effects of pH and surfactant concentration on the topography and electrochemical properties of the resulting GNs modified electrodes were investigated. The electrodes were characterized using field-emission scanning electron microscopy and X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. The best electrode, in terms of the uniformity of the deposited GNs and the increase in electroactive surface area, was used for development of an aptasensor for CA125 tumor marker detection in human serum. Signal amplification was done by using aptamer-conjugated gold nanorods resulting in the detection limit of 2.6 U/ml and a linear range of 10 to 800 U/ml. The results showed that without the need for expensive antibodies, the developed aptasensor could specifically measure the clinically relevant concentrations of the tumor marker in human serum.

Rod-Shaped Spinel Co3O4 and Carbon Nitride Heterostructure-Modified Fluorine-Doped Tin Oxide Electrode as an Electrochemical Transducer for Efficient Sensing of Hydrazine.

Engineering low-cost and efficient materials for sensing hydrazine (HA) is critical given the adverse effects of high concentrations on humans. We report an efficient electrode made up of rod-shaped Co3O4/g-C3N4 (Co3O4/graphitic carbon nitride (GCN))-coated fluorine-doped tin oxide as a desirable electrode for the detection of HA. GCN is synthesized by the thermal decomposition of melamine, Co3O4, and the heterostructure is grown by a hydrothermal process. The as-prepared materials were characterized by using spectroscopic and microscopic techniques. The voltammetric studies showed that HA can be oxidized at a lower onset potential of 0.24 V vs reference Ag/AgCl, and the composite yielded a significantly enhanced oxidation peak current than the pure components because of the high electrocatalytic activity and the synergy between Co3O4 and GCN. By employing chronoamperometry, the proposed sensor can detect HA in a wide range with a high sensitivity of 819.52 μA mM-1 cm-2 and a detection limit of 3.14 μM. The high conductivity of Co3O4, enhanced electroactive surface area, the rich redox couples of Co2+/Co3+, and the additional catalytic sites from GCN are responsible for the high performance of the heterostructure.

Unveiling the influence of ferromagnetic Gd-doped ZnO films on the performance of organic solar cells

Organic solar cells (OSCs) have emerged as a promising technology for renewable energy generation due to their low cost, lightweight, flexibility, and compatibility with roll-to-roll manufacturing. However, OSCs still face challenges in achieving high power conversion efficiency (PCE) due to various factors, including recombination loss. In this study, we investigated the effect of introducing a layer of eight atomic percent gadolinium-doped zinc oxide (Zn0.92Gd0.08O) between the poly(3-hexylthiophene) (P3HT): [6,6]-phenyl butyric acid methyl ester (PCBM) active layer and the fluorine-doped tin oxide (FTO) electrode of the OSC. The reference cell, which has an Au/P3HT:PCBM/ZnO/FTO structure, exhibits a PCE of 0.52%. Remarkably, when the Zn0.92Gd0.08O layer was inserted (Au/P3HT:PCBM/Zn0.92Gd0.08O/FTO), the PCE increased significantly to 3.42%, which is more than six times the increase. Through further analysis, we present that the insertion of the Zn0.92Gd0.08O layer induces spin polarization in the P3HT:PCBM layer, leading to enhanced charge transport and reducing the recombination rate. Based on the findings, it can be concluded that the Zn0.92Gd0.08O film can potentially improve OSC performance.

Assessing stability and performance of fluorine-doped tin oxide electrodes for peroxide formation in carbonate-based electrolytes

Hydrogen peroxide (H2O2) is a valuable chemical currently produced industrially on a large scale by the anthraquinone process. Recently, carbonate and/or bicarbonate-induced selective water oxidation to hydrogen peroxide has been suggested as an environmentally friendly alternative. In this manuscript, we discuss the effect of electrolyte concentration and type of cation in selective water oxidation using carbonate-based electrolytes (i.e., Na2CO3, K2CO3 and Cs2CO3) on fluorine-doped tin oxide (FTO) electrodes. Based on the experimental observations and a techno-economic evaluation we reveal that K2CO3 is preferred over Na2CO3 and Cs2CO3 electrolytes. Using 5 M K2CO3 a Faradaic efficiency of > 60 % was achieved at industrially relevant current densities of 100 mA cm−2. Although for 5 M Cs2CO3 electrolytes lower potentials are required at otherwise similar process conditions, a lower efficiency for hydrogen peroxide formation has been observed which is assigned to higher degradation in Cs-containing electrolyte, rendering the use of potassium-based electrolytes more efficient. Independent of the electrolyte used, the electrodes suffered from stability issues as revealed by increasing concentrations of tin in the electrolyte and electrode failure after polarization for several hours. Overall, this work provides detailed knowledge about the impact of electrolyte concentration and type of cation and reveals the importance of appropriate cell design and process operation for meaningful hydrogen peroxide synthesis by mediated-anodic water oxidation.

Extending Silver Nanowire Modified Electrodes to Industrial Zinc Electrolyte for Copper Ion Detection

Real-time and rapid determination of trace copper ion (Cu2+) in the electrolyte of zinc smelting process is urgently needed. However, the complicated composition of the electrolyte, especially the extremely high-concentration of zinc ion (Zn2+) may cause severe interference to the detection of Cu2+. This work describes a facile electrochemical sensor for Cu2+ determination in the electrolyte of zinc smelting plants based on a fluorine-doped tin oxide (FTO) electrode with silver nanowires (AgNWs) and Nafion modification. The AgNWs/Nafion-FTO electrode showed good detection ability with the linear detection range of 0.2−2 mg l−1 Cu2+ in 45 g l−1 Zn2+ solution using differential pulse anodic stripping voltammetry (DPASV) technique. With DPASV technique, Cu2+ can be first reduced and pre-concentrated on the working electrode surface at −0.6 V vs Ag/AgCl for 500 s, after which the deposited Cu metal is oxidized around 0 V vs Ag/AgCl during the stripping step. It has been proved by transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS) that trace Cu2+ can be adsorbed and reduced on AgNWs in solutions with Zn/Cu ratio up to (2.25−22.5) × 104. The results extend AgNWs modified electrode to the industrial solution, providing a new strategy for detection of trace metal ions in industrial solutions.

Bifunctional Lead–Iron Oxyfluorides, 3D Cubic PbFeO2f and 2D Layered Pb3Fe2O5F2, Driving Photoelectrochemical and Electrochemical Water-Oxidation

Introduction Photoelectrochemical water splitting has attracted attention as a method of generating solar fuel such as hydrogen gas to be useful as a renewable energy carrier and a clean fuel of an internal‐combustion engine. For water oxidation of the half reaction in the water splitting, mixed-anion compounds have appeared as good candidates of the catalyst. In the mixed-anion compounds, a metal center is coordinated by several kind of anionic species. This environment induces their wide variety of physical and chemical properties not to be realized in single anion counterparts. The mixed-anion compounds possess visible-light responsibility and can utilize sunlight efficiently, therefore, which have fascinated photocatalyst researchers. The reason why they absorb visible light is the narrow bandgap with less electronegative anion species than oxygen. However, they are not very stable for photoelectrochemical water-oxidation because photogenerated holes oxidize the anion species except for oxygen in the compounds and cause degradation. Recently, we have reported an oxyfluoride Pb2Ti2O5.4F1.2 as a stable photoanode material that absorbs visible light at wavelengths up to ~500 nm.1 Oxyfluoride containing O2− and F− anions in the same phase is an example of the mixed-anion compounds. The other anion F− is less oxidized than O2−. Thus, the Pb2Ti2O5.4F1.2 photoanode showed essential stability toward the degradation by photogenerated holes exceptionally. However, this is the sole example of a visible-light-responsive oxyfluoride photoanode. Development of a new oxyfluoride photoanode absorbing visible light is important to gain the insight for water oxidation using the oxyfluorides. In the present work, another type of lead-iron oxyfluorides, PbFeO2F and Pb3Fe2O5F2, are applied to water oxidation as not only a photoanode but also an electrocatalyst.2,3 The lead-iron oxyfluoride, PbFeO2F, drives photoelectrochemical water-oxidation in visible light up to ~600 nm. In addition, this oxyfluoride functions as the electrocatalyst for water oxidation.2 In the electrochemical water-oxidation, another Pb3Fe2O5F2 shows higher performance for water oxidation than PbFeO2F. It seems that the crystal structure of two-dimensional layered perovskite Pb3Fe2O5F2 influences the superior performance to three-dimensional cubic perovskite PbFeO2F.3 Results and Discussion PbFeO2F and Pb3Fe2O5F2 powder were synthesized through a solid-state reaction and that in the evacuated glass tube, respectively.2,3 They were deposited on a fluorine-doped tin oxide (FTO) glass substrate by using electrophoresis method. The PbFeO2F or Pb3Fe2O5F2/FTO electrode was subjected to post-necking treatment to deposit TiO2 layer (TiO2/PbFeO2F or Pb3Fe2O5F2/FTO electrode), followed by electrodeposition of cobalt phosphate (Co-Pi) cocatalyst (Co-Pi/TiO2/PbFeO2F or Pb3Fe2O5F2/FTO electrode). Linear-sweep voltammetry for the as-prepared electrodes was conducted under intermittent visible-light irradiation (>400 nm) in 0.1 M K3PO4 solution (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. The Co-Pi cocatalyst, known as a water-oxidation promoter, improved the charge transfer at the electrode/water interface and charge separation in the electrode. Meanwhile, the Co-Pi/TiO2/PbFeO2F/FTO electrode exhibited an anodic photocurrent in visible light with longer wavelengths than ~600 nm. These tendencies were like those of Pb3Fe2O5F2 electrodes though the photocurrent were slightly higher than the PbFeO2F electrodes (Figure 1A, right). On contrary to the photoelectrochemical water-oxidation, a clear difference was observed when using those lead-iron oxyfluorides as an electrocatalyst. Under dark conditions, controlled-potential electrolysis with non-modified PbFeO2F and Pb3Fe2O5F2/FTO electrode was performed at +1.7 V vs. RHE (Figure 1B). The evolved O2 was detected by GC analysis in the measurement. The amount of that was almost one-fourth of electrons flowed during the electrolysis, which means the water oxidation was the major path for the electrochemical reaction. Besides, Pb3Fe2O5F2/FTO electrode showed 8 times higher activity than PbFeO2F. That reason has not been revealed but the difference is likely to be attributed to two-dimensional layered perovskite Pb3Fe2O5F2 and three-dimensional cubic perovskite PbFeO2F. References 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).Mizuochi, K. Izumi, Y. Inaguma and K. Maeda, A bifunctional lead–iron oxyfluoride, PbFeO2F, that functions as a visible-light-responsive photoanode and an electrocatalyst for water oxidation, RSC Adv., 11, 25616 (2021).Mizuochi, K. Oka, Y. Inaguma and K. Maeda, A two-dimensional perovskite oxyfluoride Pb3Fe2O5F2 as a catalyst for electrochemical oxidation of water to oxygen, Sustain. Energy Fuels, 6, 2423 (2022). Figure 1

Fabrication and characterization of NFMA/FTO electrochemical thin film by electrodeposition and immersion techniques: An effective detector for H2O2 and sunlight-driven MB degradation

Surface-confined electroactive nanoscale materials (organometallic semiconductors) are being explored as promising alternatives to traditional inorganic semiconductors for redox processes. In response to widespread non-biodegradable dye pollution causing severe environmental threats, urgent and effective methods for dye elimination or conversion are crucially needed. In this study, we successfully fabricated an electrochemical thin film of N-(ferrocenylmethyl) aniline (NFMA) on a fluorine-doped tin oxide (FTO) electrode using immersion and electrochemical deposition techniques. To characterize the NFMA/FTO electrode, we employed XRD, SEM, and UV–Vis spectroscopy. Our results revealed that the deposited NFMA/FTO films exhibited an amorphous structure, as confirmed by XRD analysis. SEM images demonstrated a uniform distribution of small particles on the FTO surface. UV–Vis spectroscopy showed favorable optical properties, indicating a direct band gap of 2.4 eV for electrodeposition film. The NFMA/FTO thin film outperformed FTO electrodes, exhibiting hydrophobic surfaces with contact angles of 73.89° and 78° for immersion and electrodeposition, respectively. The NFMA/FTO electrode exhibited effective electrochemical catalysis for hydrogen peroxide (H2O2) utilizing ferrocene/ferricenium (Fc/Fc+) as an electron-transfer mediator. Under sunlight irradiation, the NFMA/FTO thin film exhibited remarkable degradation efficiency of Methylene Blue (MB), achieving 78% degradation within a reaction duration of 180 min at a concentration of 1 ppm in a 500 mL. The degradation kinetics were found to follow the pseudo-first-order reaction model, yielding rate constant (k) values of 0.0078 min−1. Our findings highlight the potential of surface-confined electroactive nanoscale materials, particularly the NFMA/FTO system, as a promising avenue for various electrochemical and photocatalytic applications.

Photoelectrochemical aptasensing of lincomycin based on a AgI-carboxylated multiwalled carbon nanotubes-BiOI Z-scheme heterojunction

Lincomycin (LIN) is a common antibiotic that is widely used in animal husbandry and other fields, and the residual problem caused by its abuse has attracted widespread attention. Herein, a novel AgI-carboxylated multiwalled carbon nanotubes (cMWCNT)-BiOI Z-scheme heterojunction material was synthesized via a one-pot hydrothermal method, modified on a fluorine-doped tin oxide (FTO) electrode surface, and used for detecting LIN. The photocurrent on the AgI-cMWCNT-BiOI/FTO photoelectrode is 4.6 times that on the control AgI-BiOI/FTO photoelectrode. An amino-functionalized LIN aptamer was fixed on the AgI-cMWCNT-BiOI/FTO photoelectrode by the cross-linking reaction between chitosan and glutaraldehyde, and then Ru(NH3)63+ was electrostatically attached to the LIN aptamer to increase the photocurrent response to the LIN binding. When LIN binds competitively with Ru(NH3)63+ to the aptamer, the photocurrent signal can be quantitatively decreased. Under optimized conditions, the anodic photocurrent at 0 V vs KCl-saturated calomel electrode in 0.1 M phosphate buffer (pH 7.0) containing 0.100 M ascorbic acid was linear with the common logarithm of LIN concentration from 10.0 pM to 500 nM, with a limit of detection of 2.8 pM (S/N = 3). Satisfactory recovery results were obtained in the analysis of cow milk samples.

Mechanistic insight into efficient electrocatalysis for hydrogen evolution by a platinum film prepared on an FTO electrode using a mixed metal-imidazole casting method

A Pt nanoparticle (Pt(w-MI)) film was prepared on a fluorine-doped tin oxide (FTO) conducting substrate from a precursor solution containing H2PtCl6 in a mixed solvent of methanol/1-methyimidasol (MI) (3:1 v/v) by a mixed metal-imidazole casting (MiMIC) method. The Pt(w-MI) film is the uniformly dense morphology composed of compacted and well-connected Pt nanoparticles compared to the hollow morphology for the Pt(w/o-MI) film fabricated without MI. The Pt(w-MI)/FTO cathode showed efficient and durable HER activities, generating a current density of 10 mA cm−2 at an overpotential (η10) of 198 mV, a Tafel slope of 128 mV dec−1, and a Pt mass activity of 0.11 A cm−2 mgPt−1 at 200 mV in the alkaline medium (1.0 M KOH solutions, pH = 14.0), which are substantially higher than the Pt(w/o-MI)/FTO and the commercially available Pt-loaded carbon (Pt/C) on the FTO cathodes. The mechanism of the efficient HER for the Pt(w-MI)/FTO cathode was investigated by an electrochemical impedance spectroscopic (EIS) method. The bulk charge transport in the Pt(w-MI) film is faster than that in the Pt(w/o-MI) film, ascribed to the compacted and well-connected Pt nanoparticles for Pt(w-MI). Furthermore, the surface proton reduction for Pt(w-MI) is also faster than that for Pt(w/o-MI), affording the efficient HER activity for Pt(w-MI) compared to Pt(w/o-MI).