Anodic Oxidation Of Hydrazine Research Articles

The mechanism of hydrazine electro-oxidation revealed by platinum microelectrodes: role of residual oxides

The electrochemistry of hydrazine at platinum has been re-evaluated by an investigation using microelectrodes. Platinum oxides remaining from preceding oxidative scans results in hydrazine oxidation occurring up to ca. 400 mV more cathodic than at an oxide-free Pt electrode. The observed voltammetry at oxidised or 'activated' platinum electrodes was found to be a function of the immersion time (time since 'activation') and pH. Differences between phosphate, sulphate and acetate-based electrolytes are noted. The anodic hydrazine oxidation features at 'activated' electrodes occurred as a prewave or a prepeak, depending upon the electrolyte and scan rate employed. Although hydrazine is known to react with bulk Pt oxide, the loss of activation with time was found to be independent of hydrazine concentration and was instead a function of pH and supporting electrolyte, therefore the 'activation' corresponds to residual rather than bulk platinum oxide. The condition of platinum was examined by X-ray photoelectron spectroscopy (XPS), which demonstrated an increase in oxygen coverage with cycling and the absence of any strongly adsorbed or poisoning species. The facile oxidation of hydrazine has implications with regards to hydrogen storage, generation and fuel cells. The different effects corresponding to insufficient buffering, which has relevance to the electroanalytical detection of hydrazine, was also investigated.

Study of Pt-free anode catalysts for anion exchange membrane fuel cells

Unsupported transition-metal nanoparticles such as Ni, Co, and Ni x Co y (Ni 0.75Co 0.25, Ni 0.50Co 0.50, Ni 0.25Co 0.75) were synthesized by the liquid reduction process for application to the anode catalyst of Precious Metal-free Liquid feed Fuel Cells (PM-fLFCs) using hydrazine hydrate (N 2H 4·H 2O) for a fuel. Their electrocatalytic activities were evaluated by rotating disk electrode (RDE), and the mass activity of Ni 0.50Co 0.50 exhibited higher activity than other catalysts for the anodic oxidation of hydrazine in alkaline solution. The morphology and structure of these catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoemission spectroscopy (XPS). It has been indicated that Ni 0.50Co 0.50 has a coexistence effect by inhabitation of Co oxidation and significantly improve the electrooxidation of hydrazine. The excellent fuel cell performance, 0.891 V of open circuit voltage and 432 mW/cm 2 of high maximum power, was exhibited using Ni 0.50Co 0.50 catalysts.

Electrocatalytic oxidation of hydrazine at a Co(II) complex multi-wall carbon nanotube modified carbon paste electrode

The catalytic oxidation of hydrazine was investigated by a cobalt(II) bis (benzoylacetone) ethylenediimino multi wall carbon nanotube-modified carbon paste electrode (Co(II)BBAEDI-MWCNT-MCPE) as a highly sensitive electrochemical sensor. The effect of variables such as pH and modifier percent on cyclic voltammograms peak current was optimized. The modified electrode showed very efficient electrocatalytic activity for anodic oxidation of hydrazine in 0.1M phosphate buffer solution (pH 7.0). Anodic peak potential of hydrazine oxidation at the surface of modified electrode shifts by about 500mV toward negative values compared with that on the bare electrode. The diffusion coefficient and electron transfer coefficient of hydrazine were obtained using electrochemical approaches. The Co(II)BBAEDI-MWCNT-MCPE showed good reproducibility (RSD<3.3%). The electrocatalytic current increased linearly with the hydrazine concentration in the range of 0.3–70.0μM and detection limit was 0.1μM. The effect of various interferences on the hydrazine peak current was studied. This method was applied to determine hydrazine in water samples.

Electrocatalytic Oxidation of Hydrazine at a Cobalt(II) Schiff-Base-Modified Carbon Paste Electrode

Electrocatalytic oxidation and detection of hydrazine under pH 6.0 conditions were studied with a carbon paste electrode modified with a Co(II) Schiff base complex [, acid (2-hydroxy-3-methoxy-benzylidene)-hydrazide]. Anodic oxidation of hydrazine at the -modified carbon paste electrode occurred at low overpotential ( vs ), and treatment of the voltammetric data showed that it was a purely diffusion-controlled reaction involving one electron in the rate-determining step. The catalytic oxidation peak current was linearly dependent on the hydrazine concentration over the wide range to . The heterogeneous rate constant for the oxidation of hydrazine at the surface of the modified electrode was determined by rotating disk electrode voltammetry using the Koutecky–Levich plot. A Tafel plot, derived from voltammograms, indicated a one-electron charge-transfer process to be the rate-limiting step, and the overall number of electrons involved in the catalytic oxidation of hydrazine was found to be 4. The mechanism for the interaction of hydrazine with the complex-modified carbon paste electrode is proposed to involve the redox process.

Anodic Oxidation and Amperometric Sensing of Hydrazine at a Glassy Carbon Electrode Modified with Cobalt (II) Phthalocyanine–cobalt (II) Tetraphenylporphyrin (CoPc- (CoTPP)4) Supramolecular Complex

This paper describes the electrocatalytic behaviour of a glassy carbon electrode (GCE)modified with cobalt(II)phthalocyanine (CoPc) complex peripherally tetrasubstituted withcobalt(II)tetraphenylporphyrin (CoTPP) complexes via ether linkages (i.e., CoPc-(CoTPP)4). Thefeatures of the immobilised pentamer were interrogated with cyclic voltammetry andelectrochemical impedance spectroscopy (EIS) using [Fe(CN)6]3-/4- as redox probe revealedenhanced electron transfer properties with kapp ≈ 18 x 10-6 cms-1 compared to that of the bareGCE (4.7 x 10-6 cms-1). The viability of this supramolecular complex as a redox mediator for theanodic oxidation and sensitive amperometric determination of hydrazine in alkaline conditions isdescribed. The electrocatalytic oxidation of hydrazine by GCE-CoPc-(CoTPP)4 was characterisedwith satisfactory catalytic current response with low non-Faradaic current (ca. 30 times lowerthan the bare GCE) and at much lower oxidation potential (ca. 300 mV lower than the bareGCE). A mechanism for the studied electrocatalytic reaction was proposed based on thespectrophotometric evidence that revealed the major involvement of the Co(III)/Co(II) redox coupleof the central CoPc species rather than the CoTPP component of the pentamer. Rate constant forthe anodic oxidation of hydrazine was estimated from chronoamperometry as ~ 3x103 M-1s-1. Theproposed amperometric sensor displayed excellent charateristics towards the determination ofhydrazine in 0.2 M NaOH ; such as low overpotentials ( 100 mV vs Ag|AgCl), very fastamperometric response time (1 s), linear concentration range of up to 230 μM, with micromolardetection limit, high sensitivity and stability.

Electrocatalytic oxidation of hydrazine with pyrogallol red as a mediator on glassy carbon electrode

The anodic oxidation of hydrazine has been studied on a glassy carbon electrode by electrocatalytic effect of pyrogallol red as a homogenous mediator, using cyclic voltammetry, linear sweep voltammetry and chronoamperometry as diagnostic techniques. Using cyclic voltammetry study showed that, the catalytic current of the system depends on the concentration of hydrazine. The magnitude of the peak current for pyrogallol red increased sharply in the presence of hydrazine, and proportional to hydrazine concentration. The diffusion coefficient of hydrazine was also estimated using chronoamperometry. The chronoamperometry studies also were used to determine the catalytic rate constant for catalytic reaction of pyrogallol red with hydrazine. The experimental results showed that the peak current varied in the presence of different metal cations, but these effects were omitted in the presence of EDTA, while almost all of anions had no effect on the peak current of hydrazine. The proposed method was used for analysis of hydrazine in real samples.

Electrocatalytic oxidation and detection of hydrazine at gold electrode modified with iron phthalocyanine complex linked to mercaptopyridine self-assembled monolayer

Electrocatalytic oxidation and detection of hydrazine in pH 7.0 conditions were studied by using gold electrode modified with self-assembled monolayer (SAM) films of iron phthalocyanine (FePc) complex axially ligated to a preformed 4-mercaptopyridine SAMs. The anodic oxidation of hydrazine in neutral pH conditions with FePc-linked-mercaptopyridine-SAM-modified gold electrode occurred at low overpotential (0.35 V versus Ag|AgCl) and the treatment of the voltammetric data showed that it was a pure diffusion-controlled reaction with the involvement of one electron in the rate-determining step. The mechanism for the interaction of hydrazine with the FePc-SAM is proposed to involve the Fe (III)Pc/Fe (II)Pc redox process. Using cyclic voltammetry (CV) and Osteryoung square wave voltammetry (OSWV), hydrazine was detected over a linear concentration range of 1.3 × 10 −5 to 9.2 × 10 −5 mol/L with low limits of detection (ca. 5 and 11 μM for OSWV and CV, respectively). At concentrations higher than 1.2 × 10 −4 mol/L the anodic peak potential shifted to 0.40 V (versus Ag|AgCl), and this was interpreted to be due to kinetic limitations resulting from the saturation of hydrazine and its oxidation products onto the redox-active monolayer film. This type of metallophthalocyanine-SAM-based electrode is a highly promising electrochemical sensor given its ease of fabrication, good catalytic activity, stability, sensitivity and simplicity.

Anodic oxidation of hydrazine at carbon nanotube powder microelectrode and its detection

Carbon nanotube powder microelectrodes (CNTPMEs) were used to study the anodic oxidation of hydrazine at Carbon nanotube (CNT)—the novel carbon material. It was found that the electrochemical behaviours were greatly improved at CNTs, indicating that the anodic oxidation could be catalyzed at CNTs. The kinetics parameters of this process were calculated, the heterogeneous electron transfer rate constant k was 0.0019 cm s −1, (1− α) n α was 0.22. The CNTPMEs were also found with high sensitivity for hydrazine detection, could be used as hydrazine sensors.

Affinity of poly(phenylcyanomethylenefluorene) and poly(dicyanomethylenefluorene) towards metallic cations. Uses of the new interfaces in electrocatalysis

Abstract Anodic oxidation of 2(9 H -fluoren-9-ylidene)malononitrile and 2(9 H -fluoren-9-ylidene)-2-phenylacetonitrile leads to polyfluorenylidene possessing an affinity towards some metallic cations leading to polymer-metal composites. The efficiency of these new interfaces is presented during the anodic oxidation of hydrazine, formaldehyde, methanol, glucose and sodium azide. For this last substrate, the detection limit with our new polymer-metal composite is lower than 5 × 10 −5 M.

Anodic oxidation of hydrazine on glassy carbon electrodes in acetonitrile

The anodic oxidation kinetics of hydrazine on glassy carbon electrodes in acetonitrile were examined by cyclic voltammetry, a rotating ring-disc electrode technique and chronoamperometry. The experimental results of the rotating ring-disc electrode prove that hydrazine is oxidized to HNNH, which cannot be oxidized further in acetonitrile. Hydrazine molecules are adsorbed on the electrode surface. One-third of the adsorbed hydrazine molecules are oxidized to HNNH and the other two thirds act as proton acceptors. A possible mechanism of hydrazine oxidation is proposed.

Discovery of some new stable electrocatalytic materials for the anodic oxidation of hydrazine

Discovery of some new stable electrocatalytic materials for the anodic oxidation of hydrazine

The anodic oxidation of hydrazine on glassy carbon electrode

AbstractThe anodic oxidation kinetics of hydrazine (N2H4) on glassy carbon (GC) electrode was examined by cyclic voltammetry, rotating disk and ring‐disc electrode techniques. The possible mechanisms of N2H4 oxidation in both aqueous and nonaqueous solutions are proposed.

Anodic oxidation of hydrazine on glassy carbon modified by macrocyclic transition metal complexes: Part 1. Cobalt protoporphyrin dimethyl ester modified electrode

The electrocatalytic oxidation of hydrazine (N 2H 4) on a glassy carbon electrode (GC) modified by monolayer and polymer films of cobalt protoporphyrin dimethyl ester (CoPP) has been studied. Both the monolayer and polymer films of CoPP are very active to the anodic oxidation of N 2H 4. The activity of CoPP for the anodic oxidation of N 2H 4 is dependent on the pH of the solution, and the thickness of polymerized CoPP film. The oxidation kinetics were examined by methods of cyclic voltammetry, rotating disc electrodes and steady-state polarization measurement.

Anodic oxidation of hydrazine and its methylderivatives on bare Pt and Pt electrode surfaces modified by underpotential metal adsorbates in acetonitrile

The electrooxidation of hydrazine and its methylderivatives (methylhydrazine and 1,1-dimethylhydrazine) on bare Pt and Pt electrode surfaces modified by underpotential metal adsorbates was studied in acetonitrile. On bare Pt, one-third of the molecules of the substances under examination undergo a two-electron oxidation to the corresponding diimides, while the remaining number of molecules act as the required proton acceptors in neutral acetonitrile. In alkaline solutions, hydrazine undergoes a quantitative four-electron oxidation process, while its methyl derivatives are oxidized quantitatively to the corresponding diimides in the same media. The pronounced inhibition effects on hydrazine oxidation caused by underpotential T1 and Pb adsorbates were interpreted in terms of a change in the chemical interaction of hydrazine molecules and the electrode surface modified by the underpotential metal adsorbates.

Electrochemical reactions on some cemented metal carbides

The electrochemical behaviour of cobalt-cemented tungsten carbides has been examined in aqueous alkaline solutions. These electrodes exhibit a good surface stability in the potential region ca. 0.0 – 0.7 V ( vs. RHE); the presence of a passivating surface oxide is indicated in this potential range. The anodic oxidation tendencies of a number of organic compounds were explored but only hydrazine underwent oxidation at an appreciable rate. A detailed mechanistic study on the anodic oxidation of hydrazine has been carried out. The experimental data consist of potentiostatic and potentiodynamic current—potential relationships, reaction order derivatives, apparent heats of activation, and an ellipsometric investigation of the electrode surface. Based on these data and some general considerations, a mechanism is proposed in which the first charge transfer step involving a hydroxyl ion and the molecular residue of hydrazine is the rate-determining step (r.d.s.).

ChemInform Abstract: ELECTROCATALYTIC ACTIVITIES OF METAL ELECTRODES IN ANODIC OXIDATION OF HYDRAZINE IN ALKALINE SOLUTION

AbstractDie elektrolytischen Aktivitäten verschiedener Elektrodenmaterialien lassen sich mit Hilfe einer Pd‐Membranelektrode auf deren einer Seite die elektrokatalytischen Materialien abgeschieden sind, bestimmen.

Electrocatalytic activities of metal electrodes in anodic oxidation of hydrazine in alkaline solution

The electrocatalytic activities of various metals and alloys in the anodic oxidation of hydrazine in alkaline solution have been studied by means of palladium membrane method in which the contact side of the membrane was electrodeposited with a thin layer of the electrocatalytic metals. The electrode materials studied can be divided into two groups. In the first group, platinum, rhodium, cobalt, cobalt—phosphor and cobalt—boron, anodic current of hydrogen oxidation on the diffusion side decreased remarkably with an increase of the electro-oxidation of hydrazine on the contact side. The anodic oxidation of hydrazine occurs through the preliminary stepwise dehydrogenation on this group metals. On the other hand, the amount of sorbed hydrogen in the palladium, gold, nickel and nickel—phosphor electrodes increased with an increase of the electro-oxidation of hydrazine on the contact side. Thus, the anodic oxidation of hydrazine on the latter group metals may proceed through the anodic formation of the intermediate radicals which readily decompose into hydrogen and the related compounds.

Effect of the state of the surface on the electrocatalysis of the anodic oxidation of hydrazine

Effect of the state of the surface on the electrocatalysis of the anodic oxidation of hydrazine

Untersuchungen zur anodischen oxidation des hydrazins im alkalischen elektrolyten—II. Der einfluβ der wasserstoffüberspannung

Electrodes with low hydrogen overpotential such as platinum or skeleton nickel are very suitable catalysts for the anodic oxidation of hydrazine. On the other hand, there are electrodes with remarkably high hydrogen overpotential, such as amalgamated sintered nickel, on which hydrazine can be oxidised in the vicinity of the thermodynamic hydrogen potential. In contrast to the reaction on platinum, the hydrazine molecule undergoes no dehydrogenation at the amalgamated sinter nickel electrode, but the hydrogen is directly discharged without being previously split off the hydrazine molecule. The reason for this different behaviour is evidently the small heat of adsorption of hydrogen on mercury: On electrodes with high hydrogen overpotential such as amalgamated sinter nickel the heat of adsorption of hydrogen atom is not sufficiently large to split the hydrazine molecule. On electrocatalysts with low hydrogen overpotential, such as platinum or nickel, the splitting of the (N 2H 3H)-bond and, therefore, the dehydrogenation of the hydrazine molecule is energetically preferred.

Anodic oxidation of hydrazine and its derivatives: Part IV. The oxidation of methylhydrazine (MH) on gold electrodes in acid solution

The electrooxidation of methylhydrazine on a gold electrode in H 2 SO 4 has been studied. Linear sweep, steady state and quasi steady-state methods were used to evaluate the various parameters for the oxidation process and a mechanism is proposed. It involves two fast de-electronation reactions and the rate-determining step is an activated desorption step.