Initial Oxidation Potential Research Articles

Effects of fluorine atom numbers on electrochromic properties of the benzothiadiazole-based D-A polymers

In this work, two fluorinated D-π-A-π-D type monomers, F-EDOT and FF-EDOT, were facilely synthesized by donor-acceptor-donor method via Stille coupling reaction, with monofluorinated benzothiadiazole and difluorinated benzothiadiazole as the acceptor units and 3,4-ethylenedioxythiophene (EDOT) as the donor units. The electrochemical polymerization behavior of the fluorinated monomers, electrochemical and electrochromic properties of the corresponding fluorinated D-A polymers were compared to study the effects of different fluorine atom numbers on the optoelectronic properties of the monomers and their resultant D-A polymers. The results show that the introduction of more F atoms into the conjugated backbone increases the oxidation potential of monomers, both of them have low initial oxidation potential (0.65 V/0.70 V). As in the case of monomers, the substitution of more F atoms also leads to the decreased HOMO energy level of the polymers, thus leading to the increased band gap energy of P(FF-EDOT) (1.39 eV). This result can be attributed to the deviation of planarity and the reduced effective conjugate length. As prepared fluorinated D-A polymers also have good adhesion on the electrode surface, favorable redox activity, and outstanding redox stability (the redox activity of P(F-EDOT) remains 99 % after 1000 cycles). At the same time, the fluorinated D-A polymers also show distinguish electrochromic properties under various external potentials; both the optical contrast and coloration efficiency decreased with the increase of F atom numbers, and the corresponding response time increased. As a result, both the fluorinated D-A polymers show light green in the neutral state, P(F-EDOT) shows more obvious electrochromic performance in the near infrared region (optical contrast: 35.02 %, coloration efficiency: 159.94 cm2 C−1, and quick response time: 0.2 s), accompanied with excellent discoloration stability and optical memory effect. The study of novel fluorinated-based electrochromic materials further expands the selection of acceptor units and the application prospect of electrochromic materials.

Novel donor-acceptor-donor type electrochromic polymers based on 1,3-indandione modified triphenylamine derivatives as new acceptor units

Two donor (D)-acceptor (A)-donor (D) type of conjugated monomers, ITPA and ICTPA, consisted of 1H-indene-1,3(2H)-dione (IN)- or 2-(3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile (INCN)-substituted triphenylamine as the acceptor unit, were synthesized by Stille coupling reaction and Knovenagel condensation reaction, and their corresponding polymers (PITPA and PICTPA) were prepared by electrochemical polymerization. Both ITPA and ICTPA hade low initial oxidation potential of 0.70 V and 0.76 V, respectively, which was conducive to achieve high-quality polymer films. In comparison with FTPA which was not substituted by IN unit, ITPA and ICTPA exhibited the distinct red-shifted and dual absorption bands due to the stronger electron-withdrawing ability of IN and INIC units. Moreover, the electrochromic results demonstrated that PITPA possessed much higher optical contrast of 41 %, higher coloration efficiency (CE) of 445.5 cm2 C−1 at 1100 nm with extremely fast response time as low as 0.3 s, and a promising optical memory behavior compared with its counterpart without IN unit. These results suggested that the introduction of IN unit into triphenylamine could improve the electrochromic performance of the conjugated polymers and also provide a new strategy to develop novel and high-performance electrocheomic polymers.

Nitrated benzothiadiazole-based D-A electrochromic polymers with tunable spectral properties

Nitrated benzothiadiazole (BT) is the promising acceptor units in constructing D-A-D electrochromic polymers, but its researches in the electrochromic field was very limited so far. In this work, four kinds of nitrated polymer precursors (Th-NO2-BT, EDOT-NO2-BT, Th-2NO2-BT, and EDOT-2NO2-BT) were synthesized by Stille coupling reaction with EDOT and thiophene units as the end groups (electron donor units) and mono-nitrated benzothiadiazole and di-nitrated benzothiadiazole as the core groups (electron acceptor units). The chemical structure and optical properties of the precursor were investigated by means of 1H NMR, UV–vis absorption and fluorescence spectra; the corresponding mono-nitrated polymer films were obtained in CH2Cl2-Bu4NPF6 system by electrochemical deposition method. The optical band gap of di-nitrated polymer precursor is obviously larger than the corresponding mono-nitrated polymer precursor (both ultraviolet and fluorescence spectra are obviously blue-shifted), accompanied with the obvious increased initial oxidation potential. Due to the fluorescence quenching effect of -NO2 group, their absolute quantum yields are all very low (0.0006–0.015). The spectroelectrochemistry and electrochromic kinetics of mono-nitrated polymer films (P(Th-NO2-BT) and P(EDOT-NO2-BT)) were studied. It was found that P(EDOT-NO2-BT) can show better electrochromic performance than P(Th-NO2-BT), with dark green in the neutral state and more obvious electrochromic performance in the near-infrared region (optical contrast: 38.4 %, coloration efficiency: 129.1 cm2/C, and fast response time: 1.4 s). This systematically study about the effects of nitro substitution effect on the properties of D-A electrochromic polymers, which will further expand the selection of the new acceptor units and the application prospect of nitrated electrochromic materials.

Adjustable optoelectronic properties of triphenylamine-ethylenedioxythiophene based hybrid electrochromic polymer with different electron-donating substituents

Due to the good optoelectronic properties of triphenylamine (TPA) and its derivatives-based organic conjugated polymers, they have been widely used in various organic electronic devices. They are easy to lose electrons to form stable cationic free radicals with color change under electrochemical oxidation conditions. Therefore, TPA derivatives-based electrochromism materials have attracted the widely attentions of researchers. In this work, a series of TPA derivatives were successfully obtained by Stille coupling reactions, and their basic optical and electrical properties were investigated in detail. Their corresponding polymer films (P(TPA-EDOT), P(PhTPA-EDOT), and P(OCH3TPA-EDOT)) were also prepared on transparent ITO glass by electrodeposition method and their electrochromic properties were further studied. Due to the relatively strong electron donating ability of OCH3– group on the TPA unit, the intramolecular charge transfer peak of OCH3TPA-EDOT is obvious red-shifted and its initial oxidation potential is relatively low, which is beneficial for it to get high-quality electrochromic polymers. Electrochemical analysis shows that all these three polymer films show reversible redox reaction with excellent redox stability. Spectroelectrochemistry shows that all of them have good electrochromic properties and show multi-electrochromic behavior with strong color change. The dynamic study show that all these three polymers have relatively fast switching time (as low as 0.8 s), high coloration efficiency (up to 206.2 C−1 cm2) and obvious optical contrast change. Especially in the near infrared region, the optical contrast is relatively high (P(TPA-EDOT) is 45.3 % at 1100 nm, P(PPhTPA-EDOT) is 53.1 % at 1100 nm, and P(OCH3TPA-EDOT) is 57.2 % at 1100 nm). All these results show that the different substituents on the TPA unit have a certain influence on the resultant monomers’ optoelectronic performances, and they also can adjust the optical band gap of the corresponding polymers with different electrochromic properties.

Fabrication of long-term stable electrochromic device based on high-quality PEDOT film

As one of representative conducting polymers (CPs), poly(3,4-ethylenedioxythiophene) (PEDOT) possesses fascinating electrochromic properties and commercial applications, but it suffers from the poor cycling stability in the charge-discharge process. In this work, we adopted a dual-approach mode to prepare high-quality PEDOT film in boron trifluoride etherate (BFEE) system via reducing the initial oxidation potential (Eonset) of 3,4-ethylenedioxythiophene (EDOT) monomers to increasing the conjugation degree of PEDOT films and no requiring the addition of other supporting electrolytes to protect the initial structure of PEDOT films. The Eonset of EDOT monomers in BFEE system was only 0.5 V, which was much smaller than other systems reported (1.00–1.26 V). The obtained PEDOT film with porous structure showed remarkable stability with an electrochemical activity retention rate of 91.5% after 190,000 cycles, and that of its electrochromic device (ECD) was 94.23% after 41,000 s. During the redox process, ECD had three color transformations (brown red, cyan, and blue) and the oxidation time and the reduction time were 0.4 s and 1.2 s, respectively. The calculated CE value reached 120 cm2 C−1. All these results suggest that the dual-approach mode can significantly enhance the quality of PEDOT film and thus enhance its cycling stability. In addition to that, the dual-approach mode can provide an effective strategy for the design of highly stable CPs for fabricating long-term stable ECD.

Enhancing electrocatalytic methanol oxidation of Pd-Ir nanoalloy through electron-rich catalytic interface induced by incorporating phosphorus

Incorporating less expensive nonmetal phosphorus (P) into noble metal-based catalysts has become a developing strategy to enhance the catalytic performance of electrocatalysts for methanol electrooxidation reaction (MOR), attributing to the electronic and synergistic structure alteration mechanism. In the work, three-dimensional nitrogen-doped graphene anchoring ternary Pd-Ir-P nanoalloy catalyst (Pd7IrPx/NG) was prepared by co-reduction strategy. As a multi-electron system, elemental P adjusts the outer electron structure of Pd and diminishes the particle size of nanocomposites, which heightens the electrocatalytic activity effectively and accelerate MOR kinetics in alkaline medium. The study reveals that the electron effect and ligand effect induced by P atoms on the hydrophilic and electron-rich surface of Pd7Ir/NG and Pd7IrPx/NG samples can reduce the initial oxidation potential and peak potential of COads, showing significantly enhanced the anti-poisoning ability compared with commercial Pd/C as the benchmark. Meanwhile, the stability of Pd7IrPx/NG is significantly higher than that of commercial Pd/C. The facile synthetic approach provides an economic option and a new vision for the development of electrocatalysts in MOR.

Carbonyl compounds and inorganic Brønsted acids as catalysts for electropolymerization of conductive polymers

For the electropolymerization of various conductive polymers, boron trifluoride diethyl etherate is commonly used as solvent to grant mild polymerization conditions – although it easily decomposes and leads to film qualities with low reproducibility. By using an appropriate catalyst, films with improved properties can be deposited at lower potentials from stable solvents in a reproducible manner. In this communication, various carbonyl compounds and inorganic Brønsted acids were investigated as catalysts for thiophene and pyrrole electropolymerization in acetonitrile and water. In a series of cyclic voltammetry experiments, catalysts were found to dramatically reduce the initial oxidation potential of the monomers. Hereby, the catalytic effect depended on the electrophilic nature of the catalyst centre, which is majorly influenced by the nature of the ligands. A Raman spectroscopy study demonstrated a decreased aromaticity of the monomers in contact with appropriate catalysts. By exemplarily investigating the catalysing effect of butyric acid on pyrrole polymerization in acetonitrile, conductive films with a lower charge transfer resistance resulted, as well as greater homogeneity and smoothness. Films were characterized by electrochemical impedance spectroscopy, white light interferometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, as well as surface-enhanced Raman spectroscopy. The catalysts presented in this communication convince with low prices and high solubility in acetonitrile and water, are already available in most labs, and can therefore serve as universal tools for the mild electropolymerization of well-known as well as novel monomers for innovative applications.

Activated Single-Phase Ti4 O7 Nanosheets with Efficient Use of Precious Metal for Inspired Oxygen Reduction Reaction.

The oxygen reduction reaction (ORR) is central to modern energy storage and conversion technologies for grids such as fuel cells and electrolyzers, but challenges remain due to the lack of reliable, economic, and durable electrocatalysts. Here, we develop single-crystal conductive black titanium (Ti4 O7 ) nanosheets (NSs) as a new precious metal carrier based on sacrificial hard templates and ultrasonic-assisted peeling, and deposit Pt clusters on Ti4 O7 NSs induced by wetness impregnation under the irradiation of visible light (VI; 650 nm). Pt/Ti4 O7 NSs provide Ti3+ , Pt2+ , and Pt0+ continuous active sites for the ORR multielectron process, achieving synergy among them. The assistance of visible light not only makes a more uniform and smaller distribution of Pt nanoclusters, but also strengthens the charge transfer, thereby constructing a strong metal-support interaction interface. VI-Pt/Ti4 O7 NSs show superior initial oxidation potential and a mass activity of 1.61 A mg-1 Pt at a E1/2 =0.91 V, which is nine times higher than that of commercial Pt/C. This work provides an effective strategy for achieving high-value applications of titanium sub-oxides and further explores the enhanced interface in metals Tin O2n-1 by light radiation.

Catalysing electropolymerization: High-quality polythiophene films for electrochemical sensors by the utilization of fluorine based Lewis acid catalysts

Polythiophene and other conductive polymers can be obtained by electropolymerization from various solvents, of which boron trifluoride diethyl etherate (BFEE) is preferably used. In this solvent, electropolymerization can be performed at significantly lower potentials and therefore milder conditions, from which polymers with improved properties result. However, their quality cannot easily be reproduced. We discovered the mechanism behind the decreased initial oxidation potential of thiophene in BFEE and transferred it onto stable solvents by the utilization of fluorine based Lewis acid catalysts. By exemplarily utilizing zinc fluoride in acetonitrile, we found that the catalysis allows for lower oxidation potentials, higher selectivity of polymerization, and smoother film surface morphology – in a reproducible manner. The presented polythiophene films constitute a promising substrate material for the fabrication of electrochemical sensors. Films were deposited by cyclic voltammetry, chronoamperometry, and chronopotentiometry, and characterized by electrochemical impedance spectroscopy and Raman spectroscopy. Surface morphology and elemental composition were analysed with white light interferometry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. We propose a number of alternative catalysts that can be utilized in various solvents, not just for thiophene electropolymerization, but for various other conductive polymers. The presented catalysis can therefore serve as a universal tool for the synthesis of high quality conductive polymer films for innovative and trendsetting applications.

Bidirectional controlling synthesis of branched PdCu nanoalloys for efficient and robust formic acid oxidation electrocatalysis

Through a two-way control of hexadecyl trimethyl ammonium bromide (CTAB) and hydrochloric acid (HCl), the PdCu nanoalloys with branched structures are synthesized in one step by hydrothermal reduction and used as electrocatalysts for formic acid oxidation reaction (FAOR). In this two-way control strategy, the CTAB is used as a structure-oriented surfactant, while a certain amount of HCl is used to control the reaction kinetics for achieving gradual growth of multi-dendritic structures. The characterizations including scanning transmission electron microscope (STEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) suggest that PdCu nanoalloys with unique multi-dendritic branches have favorable electronic structure and lattice strain for electrocatalyzing the oxidation of formic acid. In specific, among the electrocatalysts with different Pd/Cu ratios, the Pd1Cu1 branched nanoalloys have the largest electrochemically active surface area (ECSA) and the best performance for the FAOR. The catalytic activity of the Pd1Cu1 branched nanoalloys is 2.4 times that of commercial Pd black. After the chronoamperometry test, the Pd1Cu1 branched nanoalloys still maintain their original morphologies and higher current density than that of the commercial Pd black. In addition, in the CO-stripping tests, the initial oxidation potential and the oxidation peak potential of the PdCu branched nanoalloys for CO adsorption are lower than those of commercial Pd balck, evincing their better anti-poisoning performance.

Effect of pH Value on Electroless Deposition of Copper Graphite Powders

The effect of pH value on the electroless deposition of copper coated graphite powders (Cu@GPs) was investigated in this paper. The cathodic and anodic polarization curves were determined by linear sweep voltammetry in the plating at various pH value. pH value increasing can reduce the initial oxidation potential of formaldehyde, increase peak current density and accelerate electroless copper nuclei generated by the reduction reaction. With increasing pH value Cu+ disproportionation reaction was inhibited. Through the complexation competition and discharge competition among them, Na2EDTA, –OH and TART affect the reduction of cupric ions. The increasing pH value promote the formation of copper nuclei on the surface of graphite powders. Uniform Cu@GPs were fabricated by optimizing the pH 12.5~13. The copper plating layer is tightly combined with graphite, and the coating is complete.

Synthesis and characterization of donor–acceptor type quinoxaline-based polymers and the corresponding electrochromic devices with satisfactory open circuit memory

Three novel conjugated polymers were successfully designed and synthesized via the Suzuki coupling reaction based on the donor–acceptor (D–A) strategy. In the synthetic process, a electron rich unit 6,8-dibromo-3,3-bis((octyloxy)methyl)-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine (ProDOT) was selected as the donor unit, 5,8-bis-(5-bromothiopen-3-yl)-2,3-bis-(4-decyloxy- phenyl)-quinoxaline (QX) as the acceptor unit, and benzene (B) was the bridging unit. The three polymers are named PBQT-1, PBQT-2 and PBQT-3 by different feed ratios (B:QX:ProDOT) of 2:1:1, 3:2:1 and 3:1:2, respectively. Next, the polymers films are characterized in detail by a variety of instrumental methods. And, the electrochromic devices (ECDs) is also built by employing PBQT-1 and Poly (3,4-ethylenedioxythiophene)(PEDOT) as the anodically coloring material and cathodically coloring material, respectively, which also exhibits the satisfactory open circuit memory. All three polymers display the abundant and obvious color changes, including orange-khaki-dimgray (PBQT-1), brown-tawny-light army green (PBQT-2) and tangerine-brown yellow-light gray (PBQT-3). Meanwhile, the three polymers exhibit medium band gaps and excellent thermal stability, and the initial oxidation potential and optical band gap of the polymers are decreased gradually with the increasing of donor unit. It indicates that the different donor–acceptor ratios can effectively modify the band gap values and colors of the polymers, and provide the prospect to obtain the desired properties. The above results demonstrate that three polymers are anticipated to be the promising candidate for the neutral orange-color electrochromic (EC) materials, deserving more attentions and researches.

Synthesis, electrochromic properties and flash memory behaviors of novel D-A-D polyazomethines containing EDOT and thiophene units

A series of novel polyazomethines containing EDOT and thiophene units coded as PEDOTs (PEDOT-TPA, PEDOT-TDD, PEDOT-THIO, PEDOT-APM) and PTHIOs (PTHIO-TPA, PTHIO-TDD, PTHIO-THIO, PTHIO-APM) were synthesized successfully. They were gained in short time, low cost and mild reaction conditions by a straightforward synthetic path. It can be easily found from the electrochemical properties of these polymers that the polymers containing 3,4-ethylenedioxythiophene (EDOT) unit (PEDOTs) have lower initial oxidation potentials as compared to the polymers containing thiophene unit (PTHIOs). Spectroelectrochemical properties reveal that all of the polymer films exhibit outstanding multielectrochromic behaviors, distinct color contrast and excellent electrochemical stabilities. Kinetic studies show that the PEDOT-TPA film has the shortest response time (a color switching time of 4.54 s and a bleaching time of 3.88 s at 428 nm) and the PEDOT-THIO film exhibits the highest CE of 343.56 cm 2 C −1 . Typical I-V characteristics of the ITO/plymer/Al memory devices exhibit that all the memory devices based on PEDOTs and PTHIOs exhibited nonvolatile flash memory characteristics, with an ON/OFF current density ratio of 10 3 -10 4 and low threshold voltages (around 1 V). Thus, these characteristics illustrate that these novel polymers have great potential in optoelectronics applications as electrochromic materials and memory devices. • Eight kinds of novel polyazomethines were synthesized successfully by a straightforward synthetic path. • All of these polyazomethines exhibit outstanding electrochromic behavior and excellent electrochemical stability. • The polymers containing 3,4-ethylenedioxythiophene (EDOT) units (PEDOTs) have low initial oxidation potential. • Among these polymers, the PEDOT-TPA film has the shortest response time and the PEDOT-THIO film exhibits the highest CE. • All the memory devices exhibited nonvolatile flash memory characteristics.

Crystalline nickel boride nanoparticle agglomerates for enhanced electrocatalytic methanol oxidation

In this paper, crystalline Ni3B nanoparticle agglomerates have been successfully prepared via dry-powder annealing of the solution-produced amorphous nickel boride. The electron microscopy (EM) images indicate that the Ni3B nanomaterial is composed of numerous nano-sized particles with a diameter ranging from 100 to 200 nm. The electrocatalytic characteristics of nickel boride in an alkaline medium were observed by cyclic voltammetry (CV) and chronoamperomerty (CA). Compared to the amorphous nickel boride/Ni foam (ANB/NF), the crystalline Ni3B/Ni foam (CNB/NF) electrode exhibits a higher catalytic performance with low initial oxidation potential of 0.35 V and a high anodic oxidation current density of 62 A g−1 at 0.55 V in a 6 M KOH solution with 0.5 M methanol. And the CNB/NF electrode shows good long-term cycling stability and the catalytic current of methanol retains 87% of the initial value after 1000 time cycles. The CNB/NF electrode should be a promising candidate for alkaline direct methanol fuel cells (DMFCs).

Effect of graphene on the performance of nickel foam-based CoNi nanosheet anode catalyzed direct urea-hydrogen peroxide fuel cell

The highly porous electrode of a crisscrossed CoNi nanosheets array grown on reduced graphene oxide decorated Ni foam (CoNi/rGO@Ni foam) is fabricated through a facile dip and dry method followed by electroreduction and electrodeposition methods. The phase composition and morphology of the electrode are characterized by XRD, SEM, TEM, and EDS. In single electrode tests, CoNi/rGO@Ni foam electrode displays an excellent catalytic performance (330 mA cm−2 at 0.6 V) and stability towards urea electrooxidation when comparing to Ni foam and CoNi nanosheets modified Ni foam (CoNi@Ni foam) electrode. Besides, a low initial oxidation potential of urea electro-oxidation to 0.14 V is achieved on the CoNi/rGO@Ni foam electrode. The introducing of rGO to the electrode greatly reduced the reaction activation energy from 14.47 to 10.35 kJ mol−1. Besides, large active surface area (261.67 cm2) is also obtained from the electrode. The CoNi/rGO@Ni foam anode exhibits a maximum power density of 12.58 mW cm−2 in direct urea-hydrogen peroxide fuel cell tests. Excellent performance shows in single electrode tests and fuel cell tests suggest that addition of rGO to the electrode is an easy and feasible method to enhance the performance of the catalyst.

Nickel phosphate-based materials with excellent durability for urea electro-oxidation

Nickel phosphates (NiPO-a, NiPO-b, NiPO-c, NiPO-d) with different structures are developed by different methods. The mesostructure of NiPO-a is composed of less-ordered nanotubes of different lengths and NiPO-b, NiPO-c are arranged by a kind of flower-like nanosheet porous film. While, NiPO-d is composed of stacked nanocrystals. These nickel phosphates are examined by electrochemical tests to investigate the electrochemical activity of urea oxidation under alkaline conditions. Compared with commercial NiO, the four kinds of nickel phosphates have a more negative initial oxidation potential, which are more likely to react chemically with urea. As to NiPO-c, the highest oxidation current density for urea oxidation and superior stability are observed. During a 96-hour amperometric i-t test, the surface of NiPO-c modified fluorine-doped tin dioxide transparent conductive glass (FTO) electrode does not fall off, and the electrochemical activity just reduces 2.52% compared with the maximum value. NiPO-c has great potential for large-scale production in the field of urea-rich wastewater treatment and energy consumption.

Greatly Enhanced Intermolecular π-Dimer Formation of a Porphyrin Trimer Radical Trications through Multiple π Bonds

A trefoil-like porphyrin trimer linked by triphenylamine (TPA-TPZn(3)) was synthesized. A three-electron oxidation of TPA-TPZn(3) forms a radical trication (TPA-TPZn(3)(3+)), in which each porphyrin ring undergoes a one-electron oxidation. The radical trication TPA-TPZn(3)(3+) spontaneously dimerizes to afford (TPA-TPZn(3))(2)(6+) in CH(2)Cl(2) . The characteristic charge-resonance band due to the charge delocalization over the π system of (TPA-TPZn(3))(2)(6+) was observed in the NIR region. The initial oxidation potential of TPA-TPZn(3) is negatively shifted relative to that of the corresponding monomer porphyrin, which results from the stabilization of the oxidized state of TPA-TPZn(3) associated with the dimerization. The thermodynamic parameters (i.e., ΔH, ΔS, and ΔG) for the formation of (TPA-TPZn(3))(2)(6+) were determined by measuring Vis/NIR spectra at various temperatures. The formation constant of (TPA-TPZn(3))(2)(6+) is significantly larger than that of the radical cation dimer of the corresponding monomer porphyrin (e.g., over 2000-fold at 233 K). The electronic states were investigated using EPR spectroscopic analysis. The greatly enhanced dimerization of TPA-TPZn(3)(3+) results from multiple π-bond formation between the porphyrin radical cations.

Characterization of air-formed surface oxide film on Ti–29Nb–13Ta–4.6Zr alloy surface using XPS and AES

The surface oxide film on a Ti–29Nb–13Ta–4.6Zr alloy (TNTZ) was precisely characterized using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) to understand the composition and chemical state of the surface oxide film of TNTZ. For comparison, the component metals, titanium, niobium, tantalum, and zirconium, were also characterized to consider the effect of those on the formation of the surface oxide film on their alloy. The characterization of the surface oxide films on TNTZ and its component revealed the following issues. The surface oxide film on TNTZ consists of a composite oxide that contains titanium, niobium, tantalum, and zirconium but forms continuous layer and is very thin, ca. 3.7 nm. The oxide film is not completely oxidized because it contains various valences of cations. In particular, the oxidation of tantalum is inhibited in the oxide. Tantalum is enriched in the substrate in TNTZ just under the surface oxide because of this inhibition in the oxidation. The formation of the surface oxide film in TNTZ is predominantly governed by titanium. The preferential oxidation of an element is not always dependent on the initial oxidation potential of that element, the relationship between the oxidation energy from a smaller valence to a larger valence, and the dehydration process. In other words, a complicated competition governs the resultant composition of surface oxide.

Combination of Different Electrochemical Techniques to Characterize the Anodic Behaviour of Chromium

A literature survey on the active dissolution and passive state of pure chromium in acidic solutions revealed that there is considerable discrepancy concerning the properties of the anodic passive film on Cr. The conclusions concerning especially the type of conductivity of the anodic film at different potentials were contradictory. This work was undertaken to clarify the anodic behaviour of Cr using a combination of several experimental techniques, including in situ dc resistance measurements with the contact electric resistance (CER) technique. Rotating ring disk electrode measurements in the active dissolution region showed that release of soluble Cr species proceeds in solutions with a pH of 5, in contradiction with earlier reports which had indicated that active dissolution occurs only at pH 0.7 V, i.e. at potentials approaching the transpassive region. Photocurrent measurements pointed to an almost opposite behaviour as a function of potential, and the change in the sign of the photocurrent was dependent on the initial oxidation potential. Measurements performed using the CER technique indicated that irreversible changes in the film properties take place at high potentials in the passive region. This lead us to suggest that different layers of the film determine the photoresponse and the capacitive behaviour of the electrode.

Polypyrroles prepared by chemical oxidative polymerization at different oxidation potentials

Chemical oxidative polymerization of pyrrole is carried out by use of ferric chloride at various values of the initial oxidation potential. We found that the electrical conductivity depends heavily on the oxidation potential. Furthermore, the electrical conductivity of polypyrrole prepared in a binary solution was astonishingly enhanced compared to that obtained in a pure solution. In fact, one can obtain up to 328 S cm −1 for the maximum conductivity of pyrrole by controlling the oxidation potential in a binary solution of acetonitrile and methanol. We also found that the peak intensity of X-ray diffraction patterns and the reversibility of the redox property of polypyrrole are closely related to the oxidation potential. We conclude that the quality of polypyrrole including the electrical conductivity can be extremely enhanced if the oxidation potential is controlled in a refined manner by use of binary solvent systems.