Polymer anion selective membranes for electrolytic splitting of water. Part I: stability of ion-exchange groups and impact of the polymer binder

In this study, the chemical stability of three types of the anion-exchange functional groups in an alkaline environment was tested. The following groups were selected for the test: trimethylbenzylammonium, methyl pyridinium, and tributhylbenzylphosphonium. A KOH solution with various concentrations and temperatures was used as the environment. The trimethylbenzylammonium group showed the highest stability of the materials tested under conditions relevant to water electrolysis. In the next step, four types of polymeric binders, including ethylene-co-methacrylic acid, linear polyethylene, linear polyethylene blended with poly(ethylene-co-vinylalcohol), and low-density polyethylene, were selected to determine their impact on the resulting electrochemical properties of a heterogeneous membrane. This study reveals the morphology of the membrane, ion-exchange capacity, ionic conductivity, and performance in alkaline water electrolysis conducted on a laboratory scale. The material showing the most promising properties was selected for further optimization and testing.     

CoSe2@NF双功能电催化剂用于高效碱性全解水

开发用于水分解的高效稳定、低成本非贵金属电催化剂，特别是在同一电解质中对阴极的析氢反应(HER)和阳极的析氧反应(OER)都具有高效作用的电催化剂是一项挑战。以六水合硝酸钴、尿素、氟化铵和硒粉为原料，采用水热和高温固相法在镍网上原位构筑了CoSe2@NF，采用XRD、XPS、SEM和TEM对CoSe2@NF进行物相分析和形貌表征，并在碱性电解液中对CoSe2@NF的电催化析氧和析氢性能进行了测试。结果表明，表面粗糙的串珠状纳米线结构极大地增加了CoSe2有效活性位点的数量。该催化电极在OER和HER中均表现出高而稳定的催化活性。将CoSe2@NF作为全解水槽的阴阳极，在1.6 V槽电压下即可产生10 mA/cm2的电流，并可在1.7 V的电压下稳定运行100 h。这项研究为全解水提供了一种经济有效的解决方案.     

Material properties of cation exchange membranes for chloralkali electrolysis,water electrolysis and fuel cells

Owing to the development of perfluorinated ion-exchange membranes, the application of the membranes in electrochemical cells has advanced greatly, especially in chloralkali electrolysis. Material properties of perfluorinated carboxylate membranes used for chloralkali electrolysis are described in relation to the conditions of their use. Some new membranes for water electrolysis and fuel cells are briefly described.Paper presented at the meeting on Materials Problems and Material Sciences in Electrochemical Engineering Practice organised by the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineers held at Maastricht, The Netherlands. September 17th and 18th 1987.     

Nickel ferrite as inert anodes in aluminium electrolysis: Part II Material performance and long-term testing

The behaviour of three different compositions based on nickel ferrite–nickel oxide–copper cermets was investigated as anode materials in laboratory electrolysis tests for 50h in a conventional cryolite-based electrolyte. The corrosion of the anodes was assumed to be mass transfer controlled and the transfer of impurities into the electrolyte and subsequently into the cathodically deposited metal was studied. The results indicate that the materials corroded in a controlled manner. Mass transfer coefficients of species from the anode to the electrolyte were of the order of 10–4ms–1 while the mass transfer coefficients for transfer of the species from the electrolyte into the deposited metal were of the order of 10–6ms–1. Nickel exhibited significantly lower mass transfer coefficients than those of iron and copper. The extrapolated corrosion rates of the anode ranged 1.2–2.0 cm year–1, which is acceptable from an industrial perspective. The contamination of the deposited aluminium with respect to Ni and Cu was, however, too high to meet current specifications for commercial grade metal. Post-electrolysis examination of the anodes showed that a reaction layer of approximately 50m thickness was formed on the anodes. This layer did not contain any metal grains and seemed to prevent preferential corrosion of the metal phase in the underlying cermet.     

高离子电导率及CO2渗透性聚三唑盐薄膜的制备及性能

通过叠氮化合物和炔基化合物之间的Huisgen反应,结合烷基化和离子置换反应,制备了具有高离子电导率及高CO2渗透性能的新型交联型聚三唑盐薄膜.首先合成了端炔基聚四氢呋喃(DPPTMEG),利用其与双酚A二炔丙基醚(BADPE)及联苯二苄叠氮(DAMDB)间的Huisgen反应及后续的烷基化和阴离子置换反应制得新型交联...     

Polymer electrolyte membranes based on blends of sulfonated polysulfone and PEO‐grafted polyethersulfone for low temperature water electrolysis

Polymer electrolyte membranes based on blends consisting of polyethylene oxide (PEO) grafted polyether sulfone (PES‐g‐PEO) and sulfonated polysulfone (SPSF(Na)) are prepared and their electrochemical and mechanical properties are investigated with respect to water electrolysis operation. The prepared blends are amorphous; they exhibit high glass transition temperatures and high thermal stability, thus ensuring the dimensional stability under electrolysis cell operation. Because of the presence of the water soluble constituent PES‐g‐PEO, the prepared blend membranes show very high water uptakes, reaching up to 370 wt %. Membrane electrode assemblies are fabricated and evaluated in single cells demonstrating that proton conductivity depends on the PEO‐g‐PES content as well as the PEO molecular weight. Namely, the increased concentration of PES‐g‐PEO leads to increased number of charge carriers, thus result in enhanced ionic conductivity. The use of longer PEO units (MW 5000), due to their improved chain mobility, facilitates the fast proton conduction as well. The maximum proton conductivity value is achieved (1.4 × 10^?2 S cm^?1, 80°C) for the blend with the higher PEO‐g‐PES content (20 wt %) and the higher PEO molecular weight (5000). Under electrolysis cell operation, the above‐mentioned membrane with the lower ohmic resistance shows the best performance, although it is still poor mainly due to the use of Pt as anode. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39922.     

Coplanar interdigitated band electrodes for electrosynthesis. Part 4: Application to sea water electrolysis

Screen printing technology was here employed for the fabrication of interdigitated electrodes for sea water electrolysis. The anodes consisted of a ruthenium dioxide film printed on top of a thick film of platinum limiting the anodic formation of oxygen, whereas the cathodic bands are made of platinum ink. Despite the low inter-electrode gap (1 mm) and the electrode alignment, the production of hypochlorite from synthetic sea water in an agitated tank cell, could reach a current efficiency of 80% and conversion up to 30%. This geometry was found particularly suitable due to the enhanced mixing of the electrolyte between the anodes and the cathodes which resulted in a reduction of the scale deposition at the cathodes. Tarter was found to form on the cathodic bands but was rapidly released into the bulk solution, so that the array could be used over long periods of time. It has thus been shown that this cell configuration could be particularly interesting for preventing cathode passivation during electrolysis of sea water.     

Electrochemical deposition and characterization of NiFe coatings as electrocatalytic materials for alkaline water electrolysis

In this study, nickel (Cu/Ni), iron (Cu/Fe) and nickel-iron (Cu/NiFe) composite coatings with various chemical compositions were electrochemically deposited on a copper electrode and characterized using cyclic voltammetry (CV), atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques in view of their possible applications as electrocatalytic materials for the hydrogen evolution reaction (HER) in an alkaline medium. The electrocatalytic activity of the coatings for the HER was studied in 1 M KOH solution using cathodic current-potential curves and electrochemical impedance spectroscopy (EIS) techniques. The presence of nickel along with iron increases the electrocatalytic activity of the electrode for the HER when compared to nickel and iron coatings individually. The HER activity of the composite coatings depends on the chemical composition of the alloys. The Cu/NiFe-3 electrode (with a molar concentration ratio of Ni²⁺:Fe²⁺ of 4:6 in the plating bath) was found to be the best suitable cathode material for the HER in an alkaline medium under the experimental conditions studied. Furthermore, the electrocatalytic activity of the Cu/NiFe-3 electrode for the HER was tested for extended periods of time in order to evaluate the change in the electrocatalytic activity of the electrode with operation time. The HER was activation controlled and has not been changed after electrolysis. A constant current density of 100 mA cm⁻² was applied to the electrolysis system, and the corrosion behavior of the Cu/NiFe-3 electrode was investigated after different operation times using EIS and linear polarization resistance (LPR) techniques. For comparison, the corrosion behavior of a Cu/NiFe-3 electrode to which current was not applied was also investigated. The corrosion tests showed that the corrosion resistance of the Cu/NiFe-3 cathode changed when a cathodic current was applied to the electrolysis system.     

Engineering development of hyperfiltration with dynamic membranes Part II. Brackish water pretreatment pilot plant

Exploratory studies showed that feed hardness less than 10 ppm as CaCO₃ was required to maintain high fluxes (～100 gal/ft² ·day) from a dynamically formed Zr(IV)-PAA membrane. Consequently, a softening pilot plant was developed based on conventional lime-soda softening chemistry: however, because of the small scale, NaOH was substituted for lime and CO₂ was substituted for soda.The pilot plant consisted of a stirred reaction tank, a mixer-settler, and a separate filtration system containing a holdup tank, a recirculating pump, and a cross-flow filter (16 ft of fire hose jacket with a total filtration area of 4.5 ft²). Concentrated solids (18% by wt) were discharged from the mixer-settler. It was discovered that by precoating the cross-flow filter with precipitated CaCO₃, the adverse effects of Mg(OH)₂ on the rate of filtration could be ameliorated. In one test of ～300 hr duration the product from the cross-flow filter had a hardness of less than 10 ppm as CaCO₃ with an average flux of ～500 gal/ft²· day when the axial velocity was 16 ft/sec and the average pressure was 32 psig.     

Part II. Properties of the grafted and sulfonated membranes

The physical and chemical properties of polystyrene grafted and sulfonated polytetrafluoroethylene (PTFE‐graft‐PSSA) membranes prepared by radiation‐induced grafting of styrene onto commercial PTFE films using simultaneous irradiation technique followed by a sulfonation reaction are evaluated. The investigated properties include water uptake, ion exchange capacity, hydration number and ionic conductivity. All properties are correlated with the amount of grafted polystyrene (degree of grafting). The thermal stability of the membrane evaluated by thermal gravimetric analysis (TGA) is compared with that of original and grafted PTFE films. The membrane surface structural properties are analysed by electron spectroscopy for chemical analysis (ESCA). Membranes having degrees of grafting of 18 % and above show a good combination of physical and chemical properties that allow them to be proposed for use as proton conducting membranes, provided that they have sufficient chemical and mechanical stability. © 2000 Society of Chemical Industry     

Near and supercritical water. Part II: Oxidative processes

This paper is a review of applications of near and supercritical water with a focus on supercritical water oxidation (SCWO). Hydrolytic and hydrothermal reactions have been reviewed in Part I [G. Brunner, Near critical and supercritical water. Part I. Hydrolytic and hydrothermal processes, J. Supercrit. Fluids, this issue]. The potential lies in the complete destruction of persistent, anthropogenic waste material. The obstacles in the technical application are due to the highly corrosive reaction medium and the precipitation of salts. Reactor construction is the decisive feature for a commercial process. First, tank type reactors had been favored. Corrosion was kept low by ceramic material and salt deposition was avoided by a stream of cold and clean water at the reactor vessel walls. Later, tubular reactor design was preferred, and several means to prevent corrosion and salt deposits have been applied.     

Performance limits of isothermal packed bed and perforated monolithic bed reactors operated under laminar flow conditions. Part II: performance comparison and design considerations

The maximally attainable productivity of perforated monolithic bed reactors has been compared to that of the traditional packed bed of spheres for the case of laminar flow conditions and first-order isothermal reaction kinetics. Using the E number established in Part I, it could be shown in a very condensed, yet fully quantitative way that the maximal gain in total reactor productivity which can be obtained by switching from the tortuous pore system of the packed bed of spheres (large flow resistance) to the straight-running flow-through pores of a perforated monolithic bed (minimal flow resistance) typically is 25-40%. Much larger gains in total productivity can be obtained by using highly open-porous beds. Whether this high porosity is achieved using a perforated monolithic bed, a packed bed of hollow extrudates or a structured fibre-mesh bed is then only of secondary importance. The E number also allows to quantify the potential gain and the range of applicability of the more advanced reactor designs proposed in the past years (e.g., the parallel passage reactor). It could now be shown that the productivity gain of these advanced concepts can even amount up to a factor of 100. As these gains are to be realized in beds with ultra-small flow-through pores, the present study also provides a strong quantitative argument for the current research on (micro-)structured reactor beds.     

Water electrolysis under microgravity: Part II. Description of gas bubble evolution phenomena

Water electrolysis is carried out in both alkaline (25 and 2 wt.% KOH) and acidic (0.1N H₂SO₄) solutions for 8 s under a microgravity (μ-G) environment realized in a drop shaft. The effects of gravitational strength on gas bubble evolution behavior are analyzed in consideration of various factors (bubble movement, bubble assembly and single bubble). Under a μ-G environment, a collection of fine gas bubbles forms a froth layer in alkaline solutions, whereas bubbles frequently coalesce in acidic solution. Moreover, H₂ gas bubbles in alkaline jump from a cathode surface and O₂ bubbles often coalesce on an anode. In acidic solution both H₂ and O₂ bubbles frequently coalesce on electrode surfaces. Such gas bubble movements are reflected in the coalescence number and bubble residence time. A single bubble is characterized by the bubble size and the dynamic contact angle between a gas bubble and a Pt electrode, however, these factors are not essentially influenced by the gravitational strength.     

Preparation and characterization of thin films of LaNiO3 for anode application in alkaline water electrolysis

LaNiO₃ electrodes were prepared, in the form of thin films on platinum by the methods of spray pyrolysis and sequential coating of mixed metal nitrate solutions followed by thermal decomposition. The films were adherent and of p-type semiconducting. Cyclic voltammetric studies indicated the formation of a quasireversible surface redox couple, Ni(iii)/Ni(ii), on these films before the onset of oxygen evolution in 1 m KOH. The anodic Tafel slopes were 40 and 65 mV decade^–1, on the sprayed LaNiO₃ film and on the film obtained by a layer method, respectively. The reaction order with respect to OH^– was found to be 2.2 on the sprayed oxide film and 1.2 on the layer film. The sprayed oxide film was found to be electrocatalytically more active. It is suggested that the oxygen evolution reaction proceeds on both the film electrodes via the formation of the physisorbed H₂O₂ as an intermediate in the rate determining step.     

Electrochemical waste water treatment using high overvoltage anodes Part II: Anode performance and applications

The performance of highly doped SnO₂ anodes for the oxidative treatment of biologically refractory waste water was compared with PbO₂ and Pt. The oxidation of a wide range of organic compounds proceeds with an efficiency which is about 5 times higher than with platinum anodes. The oxidation efficiency was found to be independent of the pH of the water. In chloride containing media, SnO₂ anodes produce less chlorine gas than platinum anodes and hence show less potential to form hazardous chlorinated organic by-products. The design of a simple plate-and-frame reactor with undivided cells for waste water treatment using SnO₂ anodes was based on two experimental findings: (a) no interference of the cathode with the oxidation has been found: (b) the rate of oxidation is not limited by mass transfer, indicating the participation of homogeneous reactions in the overall oxidation. The new anode material reduces the specific energy requirement of electrochemical oxidation of organics in waste water to 30 to 50 kWh kg^–1 of COD removed. This makes the process an interesting alternative to chemical oxidation using oxidants such as ozone and hydrogen peroxide, or wet oxidation using oxygen at elevated temperature and pressure.     

Electrochemical preparation of cuprous oxid powder: Part II. Process conditions

Practical electrosynthesis of cuprous oxide powder was carried out on a laboratory scale in a cell specially constructed both with and without a diaphragm under the various operating conditions guided by the authors' previous research. The electrolysis was appraised in terms of the quality of the cuprous oxide product, the electrodissolution of the copper anode, and the SEM microstructure of the cuprous oxide powder. In a cell having a diaphragm, of which nylon fabric is the best, the optimal electrolysis operating conditions are: 250gl^–1 NaCl, 0.1–1.0gl^–1 NaOH, 500–1500Am^–2, 80°C, perforated titanium sheet as the cathode, and around 3% cell volume of electrolyte circulation per minute. Under these conditions a product containing more than 97% cuprous oxide can easily be produced with very stable electrolysis and quite uniform dissolution of the copper anode. To eliminate the use of a diaphragm in the cell, the addition of sodium chromate, sodium dichromate, or calcium gluconate is effective in a sense, depending upon the requirements of the cuprous oxide product. For a product in which more than 95% cuprous oxide and no copper powder are required but a slightly higher content of chloride is allowable, sodium chromate and dichromate can be proposed for use with the former around 0.03–0.05gl^–1 and the latter around 0.020–0.025gl^–1, although the copper anode will not be perfectly evenly dissolved. For a product in which more than 97% cuprous oxide is demanded and a very small amount of copper powder is tolerated, calcium gluconate would be acceptable at around 4.5gl^–1 with quite even dissolution of the copper anode. As to the auxiliary additives, hydrazine hydrate has a negative effect on the quality of the cuprous oxide product. Sucrose can cause a small increase in the chloride content but can make the particles of cuprous oxide more compact thereby increasing sharply its apparent density. Hydroxylamine hydrochloride is the best auxiliary additive which has a positive effect on the purity of the cuprous oxide product but produces no obvious change in the microstructure on the cuprous oxide particles. Even though most work has been concentrated on the electrolytic process, the subsequent processes are equally important: 65–70°C, distilled water for washing, benzotriazole in ethanol solution for stabilization of the cuprous oxide, and 100°C at a vacuum of less than 20mm Hg for drying seem to be satisfactory. A vacuum drying temperature of 55–60°C may be more appropriate to ensure against any oxidation of the product.     

Optimization of injection molding design. Part II: Molding conditions optimization

The quality of an injection molded part is affected by many factors. These include geometric parameters associated with the mold design and the cooling system design as well as process parameters such as the molding conditions during the filling phase. In the companion paper, the problem of automatic optimization of gate location was addressed. In this paper, a methodology for molding condition optimization is presented. The optimization problem can be broken into three parts. An approximate feasible molding space (AFMS) is first determined to constrain the search space for the optimization algorithm. Quality is quantified as a function of flow simulation outputs and constitutes the objective function that must be minimized. The resulting optimization is solved by iterative search in the constrained space based on numerical optimization algorithms. The proposed methodology is not dependent on any particular simulation package and may be applied for any thermoplastic material and any complex mold geometry.     

Development of high performance,waterborne coatings. Part II: Factors affecting adhesion performance

A new manufacturing process for high performance, waterborne coatings for can coating application was developed, which includes emulsification of an epoxy resin with or without a hardener by incorporation of an acrylic resin. It is possible by this new process to emulsify a variety of resins with minimum effects of the surfactant. (acrylic resin). The effects of surfactant and neutralizer on adhesion performance were studied. It was found that the effects of the acrylic resin amount were relatively small, and that the effects of the neutralizer were significant. It was confirmed that the usage of ammonia or amines with a branched alkyl group is required to achieve balanced dry and wet adhesion.     

Diffusion of lignin macromolecules within the fibre walls of kraft pulp. Part I: Determination of the diffusion coefficient under alkaline conditions

The intrinsic rate of diffusion of soluble lignin from fibre walls to bulk liquor has never been determined previously because of experimental difficulties; for example, the diffusion rate determined in a stirred cell is affected by the mechanical action of stirring. In our work, the intrinsic rate of diffusion of lignin macromolecules from the fibre walls of a softwood kraft pulp was determined under alkaline conditions using a displacement cell which eliminated external heat and mass transfer resistances and pulp fibre disturbances. The effects of such experimental conditions as pulp bed height and liquid flow rate were studied. The diffusion rate can be described by a diffusion model for a hollow cylinder with a very wide range of diffusion coefficients. The diffusion rate increased with increasing pH. Our results provide a new understanding of the lignin diffusion process in fibre walls, which is affected by the size of lignin molecules and the pores, and by the electrostatic interactions between intrafibre pore walls and lignin.     

Particle formation under monomer-starved conditions in the semibatch emulsion polymerisation of styrene. Part II. Mathematical modelling

Models, together with a comparison with experimental data, are presented for the particle nucleation under monomer-starved conditions. In the first model, simplifications were made to obtain analytical solutions. The Smith and Ewart theory was extended to include particle formation under monomer-starved conditions. It was assumed that the rate of particle growth is controlled by the rate of monomer addition. An appropriate correlation for prediction of number of polymer particles in terms of surfactant and initiator concentrations and monomer addition rate was derived as N_p=k(a_s[S])^1.0R_I^2/3R_a^−2/3. The second model takes advantage of the new developments in understanding of the kinetics of the water phase and its effects on the radical capture efficiency of micelles. The model accounts for monomer solubilisation in the micelles. According to the model predictions, the size of micelles and their aggregation number are subject to variation during nucleation. The model could successfully predict some important features of particle formation under monomer-starved conditions.