Electrochemical Oxidation Properties Research Articles

Voltammetric Detection of Ascorbic Acid at Organic Conducting Polymers Electrodes and Flow Injection Analysis

In this paper, a sensitive and rapid modified electrode for the determination of Ascorbic Acid (AA) is proposed. In this study, active compound AA was determined from commercial drug form based on electrochemical oxidation properties at various conducting polymer electrodes by voltammetric methods. Electrodes modified by the electrodeposition of conducting organic polymers such as poly(3-methylthiophene, PMT), polypyrrole (PPY) and polyaniline (PAN) were used as chemical sensors for voltammetric analysis and flow injection detection of AA. The electrochemical behavior of AA at conducting polymer electrodes was compared and the effects on behavior of electrolyte type and its pH and the film thickness were systematically examined. The results showed that the proposed modified surface catalyzes the oxidation of AA. Electrocatalytic efficiency decreases in order of PMT > PPY > PAN. Voltammetric peak positions were affected by the nature of the electrolyte and its pH. Also, the effect of increasing film thickness was to observe increased peak heights for oxidation potential of AA. The best results for the determination of AA were obtained by DPV in Na2SO4 (pH 2.0) and PMT electrodes. Polymer coated electrodes were also used in an amperometric detector for flow injection analysis of AA. The responses of the polymer electrode were 5–15 times larger as compared to those of bare platinum. PMT showed improved performance as an amperometric detector for flow injection analysis systems over other types of polymer electrodes. Detection limits as low as 1×10−9 M were achieved using the PMT, compared to 1×10−6 M using platinum electrodes.

Influence of Acid on Ring-Opening, Fluorescence, Aggregation, Electrochemical Oxidation, and C–C Bond Coupling of Spiropyran Derivatives

Two benzothiazolinic spiropyran derivatives differently substituted at phenolic segment were synthesized to study the effect of acid on their ring-opening and electrochemical oxidation properties. Upon protonation, conventional spiropyrans undergo Cspiro–O bond breakage, resulting in the formation of their ring-open protonated cisoid merocyanine form, which rearranges itself to its stable transoid merocyanine. Benzothiazolinic spiropyrans have also displayed pH-controlled photochromism, with the spiro moiety being opened by trifluoroacetic acid and reverted to spiro form on neutralization with triethylamine. It was demonstrated that the increase in the concentration of trifluoroacetic acid (TFA) influences the rate of ring-opening permitting its identification by 1H NMR, 2D NMR, UV Visible spectroscopy, and single-crystal X-ray crystallography. The aggregation-induced emission characteristics of benzothiazolinic spiropyrans were also explored using fluorescence and DLS measurements. Moreover, the thia-indoline segment of spiropyran undergoes electrochemical oxidation followed by C–C coupling due to the presence of electron-rich nitrogen and sulfur atoms. The influence of acid on electrochemical oxidation and substituent was also investigated. Further, the density functional theory (DFT) based studies were performed to study the electrochemical oxidation and acidochromism in benzothiazolinic spiropyrans. Time-dependent DFT estimated variables also provided additional information regarding the acidochromism process.

Potentiometric C2H4-Selective Detection on Solid-State Sensors Activated with Bifunctional Catalytic Nanoparticles

This work presents a solid-state ionic-based device to selectively detect C2H4 in car exhaust gases. The sensor consists of 8YSZ as the electrolyte and two electrodes: Fe0.7Cr1.3O3/8YSZ and LSM/8YSZ. The main aim of this work is to optimize the catalytic behavior of the working electrode to C2H4 and reduce cross-sensitivity toward CO and H2O. Several catalyst nanoparticles were infiltrated to tailor C2H4 adsorption and electrochemical oxidation properties while diminishing adsorption and conversion of other gas components such as CO. The infiltrated metal catalysts were selected, taking into account both adsorption and redox properties. Infiltration of Ti or Al, followed by a second infiltration of Ni, enabled the selective detection of C2H4 with low cross-sensitivity toward CO and H2O in a moist gas environment. Further insight into potentiometric C2H4 sensing is achieved by electrochemical impedance analysis of the electrodes activated with bifunctional catalysts.

(Invited) Current Status and Bottlenecks of the Intercalation of Mg into Spinel Oxides

Electrochemical energy storage was an important enabler of the wireless revolution and it is touted as a key component of a society that shifts away from its dependence on fossil fuels. Li-ion batteries are the primary technology when high energy devices are required. However, despite their improved functionality over older systems (e.g. lead-acid car batteries), they do not quite yet meet the emerging energy demands in transportation and grid markets. This roadblock sparked interest in the development of batteries that utilize Mg2+ as ionic carrier. Theoretical predictions indicate that couples exist between a Mg metal negative electrode and oxide positive electrodes that could surpass the current practical limits of current devices. However, severe practical challenges have limited the study of the electrochemical properties of oxides to the simple elucidation of the viability and reversibility of the fundamental reactions of intercalation of Mg2+. Among the candidate oxides, the general family of spinel-type M2O4 (M=transition metal) are considered as leading contenders [1, 2]. In this talk, we will present the most up-to-date insight into the ability of spinel oxides to diffuse Mg2+. These observations will be paired with the outcomes of electrochemical reactions in non-aqueous electrolytes, since the use of Mg metal requires rigorously anhydrous environments. We will discuss the evidence supporting intercalation of Mg2+, and describe changes that correlate with both the identity of M and the existence of defects in the spinel structure [2, 3]. Critical to the endeavor is the ability to synthesize particles at small dimensions, as is the characterization of chemical and physical phenomena using a combination of tools providing information at different scales. The discussion will naturally lead us to reveal foundational bottlenecks that must be overcome to make Mg electrochemistry viable for energy storage. Liu et al., Energy Environ. Sci. 2015, 8, 964. Kim et al., Adv. Mater. 2015, 27, 3377. Hu et al., Nanoscale 2019, 11, 639.

(Invited) Current Status and Bottlenecks of the Intercalation of Mg into Spinel Oxides

Electrochemical energy storage was an important enabler of the wireless revolution and it is touted as a key component of a society that shifts away from its dependence on fossil fuels. Li-ion batteries are the primary technology when high energy devices are required. However, despite their improved functionality over older systems (e.g. lead-acid car batteries), they do not quite yet meet the emerging energy demands in transportation and grid markets. This roadblock sparked interest in the development of batteries that utilize Mg2+ as ionic carrier. Theoretical predictions indicate that couples exist between a Mg metal negative electrode and oxide positive electrodes that could surpass the current practical limits of current devices. However, severe practical challenges have limited the study of the electrochemical properties of oxides to the simple elucidation of the viability and reversibility of the fundamental reactions of intercalation of Mg2+. Among the candidate oxides, the general family of spinel-type M2O4 (M=transition metal) are considered as leading contenders [1, 2]. In this talk, we will present the most up-to-date insight into the ability of spinel oxides to diffuse Mg2+. These observations will be paired with the outcomes of electrochemical reactions in non-aqueous electrolytes, since the use of Mg metal requires rigorously anhydrous environments. We will discuss the evidence supporting intercalation of Mg2+, and describe changes that correlate with both the identity of M and the existence of defects in the spinel structure [2, 3]. Critical to the endeavor is the ability to synthesize particles at small dimensions, as is the characterization of chemical and physical phenomena using a combination of tools providing information at different scales. The discussion will naturally lead us to reveal foundational bottlenecks that must be overcome to make Mg electrochemistry viable for energy storage. 1. Liu et al., Energy Environ. Sci. 2015, 8, 964.2. Kim et al., Adv. Mater. 2015, 27, 3377. 3. Hu et al., Nanoscale 2019, 11, 639.

Investigation of the Electrochemical Behavior of Hydroquinone at Some Conducting Polymer Electrodes and Amperometric Detection

In this paper, a rapid and sensitive modified electrode for the determination of hydroquinone (HQ) is proposed. In this study, active compound HQ was determined from commercial drug form based on electrochemical oxidation properties at various electrodes by voltammetric methods. Electrodes modified by the electrodeposition of conducting organic polymers such as poly(3-methylthiophene, PMT), polypyrrole (PPY) and polyaniline (PAN) were used as chemical sensors for voltammetric analysis and flow injection detection of HQ. The electrochemical behavior of HQ at conducting polymer electrodes was compared and the effects on behavior of electrolyte type and its pH and the film thickness were systematically examined. The results showed that the proposed modified surface catalyzes the oxidation of HQ. Electrocatalytic efficiency decreases in order of PMT > PPY > PAN. Voltammetric peak positions were affected by the nature of the electrolyte and its pH. Also, the effect of increasing film thickness was to observe increased peak heights for oxidation potential of HQ. The best results for the determination of HQ were obtained by DPV in Na2SO4 (pH 2.0) and PMT electrodes. Polymer coated electrodes were also used in an amperometric detector for flow injection analysis of HQ. The responses of the polymer electrode were 5–15 times larger as compared to those of bare platinum. PMT showed improved performance as an amperometric detector for flow injection analysis systems over other types of polymer electrodes. Detection limits as low as 1 × 10–9 M were achieved using the PMT, compared to 1 × 10–6 M using platinum electrodes.

Electrochemical Detection of Epinephrine at Organic Conducting Polymers Electrodes

In this paper, a rapid and sensitive modified electrode for the determination of Epinephrine (EP) is proposed. In this study, active compound EP was determined from commercial drug form based on electrochemical oxidation properties at various electrodes by voltammetric methods. Electrodes modified by the electrodeposition of conducting organic polymers such as poly(3-methylthiophene, PMT), polypyrrole (PPY) and polyaniline (PAN) were used as chemical sensors for voltammetric analysis and flow injection detection of EP. The electrochemical behavior of EP at conducting polymer electrodes was compared and the effects on behavior of electrolyte type and its pH and the film thickness were systematically examined. The results showed that the proposed modified surface catalyzes the oxidation of EP. Electrocatalytic efficiency decreases in order of PMT > PPY > PAN. Voltammetric peak positions were affected by the nature of the electrolyte and its pH. Also, the effect of increasing film thickness was to observe increased peak heights for oxidation potential of EP. The best results for the determination of EP were obtained by DPV in Na2SO4 (pH 2.0) and PMT electrodes. Polymer coated electrodes were also used in an amperometric detector for flow injection analysis of EP. The responses of the polymer electrode were 5–15 times larger as compared to those of bare platinum. PMT showed improved performance as an amperometric detector for flow injection analysis systems over other types of polymer electrodes. Detection limits as low as 1× 10–9 M were achieved using the PMT, compared to 1 × 10–6 M using platinum electrodes.

Investigation of the Electrochemical Behavior of p-Aminophenol at Various Conducting Polymers Electrodes

In this study, p-aminophenol (p-AP) was determined from commercial drug form based on electrochemical oxidation properties at various electrodes by voltammetric methods. Electrodes modified by the electrodeposition of conducting polymers such as poly(3-methylthiophene, PMT), polypyrrole (PPY) and polyaniline (PAN) were used as chemical sensors for voltammetric analysis and flow injection detection of p-AP. The electrochemical behavior of p-AP at conducting polymer electrodes was compared and the effects on behavior of electrolyte type and its pH and the film thickness were systematically examined. The results showed that the proposed modified surface catalyzes the oxidation of p-AP. Electrocatalytic efficiency decreases in order of PMT > PPY > PAN. Voltammetric peak positions were affected by the nature of the electrolyte and its pH. Also, the effect of increasing film thickness was to observe increased peak heights for oxidation potential of p-AP. The best results for the determination of p -AP were obtained by DPV in Na2SO4 (pH 2.0) and PMT electrodes. Polymer coated electrodes were also used in an amperometric detector for flow injection analysis of this compound. The responses of the polymer electrode were 5–15 times larger as compared to those of bare platinum. PMT showed improved performance as an amperometric detector for flow injection analysis systems over other types of polymer electrodes. Detection limits as low as 1 nM were achieved using the PMT, compared to 1 μM using platinum electrodes.

Redox Property of Enamines.

Enamines are electron-rich compounds bearing intriguing redox properties. Herein, a series of secondary enamines condensed from primary amine and β-ketocarbonyls were synthesized and their electrochemical oxidation properties were systematically studied by cyclic voltammetry. Furthermore, theoretical calculation of oxidation potentials of enamines, particularly those catalytic intermediates, was also conducted to further broaden the scope investigated. Possible structural factors on oxidation and the nature of the resulted radical cation intermediates were revealed and discussed. Correlation of redox potentials with molecular properties such as highest occupied molecular orbital energies and natural population analysis charge were explored, and there appears no simple linear correlation. On the other hand, a good correlation with Mayr's nucleophilicity parameter N was noted among a range of catalytically relevant enamines. Spin population analysis disclosed that enamine radical cations mainly exhibit the carbon-center free radical feature. Taking experimental and computation data together, a comprehensive picture about the redox property of enamines is presented, which would provide guidance in the development of oxidative enamine catalysis and transformations.

Electrochemical oxidation of rhodamine B by PbO2/Sb-SnO2/TiO2 nanotube arrays electrode

A PbO2/Sb-SnO2/TiO2 nanotube array composite electrode was successfully synthesized and its electrochemical oxidation properties were investigated. Field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) results showed that the PbO2 coating was composed of an α-PbO2 inner layer and a β-PbO2 outer layer. Accelerated life measurement indicated that the composite electrode had a lifetime of 815 h. Rhodamine B (RhB) was employed as a model pollutant to analyze the electrocatalytic activity of the electrode. The effects of initial RhB concentration, current density, initial pH, temperature, and chloride ion concentration on the electrochemical oxidation were investigated in detail. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) results suggested that the concentration of leached Pb2+ in the electrolyte during the electrocatalytic oxidation process can be neglected. Finally, the degradation mechanism during the electrocatalytic oxidation process was proposed based on the results of solid-phase micro-extraction-gas chromatography-mass spectrometry (SPME-GC-MS). The high electrocatalytic performance of the composite electrode makes it a promising anode for the treatment of organic pollutants in aqueous solution.

Li4/3Ni1/3Mo1/3O2 – LiNi1/2Mn1/2O2 Binary System as High Capacity Positive Electrode Materials for Rechargeable Lithium Batteries

A binary system of x Li4/3Ni1/3Mo1/3O2 – (1–x) LiNi1/2Mn1/2O2 is studied as high-capacity positive electrode materials for rechargeable lithium batteries. Structural and electrochemical properties of oxides with different compositions in this binary system are examined. Mo ordering is retained for 1 ≤ x ≤ 1/3 with a monoclinic symmetry and disappears for x ≤ 1/6 with a rhombohedral symmetry. Compared with Li4/3Ni1/3Mo1/3O2, partial substitution of Mn for Mo lead to the improvement of reversible capacity and reduction of polarization. For Li6/5Ni2/5Mn1/5Mo1/5O2 (x = 1/3) and Li9/8Ni7/16Mn5/16Mo1/8O2 (x = 1/6), high reversible capacities of around 200 mAh g−1 are obtained. Improved cycling performance is achieved through the optimization of voltage ranges. Further structural characterization by ex–situ XRD reveals that the improved reversibility for the Mn-substituted samples mainly results from the suppression of Mo migration during cycling, probably associated with partial oxygen loss.

Connection Between Atomic Scale Characterization and Electrochemical Behavior during Passivation of Single Crystals on Ni-Cr and Ni-Cr-Mo Alloys

Ni-Cr and Ni-Cr-Mo alloys owe their outstanding corrosion resistance to the surface enrichment of passivating Cr(III) oxides and synergistic effect of Cr and Mo in case of Mo-containing alloys [1-3]. However, the specific roles of minor elements are not well understood especially with respect to precise location of Mo relative to the oxide/metal interface, nor the atomistic processes responsible for protective-oxide layer growth and breakdown. The composition, structure and thickness of the passivating oxide films are challenging to characterize considering their nanoscale dimensions and the high electric field imposed during growth in solution. Key processes that take place within the oxide and regulate passivation are controlled by defect interactions that are atomic, ionic, and electronic in nature and currently poorly understood, often needed to be studied at the resolution and detection limits of experimental methods [4]. Common electrochemical methods such as AC and DC electrochemistry are rarely connected with atomic scale ex situ techniques such as scanning tunneling (STM), atomic force (AFM) and transmission electron (TEM) microscopies to yield crucial information on structure, molecular and electronic properties of the oxides [5]. The main goal of this work is to integrate single crystal electrochemical measurements with nanoscale characterization to advance fundamental understanding and eventually predict the roles of Cr and Mo on surface stability in corrosive environments. Such a connection between global electrochemistry and atomic studies is infrequently reported [6].Polycrystalline alloys contain many grain orientations that may affect passivation behavior [7]. This work focuses on examining the oxide growth kinetics on single crystals. It is expected that grain surface facet evolution and oxide thickness will vary according to crystallographic orientation [8, 9]. Model alloys Ni-22Cr and Ni-22Cr-6Mo, wt%, were arc-melted, cold-rolled to achieve ~12% deformation, and then heat treated to allow for re-crystallization and growth of sufficiently large grains to enable electrochemical measurements. A ~4 mm2 area of a sample was first scanned with Electron Backscattered Diffraction (EBSD) to obtain a “catalog” of grain orientations, and then each grain within the EBSD map was probed regarding its electrochemical behavior. The kinetics of the passive state of single grains were determined potentiostatically at +0.2 VSCE in solution, where a previously formed on air oxide was partially reduced at -1.3 VSCE. Electrochemical impedance spectroscopy (EIS) was then collected after various stages of oxide growth and the data was fit assuming a constant phase element to enable calculation of thickness [10]. Oxide charge formation, current density, and thickness for each alloy and grain orientation were studied using Mott-Cabrera and Point Defect models. Ex situ Raman and XPS conducted on polycrystalline samples aided in determining molecular identity and the efficiency of oxide growth versus dissolution. AFM topography images and profiles across single grain surfaces at intermediate stages of potentiostatically controlled oxide growth were obtained to give insight on the nucleation and morphology of oxides formed on various grains (Figure 1a). Furthermore, the structural and electrochemical properties of oxides grown potentiostatically on specific crystallographic orientations were correlated with the TEM analysis performed on the oxides grown chemically under equivalent conditions using potassium persulfate or hydrogen peroxide oxidants. It was found the EIS, TEM and XPS oxide thicknesses were in agreement with each other. The broader relevancy of this presentation, besides connecting electrochemistry and nano- to mesoscale characterization, is its contribution to concepts beneficial towards development of predictive correlations associated with the passivity of Ni alloys during aqueous exposure. Acknowledgements This project was funded by U.S. ONR (SP0028970-PROJ0007990) and MURI Program under the direction of Dr David Shifler (N00014-14-1-0675).

Synthesis of New Types of Ferrocene Dimers Bridged by a Fused Oligothiophene Spacer and Study of Their Electrochemical Oxidation Process via a Mixed‐Valence State

ABSTRACTWe describe the synthesis and electrochemical oxidation properties of ferrocene dimers bridged by a fused oligothiophene spacer (thienothiophene, benzodithiophene, and dithienothiophene), which are designed as new types of ferrocene dimers for the study of the oxidation process via a mixed‐valence state. The electrochemical properties of all ferrocene dimers were examined by a cyclic voltammetry technique. The voltammograms showed a reversible two‐electron oxidation wave derived from the two ferrocene fragments with a potential difference between the first and second oxidation waves (ΔE1/2 = E1/2(+1/+2) – E1/2(0/+1)), which ranges from 0 to +127 mV. This result indicates that the chemical structure of the fused oligothiophene spacer can be attuned to the two‐electron oxidation process of two ferrocene terminals via a mixed‐valence state.

Effect of pH on the Electrochemical Properties of Oxides formed over β – Ti-15Mo and Mixed Ti-6Al-4V Alloys

Effect of pH on the Electrochemical Properties of Oxides formed over β – Ti-15Mo and Mixed Ti-6Al-4V Alloys

Electrochemical Degradation Characteristics of Refractory Organic Pollutants in Coking Wastewater on Multiwall Carbon Nanotube‐Modified Electrode

The multiwall carbon nanotube‐mollified electrode (MWCNT‐ME) was fabricated and its electrocatalytic activity of refractory organic pollutants of coking wastewater was investigated. The surface morphology, absorption properties, and the electrochemical behavior of phenol and aniline at the MWCNT‐ME were analyzed. Using ultraviolet‐visible adsorption spectroscopy (UV‐vis), Gas chromatography mass spectrometry (GC/MS), and chemical oxygen demand (COD) test, the electrochemical oxidation properties of refractory organic pollutants of coking wastewater using the MWCNT‐ME and the IrSnSb/Ti electrode were analyzed. Compared with the powder adsorption media, the MWCNT‐ME was proved to have weaker adsorption activity, which means electrochemical degradation is the decisive factor of the removal of organic pollutants. The MWCNT‐ME shows high electrochemical reactivity with oxidation peaks of 0.18 A and 0.12 A for phenol and aniline, respectively. Under the same working conditions, the MWCNT‐ME COD removal rate 51% is higher than IrSnSb/Ti electrode’s rate 35%. The MWCNT‐ME has application potential of electrochemical oxidation of refractory organic pollutants of coking wastewater.

Synthesis and [2+2] Cycloaddition with Tetracyanoethylene of Ene–Diyne Scaffolds Bearing Ferrocenes at the Periphery

AbstractThe ene–diyne systems 1 and 2, possessing ferrocenyl groups at the periphery, were prepared by a simple one‐pot Sonogashira–Hagihara coupling reaction of ethynylferrocene with 9‐dibromomethylene‐9H‐fluorene (4) and 9,10‐bis(dibromomethylene)‐9,10‐dihydroanthracene (5). Ene–diyne 1 reacted with tetracyanoethylene (TCNE) in a formal [2+2] cycloaddition reaction, followed by ring opening of the initially formed [2+2] cycloadduct, cyclobutene, to afford the corresponding 1,1,4,4‐tetracyanobutadiene (TCBD) derivative 6 in good yield. The redox behavior of the ene–diyne compounds 1 and 2, and the TCBD derivative 6 was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their electrochemical oxidation properties with multi‐electron transfer depending on the number of ferrocene units in the molecule, in addition to the two‐electron reduction of the TCBD moiety in the case of TCBD derivative 6. Moreover, a significant color change was observed by visible spectroscopy under electrochemical oxidation conditions and under reduction conditions in the case of TCBD derivative 6.

Electrochemical oxidation behavior of titanium nitride based electrocatalysts under PEM fuel cell conditions

Titanium nitride (TiN) is attracting attention as a promising material for low temperature proton exchange membrane fuel cells. With its high electrical conductivity and resistance to oxidation, TiN has a potential to act as a durable electrocatalyst material. Using electrochemical and spectroscopic techniques, the electrochemical oxidation properties of TiN nanoparticles (NP) are studied under PEM fuel cell conditions and compared with conventional carbon black supports. It is observed that TiN NP has a significantly lower rate of electrochemical oxidation than carbon black due to its inert nature and the presence of a native oxide/oxynitride layer on its surface. Depending on the temperature and the acidic media used in the electrochemical conditions, the open circuit potential (OCP) curves shows the overlayer dissolved in the acidic solution leading to the passivation of the exposed nitride surface. It is shown that TiN NP displays passive behavior under the tested conditions. The XPS characterization further supports the dissolution argument and shows that the surface becomes passivated with the O–H groups reducing the electrical conductivity of TiN NP. The long-term stability of the Pt/TiN electrocatalysts is tested under PEM fuel cell conditions and the trends of the measured electrochemical surface area at different temperatures is shown to agree with the proposed passivation model.

Electrochemical Oxidation Properties of Tetrakis(tert-butyl)phthalocyaninatozinc(II) in Non-Aqueous Media: A Reinvestigation into the Effects of Stacking, Axial Coordination, and Solvent

Abstract The electrochemical oxidation properties of tetrakis(tert-butyl)phthalocyaninatozinc, Zn(t-Bu4Pc), has been reinvestigated for the first systematic exploration in comparison with the authentic properties of porphyrin. The experimental conditions for the oxidation properties of the monomeric Zn(t-Bu4Pc) species were optimized in CH2Cl2 as a non-coordinating solvent to exclude the effect of axial coordination, although most of the previous studies employed coordinating solvents to overcome poor solubility. Employing dilute conditions with 0.1 M tetra-n-butylammonium hexafluorophosphate (n-Bu4N·PF6) as a supporting electrolyte, the effect of axial ligand and solvent on the oxidation behaviors of Zn(t-Bu4Pc) were newly analyzed. The effects of axial coordination on the oxidation properties of Zn(t-Bu4Pc) are discussed from the views of the kinetic process in the charge-compensating step, the structural deformation by axial coordination, and the σ-donation from the axial ligand to the d-orbital of the central zinc. Coordination of axial ligand and polar solvent results in an unusual positive shift of the oxidation potential of Zn(t-Bu4Pc). We propose a ligand dissociation mechanism for the oxidation processes of Zn(t-Bu4Pc) as a rational explanation for the experimental observations. The relevance of the electrochemical properties is supported by spectroscopic characterization.

Disruption of extended defects in solid oxide fuel cell anodes for methane oxidation

Point defects largely govern the electrochemical properties of oxides: at low defect concentrations, conductivity increases with concentration; however, at higher concentrations, defect-defect interactions start to dominate. Thus, in searching for electrochemically active materials for fuel cell anodes, high defect concentration is generally avoided. Here we describe an oxide anode formed from lanthanum-substituted strontium titanate (La-SrTiO3) in which we control the oxygen stoichiometry in order to break down the extended defect intergrowth regions and create phases with considerable disordered oxygen defects. We substitute Ti in these phases with Ga and Mn to induce redox activity and allow more flexible coordination. The material demonstrates impressive fuel cell performance using wet hydrogen at 950 degrees C. It is also important for fuel cell technology to achieve efficient electrode operation with different hydrocarbon fuels, although such fuels are more demanding than pure hydrogen. The best anode materials to date--Ni-YSZ (yttria-stabilized zirconia) cermets--suffer some disadvantages related to low tolerance to sulphur, carbon build-up when using hydrocarbon fuels (though device modifications and lower temperature operation can avoid this) and volume instability on redox cycling. Our anode material is very active for methane oxidation at high temperatures, with open circuit voltages in excess of 1.2 V. The materials design concept that we use here could lead to devices that enable more-efficient energy extraction from fossil fuels and carbon-neutral fuels.

Electrochemical properties of protective coatings on maraging steel

Electrochemical properties of oxides formed on 250 maraging steel in steam at elevated temperatures were compared to standard phosphating treatment. Polarization curves and time-to-pitting experiments established the advantage of these oxides over phosphating. Whereas the elongation of the oxide was low, and diffusion coefficient of hydrogen was not dramatically smaller than for bare maraging steel, the threshold stress in stress corrosion cracking studies was significantly higher for oxidized steel. It is postulated that these benefits arise from the austenitic sub-layer.