Tin-doped Indium Oxide Electrodes Research Articles

Modulating indium doped tin oxide electrode properties for laccase electron transfer enhancement

Indium doped tin oxide (ITO) electrodes were functionalized with gold nanoparticles (GNPs) and cysteamine monolayer to enhance the heterogeneous electron transfer process of laccase from Trametes versicolor. The assembly of GNP on ITO support was performed through generation of H+ species at the electrode surface by hydroquinone electrooxidation at 0.9V vs Ag/AgCl. Uniform distribution of gold nanoparticle aggregates on electrode surfaces was confirmed by atomic force microscopy. The size of GNP aggregates was in the range of 200–500nm. The enhanced charge transfer at the GNP functionalized ITO electrodes was observed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy. Electrocatalytic behavior of laccase immobilized on ITO modified electrode toward oxygen reduction reaction was evaluated using CV in the presence of 2,2′-azino-bis 3-ethylbenzothiazoline-6-sulfuric acid (ABTS). The obtained sigmoidal-shaped voltammograms for ABTS reduction in oxygen saturated buffer solution are characteristic for a catalytic process. The intensity of catalytic current increased linearly with mediator concentration up to 6.2×10−4M. The registered voltammogram in the absence of ABTS mediator clearly showed a significant faradaic current which is the evidence of the interfacial oxygen reduction.

Seed Layer-Assisted Chemical Bath Deposition of CuO Films on ITO-Coated Glass Substrates with Tunable Crystallinity and Morphology

A seed layer-assisted chemical bath deposition (SCBD) method has been developed to create high quality CuO thin films on transparent conductive electrode/glass substrates. A CuO seed layer is formed by the electrodeposition of Cu2O on a tin-doped indium oxide (ITO) electrode for 10 s, followed by a brief (15 min) heating step to convert the Cu2O to CuO. The seed layer is found to be essential for the growth of micrometer-thick, adherent CuO thin films on ITO-coated glass, as no films were observed to form on substrates without a seed layer. The addition of sodium lactate to the SCBD solution can be used to tune the morphology and relative crystallinity of the CuO films. A highly crystalline CuO film possessing a resistivity of 3.3 × 105 Ω·cm has been deposited from a solution without sodium lactate, while a largely amorphous CuO film grown from a solution with a lactate/copper molar ratio equal to 1.0 displayed a resistivity of 7.2 × 105 Ω·cm. The CuO film with greater amorphous character exhibited a significantly larger specific capacitance as a redox active electrode compared to the crystalline film (2700 mF/g vs 96 mF/g).

Immobilization of a Redox-active Catecholato Pt(II) Complex on an Indium-doped Tin Oxide Electrode via Phosphonate Anchors

Abstract The reaction of tetraethyl [2,3-dihydroxy-1,4-phenylenebis(methylene)]bisphosphonate (Et4LH2) with [PtCl2(DTBbpy)] (DTBbpy: 4,4′-di-tert-butyl-2,2′-bipyridine) afforded [Pt(Me4L)(DTBbpy)] (1), [Pt(Bn4L)(DTBbpy)] (2), Na2[Pt(Me2L)(DTBbpy)] (3), and [Pt(H4L)(DTBbpy)] (4) with tetramethyl-, tetrabenzyl-, half-protected, and fully-deprotected groups under different reaction conditions. The introduction of phosphonatomethyl groups at the 3,6-position of a redox-active catecholato unit led to slight shifts in charge-transfer bands and catecholato-centered redox processes in solution. The presence of deprotonated anchors in 3 resulted in the immobilization of the complex onto an indium-doped tin oxide electrode, demonstrating a well-defined redox response from the tethered complex.

Electrochemical detection of free glycerol in biodiesel using electrodes with single gold particles in highly ordered SiO2 cavities

In the present work, we report a direct electrochemical glycerol detection method using thermally annealed, facet-specific, single gold particles, Au (111), located in the cavities of a highly ordered SiO2 cavity array on an indium-doped tin oxide (ITO) electrode. We fabricated an interconnected array structure comprised of SiO2 cavities onto ITO electrodes via monolayer colloidal crustal (MCC) templates. Gold nanoparticles (Au NPs) were electrodeposited at the bottom of the SiO2 cavities in direct contact with the ITO electrodes (Au (poly)/SiO2 cavity/ITO electrode). Upon annealing the electrodes at 700°C, single gold particles were formed, dominated by the (111) facet (Au (111)/SiO2 cavity/ITO electrode). The Au (111)/SiO2 cavity/ITO electrode exhibited satisfactory electrocatalytic activity to the oxidation of glycerol. More importantly, each cavity of the SiO2 possibly behaves as an independent electrochemical cell in which the glycerol molecules are trapped; this produces a microenvironment advantageous to catalyze electrooxidation. Moreover, Au (111)/SiO2 cavity/ITO electrode design gave a wide linear range from 0.01mM to 0.8mM, and a low detection limit of 1.49μM. As a glycerol sensor, the electrode displayed good reproducibility and long-term stability. The electrode was applied to directly determine the free glycerol in the biodiesel samples. This strategy might provide an approach to study electrochemical reactions on single particles in a microenvironment and offers a method for constructing alcohols sensors.

A dual-plate ITO–ITO generator–collector microtrench sensor: surface activation, spatial separation and suppression of irreversible oxygen and ascorbate interference

Generator-collector electrode systems are based on two independent working electrodes with overlapping diffusion fields where chemically reversible redox processes (oxidation and reduction) are coupled to give amplified current signals. A generator-collector trench electrode system prepared from two tin-doped indium oxide (ITO) electrodes placed vis-à-vis with a 22 μm inter-electrode gap is employed here as a sensor in aqueous media. The reversible 2-electron anthraquinone-2-sulfonate redox system is demonstrated to give well-defined collector responses even in the presence of oxygen due to the irreversible nature of the oxygen reduction. For the oxidation of dopamine on ITO, novel "Piranha-activation" effects are observed and chemically reversible generator-collector feedback conditions are achieved at pH 7, by selecting a more negative collector potential, again eliminating possible oxygen interference. Finally, dopamine oxidation in the presence of ascorbate is demonstrated with the irreversible oxidation of ascorbate at the "mouth" of the trench electrode and chemically reversible oxidation of dopamine in the trench "interior". This spatial separation of chemically reversible and irreversible processes within and outside the trench is discussed as a potential in situ microscale sensing and separation tool.

Efficiency Enhancement of Inverted Polymer Solar Cells Using Ionic Liquid-functionalized Carbon Nanoparticles-modified ZnO as Electron Selective Layer

Abstract ZnO thin film was fabricated on tin-doped indium oxide electrode as an electron selective layer of inverted polymer solar cells using magnetron sputtering deposition. Ionic liquid-functionalized carbon nanoparticles (ILCNs) film was further deposited onto ZnO surfaces by drop-casting ILCNs solution to improve interface properties. The power conversion efficiency (PCE) of inverted polymer solar cells (PSCs) with only ZnO layer was quickly decreased from 2.7% to 2.2% when the thickness of ZnO layer was increased from 15 nm to 60 nm. However, the average PCE of inverted PSCs with ZnO layer modified with ILCNs only decreased from 3.5% to 3.4%, which is comparable to that of traditional PSCs with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) anode buffer layer. The results suggested that the contact barrier between ZnO layer and poly(3-hexylthiophene) and phenyl-C61-butyric acid methylester (P3HT:PCBM) blended film compared to ZnO bulk resistance can more significantly influence the performance of inverted PSCs with sputtered ZnO layer. The vanishment of negative capacitive behavior of inverted PSCs with ILCNs modified ZnO layer indicated ILCNs can greatly decrease the contact barrier of ZnO/P3HT:PCBM interface.

“Roll-on” nano-CIGSe film electrodes in photo-hydrogenation

Commercial nano-CIGSe powder (nominal CuIn0.7Ga0.3Se2, average particle size < 100 nm) is applied to tin-doped indium oxide (ITO) electrodes in a simple “roll-on” process from n-hexanol to give thin photo-electrochemically active films. Films “as deposited” and “annealed” in selenium atmosphere at 350 °C are compared with the latter performing substantially better. Perhaps surprisingly, photo-transient voltammetry suggests only insignificant effects when changing aqueous electrolyte from Eu(NO3)3 to KNO3 or when changing electrolyte concentration, most likely due to a dominating electron-quenching process caused by dissolved dioxygen. However, when under inert argon atmosphere, generator-collector photo-transient voltammetry with a 50 μm Pt collector microelectrode placed close to the CIGSe film surface proves photo-induced H2 formation in 0.1 M KNO3 or in 0.1 M HNO3 (and it confirms electron-quenching by O2 in the presence of air). In aqueous 0.1 M HNO3 effective electron-quenching (photo-hydrogenation) with fumaric acid is observed with current yields of ca. 60% for fumarate to succinate conversion. Detrimental loss of photoelectrochemical activity (probably via photo-corrosion) with time occurs.

Work function tuning of tin-doped indium oxide electrodes with solution-processed lithium fluoride

Solution-processed lithium fluoride (sol-LiF) nanoparticles synthesized in polymeric micelle nanoreactors enabled tuning of the surface work function of tin-doped indium oxide (ITO) films. The micelle reactors provided the means for controlling surface coverage by progressively building up the interlayer through alternating deposition and plasma etch removal of the polymer. In order to determine the surface coverage and average interparticle distance, spatial point pattern analysis was applied to scanning electron microscope images of the nanoparticle dispersions. The work function of the sol-LiF modified ITO, obtained from photoelectron emission yield spectroscopy analysis, was shown to increase with surface coverage of the sol-LiF particles, suggesting a lateral depolarization effect. Analysis of the photoelectron emission energy distribution in the near threshold region revealed the contribution of surface states for surface coverage in excess of 14.1%. Optimization of the interfacial barrier was achieved through contributions from both work function modification and surface states.

Influence of ITO Electrode Surface Composition on the Growth and Optoelectronic Properties of Electrodeposited Cu2O Thin Films

Morphological inhomogeneity between electrodeposited cuprous oxide (Cu2O) thin films on nominally equivalent tin-doped indium oxide (ITO) electrodes under identical deposition conditions is reported. Dependence of the Cu2O photocurrent generation ability on thin-film morphology is also described. Films exhibiting compact, polyhedral crystallites produce short circuit photocurrents more than 10 times greater than those consisting of sparse, dendritic crystallites. A correlation between the ITO surface stoichiometry and the resulting Cu2O film morphology is established using X-ray photoelectron spectroscopy for identification of the ITO electrode surface chemical states. Variation in the Sn/In atomic ratio up to 33% is measured at the surfaces of ITO substrates from the same supplier lot, highlighting the importance of thorough electrode characterization prior to electrodeposition to obtain repeatable Cu2O performance for energy conversion applications.

Electrocatalytic oxidation of alcohols on single gold particles in highly ordered SiO2 cavities

In the present work, we report a new and simple approach for preparing a highly ordered Au (111) nanoparticle (NP) array in SiO2 cavities on indium-doped tin oxide (ITO) electrodes. We fabricated a SiO2 cavity array on the surface of an ITO electrode using highly ordered self-assembly of polystyrene spheres as a template. Gold NPs were electrodeposited at the bottom of the SiO2 cavities, and single gold NPs dominated with (111) facets were generated in each cavity by annealing the electrode at a high temperature. Such (111) facets were the predominate trait of the single gold particle which exhibited considerable electrocatalytic activity toward oxidation of methanol, ethanol, and glycerol. This has been attributed to the formation of incipient hydrous oxides at unusually low potential on the specific (111) facet of the gold particles. Moreover, each cavity of the SiO2 possibly behaves as an independent electrochemical cell in which the methanol molecules are trapped; this produces an environment advantageous to catalyzing electrooxidation. The oxidation of methanol on the electrodes is a mixed control mechanism (both by diffusion and electrode kinetics). This strategy both provided an approach to study electrochemical reactions on a single particle in a microenvironment and may supply a way to construct alcohols sensors.

Electrodeposition of Well-Adhered Multifarious Au Particles at a Solid|Toluene|Aqueous Electrolyte Three-Phase Junction

In order to obtain uniform and reproducible surface enhanced Raman spectroscopy (SERS) platforms, a novel method for deposition of well-adhered multifarious gold particles on a tin-doped indium oxide electrode through electrogeneration at an electrode|gold compound in toluene|aqueous-electrolyte three-phase junction was developed. The electrodeposition was carried out both by double-potential-step chronoamperometry with one pulse for nucleation and one for growth of the particles, and by potentiostatic single-potential-step chronoamperometry. Both procedures give angular, multifarious Au particles with a diameter of 150 ± 40 nm. The size of the particles is independent of deposition time, after an initial growth phase, and controlled by the formation of a microemulsion at the three-phase junction. The particles are likely deposited from the microdroplets and their size is determined by the amount of gold salt in a droplet. The mechanism involves electoreduction of tetraoctylammonium tetrachloroaurate at t...

Generator–collector electroanalysis at tin-doped indium oxide–epoxy–tin-doped indium oxide junction electrodes

Generator–collector electroanalysis approaching the nanomolar level is demonstrated for the reduction of Ru(NH3)63+ in aqueous (NH4)2SO4 (saturated, as a naturally low-oxygen electrolyte medium) and at tin-doped indium oxide (ITO) electrodes. ITO–ITO double band and double plate geometries are compared. Cyclic voltammetric detection down into the sub-micromolar concentration level is readily achieved at co-planar ITO–ITO double plate junction electrodes with typically 4μm inter-electrode gap, 5mm length, and ca. 62μm average inter-electrode trench depth. Trace oxygen (ca. 60μM) is shown to enhance both generator and collector currents and the cathodic excess current |Igenerator|−|Icollector| is employed to estimate the bimolecular rate constant for Ru(NH3)62+ reacting with O2, k2=104mol−1dm3s−1.

Ultrasensitive electrochemical immunosensor for HE4 based on rolling circle amplification

A novel electrochemical immunoassay system for the detection of human epididymis-specific protein 4 (HE4) was developed. A chitosan–titanium carbide (TiC) nanocomposition film was first electrodeposited onto a tin-doped indium oxide (ITO) electrode at a constant potential. Gold (Au) nanoparticles were then electrodeposited on the surface of the chitosan–TiC film by cyclic voltammetry (CV). The capture antibody (anti-HE4) was adsorbed onto the Au and TiC nanoparticles. After a specific sandwich immunoreaction among the capture antibody, HE4, and biotinylated secondary antibody, biotinylated primer DNA was immobilized on the secondary antibody by biotin–streptavidin system. Appropriate amounts of circular template DNA and biotinylated primer DNA were used for rolling circle amplification (RCA) under optimal conditions. The RCA products provided a large number of sites to link DNA detection probes. Doxorubicin hydrochloride intercalated the CG–GC steps between the RCA products and the DNA detection probes, which was monitored by differential pulse voltammetry (DPV) based on the current signal of doxorubicin hydrochloride. With the above-mentioned amplification factors, the current responded to HE4 linearly in the concentration range of 3–300pM under optimal detection conditions, with a detection limit of 0.06pM. Stepwise changes in the microscopic features of the surfaces and electrochemical properties upon the formation of each layer were confirmed by scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS). This system was successfully employed for the detection of HE4 with good accuracy and renewable ability.

Self-Assembly and Orientation of Hydrogen-Bonded Oligothiophene Polymorphs at Liquid–Membrane–Liquid Interfaces

One of the challenges in organic systems with semiconducting function is the achievement of molecular orientation over large scales. We report here on the use of self-assembly kinetics to control long-range orientation of a quarterthiophene derivative designed to combine intermolecular π-π stacking and hydrogen bonding among amide groups. Assembly of these molecules in the solution phase is prevented by the hydrogen-bond-accepting solvent tetrahydrofuran, whereas formation of H-aggregates is facilitated in toluene. Rapid evaporation of solvent in a solution of the quarterthiophene in a 2:1:1 mixture of 1,4-dioxane/tetrahydrofuran/toluene leads to self-assembly of kinetically trapped mats of bundled fibers. In great contrast, slow drying in a toluene atmosphere leads to the homogeneous nucleation and growth of ordered structures shaped as rhombohedra or hexagonal prisms depending on concentration. Furthermore, exceedingly slow delivery of toluene from a high molecular weight polymer solution into the system through a porous aluminum oxide membrane results in the growth of highly oriented hexagonal prisms perpendicular to the interface. The amide groups of the compound likely adsorb onto the polar aluminum oxide surface and direct the self-assembly pathway toward heterogeneous nucleation and growth to form hexagonal prisms. We propose that the oriented prismatic polymorph results from the synergy of surface interactions rooted in hydrogen bonding on the solid membrane and the slow kinetics of self-assembly. These observations demonstrate how self-assembly conditions can be used to guide the supramolecular energy landscape to generate vastly different structures. These fundamental principles allowed us to grow oriented prismatic assemblies on transparent indium-doped tin oxide electrodes, which are of interest in organic electronics.

Mediatorless bioelectrocatalysis of dioxygen reduction at indium-doped tin oxide (ITO) and ITO nanoparticulate film electrodes

Bilirubin oxidase was immobilised on ITO electrodes: bare or covered by ITO nanoparticulate film. The latter material was obtained by immersion and withdrawal of the substrate into ITO nanoparticles suspension. Formation of a protein deposit was confirmed by scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The electrode surface is covered by a protein film in the form of globular aggregates and it exhibits mediatorless electrocatalytic activity towards dioxygen reduction to water at pH 4.8. Modification of the electrode with ITO particles increases its catalytic activity about ten times up to 110 μA cm −2 seen for electrodes prepared by twelve immersion and withdrawal steps into ITO nanoparticle suspension. The catalytic activity is almost unaffected by addition of mediator to solution. The stability of the electrodes is increased by cross-linking of the enzyme with bovine serum albumin and glutaraldehyde. This electrode was applied as biocathode in a zinc–dioxygen battery operating in 0.1 mol dm −3 McIlvaine buffer (pH 4.8).

New method for preparation of polyoxometalate-capped gold nanoparticles, and their assembly on an indium-doped tin oxide electrode

Functionalized gold nanoparticles capped with polyoxometalates were prepared by a simple photoreduction technique where phosphododecamolybdates serve as reducing reagents, photocatalysts, and as stabilizers. TEM images of the resulting gold nanoparticles show the particles to have a relative narrow size distribution. Monolayer and multilayer structures of the negatively charged capped gold nanoparticles were deposited on a poly(vinyl pyridine)-derivatized indium-doped tin oxide (ITO) electrode via the layer-by-layer technique. The surface plasmon resonance band of the gold nanoparticles displays a blue shift on the surface of the ITO electrode. This is due to the substrate-induced charge redistribution in the gold nanoparticles and a change in the electromagnetic coupling between the assembled nanoparticles. The modified electrode exhibits the characteristic electrochemical behavior of surface-confined phosphododecamolybdate and excellent electrocatalytic activity. The catalysis of the modified electrode towards the model compound iodate was systematically studied. The heterogeneous catalytic rate constant for the electrochemical reduction of iodate was determined by chronoamperometry to be ca. 1.34 × 105 mol−1·L·s−1. The amperometric method gave a linear range from 2.5 × 10−6 to 1.5 × 10−3 M and a detection limit of 1.0 × 10−6 M. We believe that the functionalized gold nanoparticles prepared by this photoreduction technique are advantageous in terms of fabrication of sensitive and stable redox electrodes.

One-step electrodeposition of carbon–silicate sponge assisted by a three-phase junction for efficient bioelectrocatalysis

Single-step electrodeposition of nanocomposite silicate materials based on hydrophilic carbon nanoparticles (CNPs) and a hydrophobic sol-gel precursor with the help of an electrode|organic-phase|aqueous-electrolyte three-phase junction is presented. A tin-doped indium oxide electrode is immersed into a cell filled with two immiscible liquids. The upper aqueous phase contains dispersed carbon nanoparticles in electrolyte and the bottom organic phase consists of sol-gel precursor in nitrobenzene. Applying a positive potential to the electrode results in generation of protons which act as catalyst for the sol-gel process. A 1625 ± 140 nm thick, sponge-like, nanoparticulate stripe of CNPs embedded in a silicate matrix is formed at the electrode surface close to the three-phase junction. The obtained material is an excellent support for enzyme adsorption exhibiting mediatorless bioelectrocatalysis of dioxygen reduction.

Optical and electrochemical properties of ordered macroporous gold array on the ITO surface

The electrochemical and optical properties of transparent, two-dimensional macroporous gold film were investigated. Colloidal crystal templates were assembled onto indium-doped tin oxide (ITO) glass surface through vertical depositing method. Following gold electrodeposition, they were removed by dissolution with tetrahydrofuran (THF). The highly ordered macroporous gold array was achieved. It was characterized by scanning electron microscope (SEM) and ultraviolet visible (UV–vis) spectrophotometry. The optical transparency of the gold film was near 25% and fairly constant between 300 and 900 nm. The macroporous gold film electrode was mounted into a thin-layer transmission cell. The electrochemical response was evaluated by thin-layer cyclic voltammograms (CV) of the Fe (CN) 6 3−/Fe (CN) 6 4− couple. Thin-layer cell exhibits good shape of waves and nearly symmetric cathodic and anodic waves. E 0′ value and n of TMPD + /TMPD (TMPD is acronyms for N,N,N′,N′-tetramethyl-p-phenylenediamine, and TMPD + is its mono-cation radical) couple were determined. Furthermore, results demonstrated electrolytic equilibrium was faster reached in macroporous gold film than ITO electrode.

Visible spectroelectrochemical characterization of Geobacter sulfurreducens biofilms on optically transparent indium tin oxide electrode

We report visible spectroelectrochemical (SEC) characterization of cytochrome c 552 (cyt c 552) in viable Geobacter sulfurreducens biofilms on tin-doped indium oxide (ITO) electrodes poised at 0.24 V vs. SHE. G. sulfurreducens biofilms were grown in minimal medium with acetate as electron donor (turnover conditions), followed by 24 h incubation in electron donor-depleted medium (non-turnover conditions). The electronic absorption spectra of G. sulfurreducens biofilms showed the lowest energy absorption band in the reduced state at 552 nm, which indicated excess of cyt c 552 in the biofilm. The spectra under non-turnover conditions displayed gradual reduction of the cyt c 552, following the step-wise decrease of electrode potential from 0.0 V to −0.6 V vs. standard calomel electrode (SCE). The spectral changes were fully reversible in both positive and negative direction of the scan potential, with average midpoint potential value of −0.42 V vs. SCE. Confocal microscopy analysis revealed that the thickness of biofilms under turnover conditions and non-turnover conditions was approximately 35 and 3.5 μm, respectively. This is the first study to observe the reversible redox conversion of cyt c 552 in viable G. sulfurreducens biofilms.

A rapid green route for fabricating efficient SERS substrates

This study develops a simple, rapid electrochemical approach for preparing dendrite-shaped Ag nanomaterials, which are well known as effective SERS substrates. In addition to yielding silver that exhibits a strong enhancement in SERS measurements when tested with 2,2′-dithiodipyridine and ethylenethiourea, this new fabrication method does not require any template, surfactants or supporting electrolyte, making it environment friendly. Analysis illustrates that the as-prepared Ag products are essentially pure silver consisting of abundant {111}-oriented crystallites. These Ag dendrites formed on a commercially available tin-doped indium oxide electrode could also be easily transferred onto other desired surfaces, making their application in SERS measurements more versatile.