Enhanced electrochromic performance of macroporous WO3 films formed by anodic oxidation of DC-sputtered tungsten layers

Self-organized macroporous tungsten trioxide (WO₃) films are obtained by anodic oxidation of DC-sputtered tungsten (W) layers on 10 mm × 25 mm indium tin oxide (ITO)-coated glass. Under optimized experimental conditions, uniformly macroporous WO₃ films with a thickness of ca. 350 nm are formed. The film shows a connected network with average pore size of 100 nm and a pore wall thickness of approximately 30 nm. The anodized film becomes transparent after annealing without significant change in macroporous structure. In 0.1 M H₂SO₄, the macroporous WO₃ films show enhanced electrochromic properties with a coloration efficiency of 58 cm² C⁻¹. Large modulation of transmittance (∼50% at 632.8 nm) and a switching speed of about 8 s are also achieved with this macroporous film.     

Electrochromic properties of porous NiO thin film as a counter electrode for NiO/WO3 complementary electrochromic window

Highly porous nickel oxide (NiO) thin films were prepared on ITO glass by chemical bath deposition (CBD) method. SEM results show that the as-deposited NiO film is constructed by many interconnected nanoflakes with a thickness of about 20 nm. The electrochromic properties of the NiO film were investigated in a nonaqueous LiClO₄–PC electrolyte by means of optical transmittance, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The NiO film exhibits a noticeable electrochromic performance with a variation of transmittance up to 38.6% at 550 nm. The CV and EIS measurements reveal that the NiO film has high electrochemical reaction activity and reversibility due to its highly porous structure. The electrochromic (EC) window based on complementary WO₃/NiO structure shows an optical modulation of 83.7% at 550 nm, much higher than that of single WO₃ film (65.5% at 550 nm). The response time of the EC widow is found to be about 1.76 s for coloration and 1.54 s for bleaching, respectively. These advantages such as large optical modulation, fast switch speed and excellent cycle durability make it attractive for a practical application.     

Redox and catalytic properties of new polypyrrole modified electrodes functionalized by [Ru(bpea)(bpy)H2O] complexes; bpea=N,N′-bis(2-pyridylmethyl)ethylamine, bpy=2,2′-bipyridine

New ruthenium(II) complexes containing one or two pyrrole-functionalized polypyridylic ligands have been prepared in order to study their electrochemical behaviour in heterogeneous phase, after anodic polymerization from CH₂Cl₂ solution on an electrode surface. Complexes containing one pyrrole unit have general formula [Ru(bpea-pyr)(bpy)(L)]²⁺ (bpea-pyr=N-[3-bis(2-pyridylmethyl)aminopropyl]pyrrole, bpy=2,2′-bipyridine, L=Cl, complex 3, or L=H₂O, complex 1), whereas compounds having two pyrrole units correspond to [Ru(bpea-pyr)(bpy-pyr)(L)]²⁺ (bpy-pyr=4-methyl-4′-pyrrolylbutyl-2,2′-bipyridine, L=Cl, complex 4, or L=H₂O, complex 2). Upon oxidative polymerization, all complexes form highly stable polypyrrolic films on a graphite disk electrode surface. An electrode modified with complex 2 polypyrrole coating film, C/poly-2, has been tested as heterogeneous catalyst for the oxidation of benzyl alcohol, showing a remarkably high efficiency and notably improving the results obtained with analogous complexes in homogeneous phase.     

Structural characterisation of rac-bis(2,2-bipyridine)(2,5-dipyridylpyrazine)ruthenium(II) hexafluorophosphate; a key building block for metallodendrimers

The complex [(bipy)₂Ru(dpp)][PF₆]₂ which contains a vacant 2,2^′-bipyridine-like metal-binding domain has been structurally characterised. This compound is a key building block for the construction of metallodendrimers using the “complexes as metals, complexes as ligands” approach.     

A new three-dimensional ruthenium(II) complex via hydrogen bonds: Ru(bpy)2(ox)·4H2O (bpy=2,2′-bipyridine, ox=oxalate ion)

A hydrogen-bonded complex Ru(bpy)₂(OX)·4H₂O has been synthesized. Its structure consists of a unique three-dimensional network in which Ru(bpy)₂(OX)·4H₂O units are alternatively linked by tetracyclic and octacyclic rings. The cyclic voltammogram of the titled compound has been studied.     

EUROCAT oxide: an European V2O5–WO3/TiO2 SCR standard catalyst study: Characterisation by electron microscopies (SEM, HRTEM, EDX) and by atomic force microscopy

The morphology and the homogeneity in chemical compositions of fresh and used V₂O₅–WO₃/TiO₂ EUROCAT SCR samples, in their original monolith form and after gentle grinding, have been investigated by means of electron microscopies and EDX analyses. It appears clearly that the monoliths were constituted of fibres rich in Si, Al and Ca embedded without preferential orientation in a nearly homogeneous oxide phase containing Ti, V, and W. This phase was in the form of small particles of homogeneous size of around 20–40 nm. The used catalyst was very similar to the fresh one, only the presence of S element and of more defects and more fibres were observed on the surface of the monolith. This observation was confirmed by a higher roughness detected using AFM technique.

EDX–TEM studies on the powders obtained by gently grinding the monoliths have shown that W and V species were well distributed in TiO₂ support and that the repartition of the W species, very homogeneous in the fresh sample, became somewhat slightly more heterogeneous in the used sample. V species were not so well dispersed that W species and even, some particles rich in V were observed on the used sample. This may be due to the migration and agglomeration of some of the V species. More particles, very rich in Si, were also observed for the used sample suggesting that the coating of the fibres by the active phase was partly deteriorated during SCR reaction. This observation was supported by an AFM analysis which showed a higher surface roughness for the used sample.

It was also observed by high resolution TEM that the first one or two atomic layers at the surface of all crystallites appear amorphous, while the further layers are well crystallised with the anatase structure. For the used sample this amorphous layer is slighly larger. This is an important feature for electrical conductivity (mainly at the surface) and catalytic properties.     

Electrochemically prepared polymer solar cell by three-layer deposition of poly(3,4-ethylenedioxythiophene)/poly(2,2′-bithiophene)/fullerene (PEDOT/PBT/C60)

A new electrochemical approach to fabricate polymer solar cell has been developed. Electropolymerization of 2,2′-bithiophene was done on top of the electrodeposited p-doped PEDOT layer. Fullerene was deposited as a third layer after initiating n-doping of the polymers. Composition and oxidation states of the polymers were monitored by UV-Vis-NIR spectroscopy. Morphological changes were followed with Atomic Force Microscopy (ATM) revealing rough nanostructures of the layers. The composition and performance of the solar cells were compared to the cells fabricated by using conventional spin-coating technique. Photoresponse with the maximum V_oc of 0.47 V and the highest J_sc of 0.55 mA/cm² was measured.     

Electrochemical lithium insertion in (PO2)4(WO3)2m (2 ≤ m ≤ 10): Relation among the electrochemical insertion process and structural features

In this work it is presented a review of the main results obtained during the electrochemical lithium insertion in the family of monophosphate tungsten bronzes (PO₂)₄(WO₃)_2m (2 ≤ m ≤ 10). This family of oxides is a good system in order to study the relation among the electrochemical processes observed in the course of lithium insertion and the changes of bronzes structures. By means of X-ray diffraction experiments, the nature of Li_x(PO₂)₄(WO₃)_2m phases has been elucidated and a correlation with the reversible/irreversible processes observed during the electrochemical insertion has been established. The electrical properties of the inserted Li_x(PO₂)₄(WO₃)_2m phases were measured and a relation with the amount of lithium inserted and m was also found.     

EQCM study of the ECL quenching of the tris(2,2′-bipyridyl)ruthenium(II)/tris-n-propylamine system at a Au electrode in the presence of chloride ions

Significant effect of chloride ions on the electrogenerated chemiluminescence (ECL) behavior of the ruthenium(II)tris(2,2′-bipyridine) (Ru(bpy)₃²⁺)/tri-n-propylamine (TPrA) system at a Au electrode was reported. At low concentrations (e.g., [Cl⁻] < 5 mM), the ECL was enhanced; at relatively high concentrations, however, the ECL intensity decreased with the increase of the [Cl⁻]. At [Cl⁻] = 90 mM, ∼50% and 100% ECL inhibition was observed for the first and the second ECL wave, respectively. The electrogenerated gold-chloride complexes (AuCl₂⁻ and AuCl₄⁻) which were verified using an electrochemical quartz-crystal microbalance (EQCM) method were found to be responsible for the ECL inhibition. This study suggests that care must be taken when a Au working electrode is used for ECL studies in chloride-containing buffer solutions (widely used in DNA probes) and/or with the commonly used chloride-containing reference electrodes since in these cases the ECL behavior may significantly disagree with that obtained using other electrodes and reaction media.     

Effect of [Mn(acac)3] and its combination with 2,2′-bipyridine on the autoxidation and oligomerisation of ethyl linoleate

In this study we investigated the autoxidation and oligomerisation of ethyl linoleate (EL) catalysed by [Mn(III)(acac)₃] (acac=2,4-pentanedionate) and its combination with 2,2-bipyridine (bpy), in comparison with the EL catalysed by Co(II) 2-ethylhexanoate (Co-EH). EL is a model compound for the alkyd resin in alkyd paints, Co-EH is a common drying catalyst for alkyd paints, and [Mn(acac)₃] and the [Mn(acac)₃]/bpy combination are potential new drying catalysts. The autoxidation of EL was studied through time-resolved Raman spectroscopy, oxygen uptake measurements, and peroxide amount determination. To follow the oligomerisation of EL in time, size exclusion chromatography was used. Head-space GC-MS measurements were performed to determine the amounts of hexanal and pentanal that were formed as volatile byproducts during the autoxidation of EL. The autoxidation rates of EL in the presence of Co-EH and [Mn(acac)₃]/bpy were found to be similar, while the rate in the presence of [Mn(acac)₃] was slower. The extent of EL oligomerisation was much higher for [Mn(acac)₃] compared to the other catalysts. Different mechanisms are proposed for the mode of action for each of the catalysts: Co-EH is primarily a hydroperoxide decomposition catalyst, as is [Mn(acac)₃], only less active. The [Mn(acac)₃]/bpy combination probably forms the very reactive complexes [Mn(III)(acac)₂(bpy)]⁺ and [Mn(II)(acac)₂(bpy)], which are responsible for a very high autoxidation rate, but also for significant degradation of the formed EL oligomers via β-scission reactions due to the promotion of alkoxy radical formation.     

Layer-by-layer self-assembled nanostructured phthalocyaninatoiron(II)/SWCNT-poly(m-aminobenzenesulfonic acid) hybrid system on gold surface: Electron transfer dynamics and amplification of H2O2 response

The fabrication of nanostructured platform of poly(m-aminobenzenesulfonic acid) functionalised single-walled carbon nanotubes (SWCNTs-PABS)-iron(II)phthalocyanine nanoparticles (nanoFePc) using layer-by-layer(LBL) self-assembly strategy is described. The substrate build-up, via strong electrostatic interaction, was monitored using atomic force microscopy (AFM) and electrochemical measurements. As the number of bilayers is increased, the electron transfer kinetics of the ferricyaninde/ferrocyanide redox probe is decreased, while the electrochemical reduction of H₂O₂ at a constant concentration is amplified. The amplification of the electrochemical response to H₂O₂ detection suggests that this type of electrode could provide an important nano-architectural sensing platform for the development of a sensor.     

New Cu(I) complexes with 2,2′-biquinolyl and 2,2′-quinolyl-pyridine containing polymer ligands as electrocatalysts for O2 activation in the oxidation of aliphatic amines

A series of polynuclear Cu(I) complexes with various types of polymer ligands containing 2,2′-biquinolyl (biQ) or 2,2′-quinolyl-pyridine (QPy) fragments in the polymer backbone was synthesized using sacrificial Cu anode. Cyclic voltammetry investigation of the obtained complexes revealed the formation of two types of Cu(I) coordination units, depending on the polymer's structure and electrolysis conditions. The first type of complexes, with only one biQ ligand per Cu(I) center, showed high oxidase activity in the air oxidation of primary and secondary amines to corresponding aldehydes with concomitant reduction of molecular oxygen to water. The reactions proceed in acetonitrile or N-methylpyrrolidone in the presence of O₂ at a potential of Cu^II/Cu^I electroreduction (−0.55 V vs. Ag/AgCl/KCl) with the high preparative yield and current efficiency. The possible scheme of the electrocatalytic process is discussed.     

Cobalt(II) porphyrin complex immobilized on the binary oxide SiO2/Sb2O3: electrochemical properties and dissolved oxygen reduction study

In this work, SiO₂/Sb₂O₃ prepared by the sol-gel processing method, having a specific surface area, S_BET, of 790 m² g⁻¹, an average pore diameter of 1.9 nm and 4.7 wt.% of Sb, was used as substrate base for immobilization of the 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine ion. Cobalt(II) ion was inserted into the porphyrin ring with a yield of complex bonded to the substrate surface of 59.4 μ mol g⁻¹. A carbon paste electrode of this material was used to study, by linear sweeping voltammetric and chronoamperometric techniques, the electrocatalytic reduction of dissolved oxygen. The reduction, at the electrode solid-solution interface, occurred at −0.25 V versus SCE in 1.0 mol l⁻¹ KCl solution, pH 5.5, by a four electron mechanism. The electrode response was invariant under various oxidation-reduction cycles showing that the system is chemically very stable. Such characteristics allowed the study of the electrode response towards various dissolved oxygen concentrations using the chronoamperometry technique. The cathodic peak current intensities plotted against O₂ concentrations, between 1.0 and 12.8 mg l⁻¹, showed a linear correlation. The electrode response time was very fast, i.e. about 1 s. This study was extended using the electrode to determine the concentration of dissolved oxygen in sea water samples.     

Effects of specific adsorption of copper (II) ion on charge transfer reaction at the thin film LiMn2O4 electrode/aqueous electrolyte interface

This study investigated the effect of a specific adsorption ion, copper (II) ion, on the kinetics of the charge transfer reaction at a LiMn₂O₄ thin film electrode/aqueous solution (1 mol dm⁻³ LiNO₃) interface. The zeta potential of LiMn₂O₄ particles showed a negative value in 1 × 10⁻² mol dm⁻³ LiNO₃ aqueous solution, while it was measured as positive in the presence of 1 × 10⁻² mol dm⁻³ Cu(NO₃)₂ in the solution. The presence of copper (II) ions in the solution increased the charge transfer resistance, and CV measurement revealed that the lithium insertion/extraction reaction was retarded by the presence of small amount of copper (II) ions. The activation energy for the charge transfer reaction in the solution with Cu(NO₃)₂ was estimated to be 35 kJ mol⁻¹, which was ca. 10 kJ mol⁻¹ larger than that observed in the solution without Cu(NO₃)₂. These results suggest that the interaction between the lithium ion and electrode surface is a factor in the kinetics of charge transfer reaction.     

Bis(4′-phenyl-2,2′:6′,2″-terpyridine)ruthenium(II): Holding the {Ru(tpy)2} embraces at bay

The solid state structure of [Ru(Phtpy)₂][PF₆]₂ · 4MeCN has been determined (Phtpy = 4′-phenyl-2,2′:6′,2″-terpyridine); [Ru(Phtpy)₂]²⁺ cations pack into sheets by virtue of {M(tpy)₂}₂ embraces, and the MeCN solvent molecules are involved in NH–C interactions which prevent the efficient packing of adjacent sheets. Comparisons with related structures lead to some generalizations about packing motifs in salts containing [M(Phtpy)₂]²⁺ or [M(pytpy)₂]²⁺ cations (pytpy = 4′-pyridyl-2,2′:6′,2″-terpyridine).     

DNA hybridization biosensor using chitosan–carbon nanotubes composite film as an immobilization platform and [Cu(bpy)(MBZ)2(H2O)] (bpy = 2,2′-bipyridine, MBZ = p-methylbenzoate) as a novel redox indicator

In this paper, a new DNA hybridization detection strategy was developed based on the immobilization of capture probe DNA on a chitosan (CS)–carbon nanotubes (CNTs) composite modified glassy carbon electrode (CS–CNTs/GCE) and the use of a copper complex, [Cu(bpy)(MBZ)₂(H₂O)] (bpy = 2,2′-bipyridine, MBZ = p-methylbenzoate), as a new redox hybridization indicator. The electrochemical characterization experiments showed that the nanocomposite film of CS–CNTs could effectively immobilize the capture probe DNA and greatly improve the electron-transfer reactions of the electroactive molecules. Electrochemical and fluorescent spectroscopic analysis revealed that the polypyridyl copper complex of [Cu(bpy)(MBZ)₂(H₂O)] bound to DNA via a typical intercalation mode. Surface studies further showed that the copper complex can discriminate between double-stranded and single-stranded DNA that immobilized on the surface of CS–CNTs/GCE. When being utilized as a redox indicator for the detection of hybridization for short DNA species related to phosphinothricin acetyltransferase (PAT), the indicator showed good specificity for recognizing the complementary, three-base mismatched and non-complementary DNA. Under the optimized conditions, the oxidation peak currents of the copper complex enhanced linearly with increases in the concentration of the complementary sequence in the range from 5.0 × 10⁻¹⁰ to 1.0 × 10⁻⁸ M. A detection limit of 5.0 × 10⁻¹⁰ M was also obtained based on the constructed DNA biosensor.     

Electrical properties of V2O5–WO3/TiO2 EUROCAT catalysts evidence for redox process in selective catalytic reduction (SCR) deNOx reaction

Electrical conductivity measurements on EUROCAT V₂O₅–WO₃/TiO₂ catalyst and on its precursor without vanadia were performed at 300°C under pure oxygen to characterize the samples, under NO and under NH₃ to determine the mode of reactivity of these reactants and under two reaction mixtures ((i) 2000 ppm NO + 2000 ppm NH₃ without O₂, and (ii) 2000 ppm NO + 2000 ppm NH₃ + 500 ppm O₂) to put in evidence redox processes in SCR deNO_x reaction.It was first demonstrated that titania support contains certain amounts of dissolved W⁶⁺ and V⁵⁺ ions, whose dissolution in the lattice of titania creates an n-type doping effect. Electrical conductivity revealed that the so-called reference pure titania monolith was highly doped by heterovalent cations whose valency was higher than +4. Subsequent chemical analyses revealed that so-called pure titania reference catalyst was actually the WO₃/TiO₂ precursor of V₂O₅–WO₃/TiO₂ EUROCAT catalyst. It contained an average amount of 0.37 at.% W⁶⁺dissolved in titania, i.e. 1.07 × 10²⁰ W⁶⁺ cations dissolved/cm³ of titania. For the fresh catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved in titania were found to be equal to 1.07 × 10²⁰ and 4.47 × 10²⁰ cm⁻³, respectively. For the used catalyst, the mean amounts of W⁶⁺ and V⁵⁺ ions dissolved were found to be equal to 1.07 × 10²⁰ and 7.42 × 10²⁰ cm⁻³, respectively. Since fresh and used catalysts have similar compositions and similar catalytic behaviours, the only manifestation of ageing was a supplementary progressive dissolution of 2.9 × 10²⁰ additional V⁵⁺ cations in titania.After a prompt removal of oxygen, it appeared that NO alone has an electron acceptor character, linked to its possible ionosorption as NO⁻ and to the filling of anionic vacancies, mostly present on vanadia. Ammonia had a strong reducing behaviour with the formation of singly ionized vacancies. A subsequent introduction of NO indicated a donor character of this molecule, in opposition to its first adsorption. This was ascribed to its reaction with previously adsorbed ammonia strongly bound to acidic sites. Under NO + NH₃ reaction mixture in the absence of oxygen, the increase of electrical conductivity was ascribed to the formation of anionic vacancies, mainly on vanadia, created by dehydroxylation and dehydration of the surface. These anionic vacancies were initially subsequently filled by the oxygen atom of NO. N^o atoms, resulting from the dissociation of NO and from ammonia dehydrogenation, recombined into dinitrogen molecules. The reaction corresponded to

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. In the presence of oxygen, NO did not exhibit anymore its electron acceptor character, since the filling of anionic vacancies was performed by oxygen from the gas phase. NO reacted directly with ammonia strongly bound on acidic sites. A tentative redox mechanism was proposed for both cases.     

Supported dicopper(II) complex catalyst Cu2(II)(μ-Br)2/SiO2: synthesis, characterization and catalytic properties for synthesis of ethylene carbonate

A μ-Br-bridged dicopper(II) complex, namely [Cu₂(μ-Br)₂·6H₂O](ClO₄)₂, has been prepared by metal ion grafting. A supported complex catalyst Cu₂(II)(μ-Br)₂/SiO₂was prepared by modifying the silica surface with NaOEt and anchoring the dicopper(II) complex precursor on the surface of the support. The structure of the complex catalyst has been characterized by elemental analysis, IR spectra and UV–VIS diffusion reflection spectra. Obtained data were compared with published data of the complex. TPD-MS and TPD-IR investigations indicated that CO₂ and ethylene oxide (EO) can be chemisorbed on the surface of the catalyst reversibly in a bridged state and can be desorbed from the surface at 105 and 115 K, respectively. In the high temperature range of 450–573 K, another reversible absorption state for CO₂ was also discovered. For EO, however, a decomposition absorption state was found which gave the dissociated species of CH₄ and CO. TPSR-MS experiments have shown that CO₂ and EO reacted on the surface effectively in the range of 343–413 K. An in situ IR method has been used to study the reactivity of the reactants on the surface of the catalyst, and the target product ethylene carbonate (EC) was detected in the range of 333–413 K. Catalytic experiments indicated that the one-way yield of EC is greater than 8.0% and that the selectivity of EC is greater than 82%. A synergic cyclization reaction pathway is proposed to account for the observed products.     

Solvothermal synthesis of a novel mixed valence Cu(I)/Cu(II) complex containing sulphate, malate and 4,4-bipyridine, [CuCu2(mal)(SO4)(bpy)2 · H2O]n. Unique binding mode of the malate anion

The reaction of CuSO₄ · 5H₂O with 4,4^′-bipyridine and malic acid at 140 °C under solvothermal conditions afforded a mixed valence three-dimensional coordination polymer [Cu^ICu^II₂(mal)(SO₄)(bpy)₂ · H₂O]_n, (1). The building unit consists of a Cu²⁺-dimer in which copper centers are bridged by malate and sulphate anions. SO₄²⁻ anion further connects dimeric unit with the Cu¹⁺ center. Building units are linked by 4,4^′-bipyridine ligands to form double chains, that are interconnected into 3D network through additional sulphate bridge.