Raney nickel activated H2-cathodes Part II: Correlation of morphology and effective catalytic activity of Raney-nickel coated cathodes

Raney nickel activated hydrogen-cathodes obtained by caustic leaching of cathodically deposited Ni/Zn precursor alloy coatings on nickel substrates were investigated with respect to their effective catalytic activity. Important factors influencing this activity are the surface specific amount of the inner surface of the Raney nickel coatings and, in particular, the tertiary structure of the catalyst coating. Coarse pores and cracks are developed during leaching of the Ni/Zn precursor which, due to unsteady deposition conditions, show a layered structure. These cracks are essential for a high catalytic activity, since micropores of Raney nickel coatings are utilized to pore depths of no more than 10 m. The generation of layered structures of the coatings with changing zinc content, which is experienced by Ni/Zn codeposition from acidic solutions, is influenced by a number of process parameters. The most important parameter is the cathode potential which may fluctuate strongly during cathodic deposition of the Ni/Zn precursor coatings due to minute temperature and/or pH changes.     

Cathodic behaviour of IrO2 electrodes in alkaline solution Part I: Electrochemical surface characterization

IrO₂ electrodes prepared by thermal decomposition of IrCl₃ on a titanium support at temperatures of calcination between 300 and 500°C have been characterized by cyclic voltammetry and potential steps. Standard voltammetric curves have been recorded between –0.65 and 0.35 V vs SCE (prior to H₂ and O₂ evolution) as a fingerprint of the surface state, and the associated charge,q ^*, has been used to monitor the morphology of the active layer. The effect of hydrogen evolution has been investigated by progressively decreasing the negative potential limit, and by increasingly holding the electrode under hydrogen evolution at a constant potential. Phenomena of proton penetration beneath the outer surface into an inner surface have been quantified by potential step experiments. The effect of storing the electrodes in water rather than in the open air has also been investigated. The thermal oxides lose their typical features at calcination temperature < 350° C. Cathodic load does not appear to cause macroscopic modifications of the surface state.This paper is dedicated to Professor Brian E. Conway on the occasion of his 65th birthday, and in recognition of his outstanding contribution to electrochemistry.     

Discharge behaviour of tubular lead dioxide electrodes Part III: Two-dimensional current density distribution

The initial current density distribution in lead acid batteries with tubular lead dioxide electrodes and flat lead electrodes has been studied by means of a two-dimensional model and experimental verification by polarization curves and potential transients during galvanostatic discharge. The cell geometry was modelled with and without separators and a tubular electrode envelope. The governing equations were solved with a finite element method. It was found that the tube envelope has a large impact on the current density distribution and had to be incorporated into the model to fit the experimental results. Although the envelope increases the ohmic losses, it has the positive effect of giving a more uniform current distribution around the electrode tube. A lead acid cell with tubular positive electrodes and flat negative electrodes can therefore be approximated by a one-dimensional model consisting of a positive electrode tube placed concentrically in a cylindrical lead electrode. The two-dimensional model was further used to study the effects of different design factors, for example, cell width and kinetic parameters of the lead dioxide electrode.     

Aluminium alloys in sulphuric acid Part I: Electrochemical behaviour of rotating and stationary disc electrodes

Anodic oxidation of various aluminium alloys was investigated by means of rotating disc electrodes in 3 M H₂SO₄ as a function of Cl^–, F^–, Zn²⁺ and In³⁺ concentration. Al-In, Al-Zn/In and Al-Zn/Sn alloys yielded current-potential curves at the lowest overpotentials and faradaic efficiencies for anodic oxidation of up to 98% at currents 50 mA cm^–2. While these alloys were electrochemically active in the presence of chloride as the only additive in sulphuric acid, binary aluminium alloys with Ce, Ga, La, Nd, Sn, Ta, Te, Ti or Tl were only active when Cl^–, Zn²⁺ and In³⁺ species were added to the electrolyte. With the exception of Al-Ga, binary alloys displayed high faradaic efficiencies of up to 95%. Fluoride additives resulted in current-potential curves at even more negative potentials than those with chlorides. In contrast to Cl^–, fluoride ions are consumed during the aluminium oxidation process due to complexation with Al(III).     

Modelling of water adsorption by activated carbons: effects of microporous structure and oxygen content

The present paper examines the adsorption of water by microporous carbons containing various amounts of surface oxygen and a smaller proportion of basic centres. The modelling of water adsorption for 293 and 310 K, using variable pore size distributions (PSD), confirms that the overall type IV isotherm is the sum of a type I isotherm associated with the specific interactions, and a type V isotherm reflecting the non-specific interactions. The principle of temperature invariance is followed by these isotherms, which indicates that modelling leads to the Dubinin-Astakhov equation.The present approach allows the prediction of water adsorption near room temperature, on the basis of the PSD and the density of oxygen present on the surface area of the micropores. It is assumed, to a first and good approximation, that the pores are slit-shaped and the oxygen distribution is random.     

Powdered activated carbon and carbon paste electrodes: comparison of electrochemical behaviour

Commercial activated carbon (Norit R3ex), de-mineralised with conc. HF and HCl, was oxidised (conc. HNO₃) and heat-treated at various temperatures (180, 300 and 420 °C). The physicochemical properties of the samples obtained were characterised by selective neutralisation and pH-metric titration of surface functional groups (acid–base properties), thermogravimetry (thermal stability—TG), FTIR spectroscopy (chemical structure) and low-temperature nitrogen adsorption (BET surface area). Thermal treatment of the carbon materials caused the surface functional groups to decompose; in consequence, the chemical properties of the carbon surfaces changed. Cyclic voltammetric studies were carried out on all samples using a powdered activated carbon electrode (PACE) and a carbon paste electrode (CPE), as were electrochemical measurements in aqueous electrolyte solutions (0.1 M HNO₃ or NaNO₃) in the presence of Cu²⁺ ions acting as a depolariser. The shapes of the cyclic voltammograms varied according to the form of the electrodes (powder or paste) and to the changes in the surface chemical structure of the carbons. The electrochemical behaviour of the carbons depended on the presence of oxygen-containing surface functional groups. The peak potentials and their charge for the redox reactions of copper ions depended on their interaction with the carbon surface.     

Electrosynthesis of toluidines using thermally coated Ti/TiO2 electrodes

Cyclic voltammetric and preparative scale investigations on the electroreduction of (o-nitrotoluene (ONT), m-nitrotoluene (MNT), p-nitrotoluene (PNT) and 2,4-dinitrotoluene (DNT) to their corresponding toluidines in 1 m H₂SO₄ using thermally coated Ti/TiO₂ electrode are reported. In the cyclic voltammetric time scales inhibitive adsorption which decreased in the order i _p ONT > i _p MNT > i _p PNT > i _p DNT was noticed. The heterogeneous redox catalytic currents were also found to decrease in the same order. In preparative electrolysis, these inhibitive effects became unimportant. Yields around 90% were achieved for all four nitro compounds. The thermally coated Ti/TiO₂ electrode could be reused at least five times without any loss in yield and current efficiency.     

Network analysis of packed-bed activated carbon electrodes with linear I/V-graphs

Granular activated carbon (GAC) filtration is an important step in the purification of surface water. However, charcoal causes corrosion of steel in water when there is an electrical contact between the two. For many carbons it is now possible to discuss the instantaneous voltage behaviour of the GAC bed under these conditions. Most GAC packed-bed electrodes show linear I/V-graphs. In this case the GAC bed can be treated as a four-terminal network. With the aid of network theory the voltage behaviour under a great variety of electrical conditions can be discussed. The method, device and evaluation process are described.     

An electrochemical technique for the reduction of aromatic nitrocompounds in H2SO4 medium on thermally coated Ti/TiO2 electrodes

An outline of the recently developed preparative method for the electroreduction of aromatic nitro-compounds using thermally coated Ti/TiO₂ electrodes in H₂SO₄ medium is presented. The method of preparation of stable and electrochemically active Ti/TiO₂ electrode is described. Cyclic voltammetry indicates wide variations in the heterogeneous redox catalysis of different aromatic nitro-compounds. Weak adsorption blocking due to insoluble film formation, catalytic hydrogen evolution and strong pH sensitive reactant adsorption effects are illustrated. Optimum conditions for the preparative scale electroreduction of these nitrocompounds are presented. The yields and current efficiencies were uniformly high for all the nitrocompounds involved. In addition to heterogeneous redox catalysis active hydrogen generated at the electrode surface also probably acts as efficient reducing agent on the preparative time scale. Reuse of electrolyte and stability of electrodes during prolonged electrolysis are also reported.     

Electrosynthesis at oxide coated electrodes Part 1 the kinetics of ethanol oxidation at spinel electrodes in aqueous base

The oxidation of ethanol at Ni/Co spinel coated electrodes in aqueous base has been investigated. It is shown that these electrodes are very stable and have a good catalytic activity for the conversion of ethanol to acetic acid (for example 24 mA cm^–2 for the oxidation of 0.1 mol dm^–3 ethanol), far superior to the nickel anodes previously used for the reaction in similar conditions. TheI-E curve for the oxidation of ethanol at a spinel shows a well formed wave prior to oxygen evolution at a potential where the spinel surface itself undergoes oxidation. The limiting current is partially mass transport controlled. The influence of the electrolysis conditions, the composition of the spinel coated electrodes and of parameters in their preparation, on the rate of ethanol oxidation is described.     

Modelling and calculation of the current density distribution evolution at vertical gas-evolving electrodes

During industrial electrolysis, for hydrogen, dichloride or aluminium production, there is bubbles creation at one or two electrodes which imply a great hydrodynamic acceleration but also a quite important electrical field disturbance. This disturbance can lead to the modification of the local current density and to anode effects for example. There is few works concerning the local modelling of coupled electro active species transport and electrochemical processes in a biphasic electrolyte. There are also few local experimental measurements in term of chemical composition, temperature or current density which would allow the numerical calculations validation. Nevertheless, effects like the anode effect, particularly expensive on the point of the process efficiency, should need a better understanding. Nowadays, the respective roles of the local temperature increases, the electro active specie composition or the transport properties modification due to bubbles are not known.The goal of the present work is the modelling and the numerical simulation of the vertical electrode configuration for a biphasic electrolysis process. Bubbles presence is supposed to modify the electrical properties, and then the electro active species diffusive transport and the current density. Bubbles are also motion sources for the electrolysis cell flow, and then hydrodynamic properties are strongly coupled with species transport and electrical field. The present work shows hydrodynamic and electrical properties in a laboratory scale electrolysis cell with a vertical electrode. The numerical algorithm used was the finite volume used in the computational fluid dynamic software Fluent^®.     

Simulation of CO2/CH4 high pressure separation on microporous activated carbon

Abstract

Pure component adsorption equilibrium of CH₄ and CO₂ on activated carbon have been studied at three different temperatures, 298, 323, and 348?K within a pressure range of 10–2000?kPa. Binary adsorption equilibrium isotherm was described using extended Sips equation and ideal adsorbed solution theory (IAST) model. Experimental breakthrough curves of CO₂/CH₄ (40:60 in a molar basis) were performed at four different pressures (300, 600, 1200, and 1800?kPa). The experimental results of binary isotherms and breakthrough curves have been compared to the predicted simulation data in order to evaluate the best isotherm model for this scenario. The IAST and Sips models described significantly different results for each adsorbed component when higher pressures are set. These different results cause a significant discrepancy in the estimation of the equilibrium selectivity. Simulated and experimental equilibrium selectivity data provided by IAST presented values of around 4, for CO₂/CH₄, and extended Sips presented values of around 2. Also, simulated breakthrough curves showed that IAST fits better to the experimental data at higher pressures. According to the simulations, in a binary mixture at total pressure over 800?kPa, extended Sips model underestimated significantly the CO₂ adsorbed amount and overestimated the CH₄ adsorbed amount.     

SO2 retention on CaO/activated carbon sorbents. Part I: Importance of calcium loading and dispersion

Sorbents for SO₂ retention at low temperature consisting of CaO supported on activated carbons have been prepared by different methods (physical mixing, incipient wetness impregnation, rotary evaporator impregnation, complex formation and ionic exchange). Ca(OH)₂, CaCO₃, CaO, Ca(CH₃COO)₂ and Ca(C₂H₅COO)₂ have been used as calcium precursors. The preparation method affects calcium loading as well as calcium dispersion. SO₂ retention depends both on the calcium loading and on the calcium dispersion. The best preparation method, among those tested, was impregnation of the activated carbon with calcium acetate. Similar calcium loading can be obtained by the physical mixing method but the resulting calcium dispersion is low. On the contrary, samples with higher calcium dispersion were obtained by the complex formation method, presenting the disadvantage of the low calcium loading reached. The molar calcium conversion results are much higher than values reported for unsupported calcium compounds.     

Preparation and properties of Raney nickel electrodes on Ni-Zn base for H2 and O2 evolution from alkaline solutions Part II: Leaching (activation) of the Ni-Zn electrodeposits in concentrated KOH solutions and H2 and O2 overvoltage on activated Ni-Zn Raney electrodes

The partial dissolution of zinc from electrodeposited Ni-Zn alloys (withX _Zn ⁰ =22–87.3 mol %) was studied, in cold and nearly boiling 10m KOH. It was found that alloys withX _Zn ⁰ 22 mol % are not dissolved at all. The dissolved zinc fraction,A, increased rapidly with further increase in zinc content and after having passed a maximum withA=82–90% atX _Zn ⁰ =55–58 mol % and a sharp minimum withA=52–65% atX _Zn ⁰ =65–69 mol %, it asymptotically approached toA 100% atX _Zn ⁰ 100 mol %. The discontinuous dependence ofA againstX _Zn ⁰ may be explained by differences in the crystallographic composition of the alloy deposits. Alloys withX _Zn ⁰ <50–60 mol % can be allocated to solid solutions of zinc in the Ni matrix (-phase); the range of 50–60<X _Zn ⁰ <70–80 mol % corresponds to the coexistence of + phases. The pure -phase exists within a narrow range atX _Zn ⁰ =75–80 mol %. No zinc dissolution from Ni-Zn alloys withX _Zn ⁰ 22 mol % was explained by extremely low zinc activities in dilute solid solutions of the -phases shifting the Gibbs energy of the dissolution reaction to very low negative, or even to positive values. The dependence of the hydrogen and oxygen overvoltage atj=0.4 A cm^–2 in 10m, KOH at 100°C on the original zinc contentX _Zn ⁰ showed, in both cases, a clear minimum atX _Zn ⁰ =75–78 mol %. This points to a practically pure -phase in the original Ni-Zn alloy with an approximate composition NiZn₃.     

Modelling of through-hole electrodeposition Part I: Effect of electrical migration

A quantitative investigation was conducted on the effect of electrical migration on the current distribution in through-hole electrodeposition. Polarization, surface concentration and current distribution were computed as functions of the geometry of the through-hole, electrolyte flow rate, applied current density and concentration of the supporting electrolyte. Results were compared with those from a simplified model in which the electric field was neglected within the diffusion layer.     

SO2 retention on CaO/activated carbon sorbents. Part II: Effect of the activated carbon support

The present paper analyses the role of the activated carbon (AC) properties on the SO₂ uptake capacity of CaO/AC sorbents prepared by AC impregnation or ionic exchange with calcium acetate water solutions. Gas adsorption and mercury porosimetry have been used for textural characterization of the AC and surface oxygen groups have been characterized by temperature programmed desorption (TPD). Thermogravimetry has been used for SO₂ retention tests and CO₂ chemisorption at 300 °C for CaO dispersion (d) determinations. The results show that the surface calcium on CaO/AC samples, determined as “Ca loading · CaO dispersion” (parameter Ca(%) · d), governs the SO₂ uptake. The surface oxygen content is the AC property that mainly controls both the calcium loading and surface calcium on CaO/AC samples, which could be explained by the fact that the surface oxygen lowers the hydrophobic character of the AC supports therefore favouring the interaction with the calcium acetate water solutions. The combination of high calcium loading and dispersion leads to SO₂ uptakes up to 123 mg SO₂/g. The textural properties of the supports have some influence in the calcium loading. However, the effect is masked by the blockage of AC porosity by the calcium loaded.     

In Vitro/In Vivo Translation of Synergistic Combination of MDM2 and MEK Inhibitors in Melanoma Using PBPK/PD Modelling: Part I

Translation of the synergy between the Siremadlin (MDM2 inhibitor) and Trametinib (MEK inhibitor) combination observed in vitro into in vivo synergistic efficacy in melanoma requires estimation of the interaction between these molecules at the pharmacokinetic (PK) and pharmacodynamic (PD) levels. The cytotoxicity of the Siremadlin and Trametinib combination was evaluated in vitro in melanoma A375 cells with MTS and RealTime-Glo assays. Analysis of the drug combination matrix was performed using Synergy and Synergyfinder packages. Calculated drug interaction metrics showed high synergy between Siremadlin and Trametinib: 23.12%, or a 7.48% increase of combined drug efficacy (concentration-independent parameter β from Synergy package analysis and concentration-dependent δ parameter from Synergyfinder analysis, respectively). In order to select the optimal PD interaction parameter which may translate observed in vitro synergy metrics into the in vivo setting, further PK/PD studies on cancer xenograft animal models coupled with PBPK/PD modelling are needed.     

Electrochemical behaviour of polyacrylic acid coated gold electrodes: An application to remove heavy metal ions from wastewater

An efficient and low cost preparation method (Diazonium-Induced Anchoring Process) to graft polyacrylic acid (PAA) on the gold substrate has been reported. IR, XPS and AFM techniques were used to characterize the obtained polymer film. The interfacial electrochemistry of the PAA coated gold electrodes was studied by means of impedance spectroscopy and cyclic voltammetry transition techniques. The ability of PAA-grafted onto a gold electrode to reversibly bind or release metal ions was confirmed. As a broad-range chelating material, PAA is able to capture several heavy metal ions at low concentration. The release of those metal ions from the grafted PAA film was obtained under electro-induced-acidification by applying an anodic potential at the electrode to promote a localized water electrolysis. Application of electrochemical-pH-switchable PAA films can be considered within the field of heavy metal waste treatments.     

Carbon electrodes: Part 2. The anodic oxidation of N-propylamine

The anodic oxidation of a primary aliphatic amine, n-propylamine, has been studied at electrodes of vitreous carbon and pyrolytic graphite. The electrode reaction has been found to differ greatly for the two materials, as evidenced by the voltammetric behaviour at rotating disc electrodes and the results of preparative electrolyses. The observations at the vitreous carbon electrode are in agreement with the mechanism proposed by Mann and Barnes for the oxidation of propylamine at a stationary platinum electrode. A novel mechanism is proposed for the oxidation at a pyrolytic graphite anode.Part 1 M. P. J. Brennan and O. R. Brown,J. Appl. Electrochem.,2 (1972) 43.