Aromatic polymers for advanced alkaline water electrolysis. Part I: Polyphenylene sulfide and its sulfonated derivatives

Two types of thin (0.055 cm) diaphragms, asbestos-polyphenylene sulfide and asbestos-sulfonated polyphenylene sulfide, have been obtained respectively by imbibing asbestos cardboard with polyphenylene sulfide dissolved in diphenyl sulfide and by sulfonating the polyphenylene sulfide-asbestos diaphragm with sulfur trioxide at low temperature (< 10°C). The diaphragms have been found stable in boiling KOH (30–40 w/w%) up to the end of the test period (180 h). The voltage drop across the diaphragms (Ωcm² in 43% w/w KOH: 0.21-0.5 at 30° and 0.08–0.21 at 80°C follows the order: asbestos < asbestos-sulfonatedpolyphenylene sulfide < asbestos-polyphenylene sulfide.     

Aromatic polymers for advanced alkaline water electrolysis—II. Polyphenylene sulfonic acid

Thin (0.055 cm) asbestos cardboards reinforced with sulphonated polyphenylene withstand the action of boiling 30% w/w KOH better than the plain specimen. These materials are manufactured by soaking asbestos with a solution-suspension of the sulphonated polymer in SOCI₂. With this procedure the concentration (C% w/w) of the sulphonated polymer into the asbestos host matrix and, thus, the properties of the reinforced cardboard can be modified at will. On raising C from 13 to 31% the tensile strength, water regain and electrical resistance (in 100°C 30% w/w KOH) vary from 57 to 97 kg cm^?2, 35 to 26% w/w and 0.2 to 0.56 Ω·cm² for the freshly made cardboards and from 18 to 70 kg cm^?2, 34 to 64% w/w and 0.08 to 0.40 Ω·cm² for specimens aged 20 days in boiling 30% KOH. These changes in properties are rationalized on the basis of the weight loss of the cardboard and of the changes in the MgO/SiO₂ mole ratio, IR spectra and SEM micrographs. The data suggest that, in the manufacture of the cardboard, the transfer of the organic polymer from the soaking bath into the asbestos phase depends on the physical form in which the polymer (soluble and suspended gel) is present in the bath and yields a higher concentration of polyphenylene on the surface rather than the inner layers of the cardboard. Improvements are expected from the development of more soluble sulfonated polymers.     

Effects of resin content and preparing conditions on the properties of polyphenylene sulfide resin/graphite composite for bipolar plate

In the paper, a kind of polyphenylene sulfide (PPS) resin/graphite (G) composite for bipolar plate was prepared by using the PPS resin as adhesive and simple hot pressing. The influences of the resin content, the molding temperature and holding time on the conductivity and the bending strength of the PPS/G composite bipolar plate were investigated firstly and then the optimum content and the preparing conditions of the composite were obtained. The experimental results show that the electrical conductivity decreases and the bending strength reveals a serrated variation with increase in PPS resin content; when the holding time is certain, the conductivity decreases and the bending strength increases with the molding temperature increasing. The experimental results further show that the effect of the holding time on the properties of the composite is different at different molding temperatures. The PPS/G composite with 20% PPS resin content has electrical conductivity of 118.9 S cm⁻¹ and bending strength of 52.4 MPa when it molded at 380 °C for 30 min, and has electrical conductivity of 105 S cm⁻¹, bending strength of 55.7 MPa when it molded at 390 °C for 30 min. The properties of the composites can meet the requirements of United States Department of Energy (DOE).     

Hydrogen and oxygen from water —IV. Control of an effusional separator during a solar intensity transient

An example performance map of an archetypal reactor for producing hydrogen and oxygen from water in a one-step thermochemical process is presented. We show that readjustment of the device in response to a change in incident solar intensity may be achieved, without changing the reactor temperature, Knudsen number, or feed rate, by simply changing the downstream pressure, with very little effect on the thermal efficiency.     

Synthesis and characterization of polypyrrole/carbon composite as a catalyst support for fuel cell applications

Polypyrrole (PPy)/Carbon composites were synthesized by in situ chemical oxidative polymerization of pyrrole monomer on carbon black. Effects of polymerization temperature (either 0 °C or 25 °C) and different dopants including p-toluenesulfonic acid (p-TSA) and sodium dodecyl sulfate (SDS) on the properties of the composites were investigated. The synthesized composites were characterized by XRD, FTIR and TGA. Electrical conductivities of the composites were determined by using four-point probe technique. Electrochemical oxidation characteristics of the synthesized PPy/Carbon composites were investigated by cyclic voltammetry via potential holding experiments. The PPy/Carbon composites synthesized at 0 °C and with p-TSA as dopant showed the best oxidation resistance than carbon and other composites.     

Features of solar thermochemical redox cycles for hydrogen production from water as a function of reactants’ main characteristics

Promising applications of concentrated solar energy are thermochemical cycles based on metal-metal oxide redox reactions for hydrogen production. These cycles usually consist of two steps: metal hydrolysis followed by solar reduction or thermal decomposition of the metal oxide. Thermodynamic analysis sustained by experimental results obtained for different reactants such as boron, zinc, tin and cadmium indicates that the cycle efficiency essentially depends on molar weight, valence, vapor pressure of reduced metals at reaction temperature, and strength of metal-oxygen (Me-O) bonds. Metals with lower molecular weight-to-valence ratio and stronger Me-O bonds demonstrate higher hydrogen productivity, better conversion and larger amount of heat released during the hydrolysis reaction. However, they require higher temperatures or multiple steps for the reduction of their oxides.This paper compares previously published results about these two-step processes complemented by more recent ones and describes the main aspects of selecting solid reactants to enable effective, reliable and safe operation of both the hydrolysis and the reduction steps.     

Low enthalpy geothermal fluids from the paris basin. 2—Oxidation-reduction state and consequences for the prediction of corrosion and sulfide scaling

Analytical data for redox components (sulfur, carbon and nitrogen species) in geothermal fluids are given for 45 wells of the Paris sedimentary basin. They are interpreted with a view to improving knowledge of the oxidation-reduction state of the system. Direct measurement with a platinum electrode is related to hydrogen sulfide content but does not represent the potential of the fluid within the aquifer. Computed values of apparent Nernst potentials for HS⁻ /SC₄⁻² , N₂/NH₄⁺ , CO₂ /CH₄, organic matter/CO₂, H⁺/H₂ redox couples range from −0.35 to −0.15 volts/NHE. The occurrence of mineral redox buffers is also investigated. The non-consistency of the calculated results shows that there is a lack of overall redox equilibrium in the aquifer. Despite this fact, the use of a redox parameter is discussed, in order to describe and forecast by chemical models the corrosion and scaling effects within the tubing. Pyrite, mackinawite, pyrrhotite and other iron sulfides are present. Calculations based upon nitrogen or carbon components do not allow an accurate prediction of the nature of the minerals encountered. The occurrence of microenvironments with very reducing conditions is emphasized to explain the formation of such minerals.     

Determination of the enthalpy of PCM as a function of temperature using a heat‐flux DSC—A study of different measurement procedures and their accuracy

Thermal energy storage by latent heat allows storing high amounts of energy working in narrow margins of temperature. The use of phase change material (PCM) for the latent heat storage has been studied in different applications and it has been commercialized in containers to transport blood, products sensible to temperature, to decrease their energy demand. The use of PCM in cooling and refrigeration has been attracting a lot of interest lately, but for all applications, the properties of these materials need to be known with sufficient accuracy. Regarding heat storage, it is necessary to know the enthalpy as a function of temperature. The most widely used calorimeter is the heat‐flux differential scanning calorimetry (hf‐DSC). The objective of this study is to investigate different methods for hf‐DSC analysis, namely the dynamic method and the step method, and to test their accuracy in the determination of enthalpy–temperature relationship of PCM. For the dynamic method, a strong influence of heating/cooling rate was observed. For the step method, the resulting enthalpy–temperature relationship is independent of heating/cooling rate. Commercial PCM RT27 was chosen as sample material to avoid subcooling and kinetic effects in the test measurements. The approach introduced in this study can be used to carry out similar investigations for other classes of PCM and/or other DSC instruments. Copyright © 2008 John Wiley & Sons, Ltd.     

A study of water transport as a function of the micro-porous layer arrangement in PEMFCs

Electrochemical losses as a function of the micro-porous layer (MPL) arrangement in Proton Exchange Membrane Fuel Cells (PEMFCs) are investigated by electrochemical impedance spectroscopy (EIS). Net water flux across the polymer membrane in PEMFCs is investigated for various arrangements of the MPL, namely with MPL on the cathode side alone, with MPL on both the cathode and the anode sides and without MPL. EIS and water transport are recorded for various operating conditions, such as the relative humidity of the hydrogen inlet and current density, in a PEMFC fed by fully-saturated air. The cell with an MPL on the cathode side alone has better performance than two other types of cells. Furthermore, the cell with an MPL on only the cathode increases the water flux from cathode to anode as compared to the cells with MPLs on both electrodes and cells without MPL. Oxygen-mass-transport resistances of cells in the presence of an MPL on the cathode are lower than the values for the other two cells, which indicates that the molar concentration of oxygen at the reaction surface of the catalyst layer is higher. This suggests that the MPL forces the liquid water from the cathode side to the anode side and decreases the liquid saturation in GDL at high current densities. Consequently, the MPL helps in maintaining the water content in the polymer membrane and decreases the cathode charge transfer and oxygen-mass transport resistances in PEMFCs, even when the hydrogen inlet has a low relative humidity.     

Aromatic isocyanate as a new type of electrolyte additive for the improved performance of Li-ion batteries

Aromatic isocyanate, 4-fluorophenyl isocyanate and phenyl isocyanate, were first used to reduce the initial irreversible capacities during the formation of the solid electrolyte interface (SEI) on a graphite surface. Results showed that the addition of 1–5 wt.% isocyanate to propylene carbonate-containing electrolytes could effectively reduce the initial irreversible capacities in the SEI formation and increase the cycleability of Li-ion batteries. The improvement is attributed to the high reactivity of isocyanate with chemisorbed oxygen groups, such as carboxyl and phenol, which are inevitably present in the prismatic (edge) sites of graphite and are known among the sources to cause the initial irreversible capacities of a graphite anode. It is proposed that the isocyanate reacts with carboxyl and phenol groups to form more stable products, and that the resulting products have a better affinity to the subsequently formed SEI. In addition, the presence of isocyanate assists in scavenging water and acidic HF impurities from the electrolyte.     

A study of the operating characteristics of an experimental absorption cooler using water—lithium bromide—ethylene glycol as a ternary working system

Absorption heat pumps and coolers can be satisfactorily operated using the water—lithium bromide—ethylene glycol ternary system with an ethylene glycol to water mole ratio of 1/15. This gives a high coefficient of performance and a lower risk of crystallization.     

Performance of a multi-bed adsorption heat pump using SWS-1L composite adsorbent and water as the working pair

An analysis of the coefficient of performance (COP), specific cooling power (Q_scp) and exergy losses for a four-bed adsorption heat pump is presented. A composite adsorbent (SWS-1L) and water are the adsorption pair. An optimum cycle time, corresponding to a maximum specific cooling power, was found. This maximum specific cooling power increases almost linearly with the regeneration temperature. For the operation corresponding to the maximum specific cooling power at the regeneration temperature of 120 °C, using the SWS-1L composite adsorbent to substitute a regular-density silica gel in the adsorbers, the COP and Q_scp values can be increased by 51% and 38.4%, respectively. At the regeneration temperature of 100 °C and the mode operating time of 360 s, the second-law efficiency of the adsorption heat pump is 20.4%. The cycle exergy loss mainly occurs in the adsorbers. The exergy losses in the condenser and evaporator are small. Among the four processes in the adsorbers, the precooling and preheating processes result in 41.55% and 28.96% of the cycle exergy loss, respectively, while the adsorption and regeneration processes cause 8.44% and 18.97%, respectively. The exergy losses in the precooling and preheating processes mainly result from heat transfer through a significant temperature difference.     

Utilization of biomass in the U.S. for the production of ethanol fuel as a gasoline replacement—II Energy requirements, with emphasis on lignocellulosic conversion

With relatively minor adjustments in the agricultural sector, large additional amounts of starch derived from feed corn, surplus and distressed grain, and set-aside land could presently be used for ethanol production. The quantity of ethanol that could be produced would be sufficient to replace anywhere from 5 to 27 per cent (5.5–30 billion gallons) of present gasoline requirements. Thus, the ethanol requirement for total gasohol use (10 per cent) in the U.S. could be met in the short period of time required for facility construction with no evident impact on food production. Increased supplies of ethanol will make feasible the introduction of ethanol fueled engines. High-yield sugar crops planted on new acreage could provide an additional 10 billion gal. of ethanol by the year 2000; conversion of the waste biomass from this crop to ethanol could also add substantially to this amount. Utilization of novel cellulose conversion technology can provide fermentable sugars from municipal wastes, agricultural and forest wastes, and ultimately, highly productive silvicultural operations. The wastes alone could yield over 36 billion gal. of 192° PR ethanol-fuel by the year 2000. Fast-growing woody species from silviculture are expected to yield a conservative average of 10 over-dry tons per acre per yr, convertible to 710 gal. of ethanol in a process that has 37 per cent yield. Advantages over sugar/starch crops include year-round harvesting, and use of marginal acreage. Commercial forest land presently suitable for silviculture is about 100 million acres in large tracts plus 200 million acres in small private tracts. The potential additional yield of ethanol from lignocellulosic biomass appears to be well in excess of liquid fuel requirements of an enhanced efficiency transport sector in the U.S. at present mileage demands. No conflict with food production would be necessary.     

Chemicals from biomass—the U.S. prospects for the turn of the century

Historically, chemicals from biomass have been and are expected to be economical in three major areas: byproducts, specialty items and polymers. Assessments of producing major chemicals from biomass in a processing plant based on the available conversion techniques indicate that they are not economically attractive, with the possible exception of conversion to ammonia and ethanol. The deterrents are the heavy capital investments, dependability of raw material supply and transportation costs for large plants, lack of operation experience, inadaptability to market variations, and competition from petroleum and coal. More importantly, it is also shown that even if chemicals from biomass were economical today, the resultant savings in petroleum would be far less than those achieved through other options available for the utilization of biomass as fuel and structural material. Thus, it is concluded that near-term research and development must be toward improved conversion processes, recovery of valuable products from waste streams at existing plants, more efficient use of biomass for energy and more efficient production of superior material products.     

“MINEQUA”—Part II. Carbonate equilibria in the thermal water of the Podhájska geothermal system

The MINEQUA computer program has been used to investigate carbonate equilibria in the highly mineralized thermal water of the Podhájska deep well situated in the eastern part of the Danube lowland in Czechoslovakia. Quantitative computations of water saturations with CaCO₃ are evaluated in the planned geothermal heating system, i.e. reservoir conditions, decompression, separation of dissolved gases, cooling, absorption of carbon dioxide, water reinjection and heating in the aquifer. Experimental measurements tested the relation of the pH of the water to various levels of carbon dioxide saturation at varying temperatures and partial saturation pressures. The analysis of the results determined the optimum technology for treating the thermal water that had been used for heating prior to its reinjection into the aquifer. Absorption of carbon dioxide should proceed until an equilibrium state of water saturation with CaCO₃ is established in the interval between the wellhead and the bottom of the reinjection well. The decreased scale-building capacity of the cool mineralized water should protect the casing from corrosion.     

Investigation of the potential of wind–waves as a renewable energy resource: by the example of Cesme—Turkey

There are opinions claiming that 70% of the world energy consumption could be provided from renewable resources by the year 2050. These resources are needed, because fossil fuels both cause pollution of the environment and will be depleted in the near future. In this regard, the objective of this study was to determine the wave energy potential and the costs associated with its application to Turkish waters. To this goal, the wave energy potential in Cesme–Izmir was investigated. Cesme is known to have abundant wind, which plays the primary role in the formation of sea waves. For this purpose, the Solar Energy Institute of Ege University carried out wind velocity measurements within the period from 05.11.1998 to 05.11.1999 at an altitude of 10 m in Cesme. The measured values were regarded as if they were taken at an altitude of 19.5 m from seawater level. With this approach, the Pierson–Moskowitz wave energy spectrum was constructed. Through this wave energy spectrum, wave energy that is to be obtained at the measurement area within one year was determined. The variation of wave energy according to each month was evaluated. Hence, the unit cost of electricity to be produced by a turbine (with a width of 1 m), assumed to be installed at the area of measurements, was calculated.     

‘Waste’ coir pith—a potential biomass for the treatment of dyeing wastewaters

Removal of acid dyes (acid violet and acid brilliant blue) and basic dyes (rhodamine B and methylene blue) was carried out using ‘waste’ coir pith as adsorbent. Parameters like agitation time, adsorbent dosage and pH effect were studied. Adsorption followed the first-order rate expression. The equilibrium data fit well with both Langmuir and Freundlich models of adsorption. Desorption experiments confirmed that major mode of adsorption is ion-exchange for the dyes acid brilliant blue and methylene blue whereas acid violet showed mainly physical adsorption. Chemisorption seems to be the major mode of adsorption for rhodamine B.     

Influence of the type of siliceous material used as intermediate layer in the preparation of hydrogen selective palladium composite membranes over a porous stainless steel support

In this work, several composite membranes were prepared by Pd electroless plating over modified porous stainless steel tubes (PSS). The influence of different siliceous materials used as intermediate layers was analyzed in their hydrogen permeation properties. The addition of three intermediate siliceous layers over the external surface of PSS (amorphous silica, silicalite-1 and HMS) was employed to reduce both roughness and pore size of the commercial PSS supports. These modifications allow the deposition of a thinner and continuous layer of palladium by electroless plating deposition. The technique used to prepare these silica layers on the porous stainless steel tubes is based on a controlled dip-coating process starting from the precursor gel of each silica material. The composite membranes were characterized by SEM, AFM, XRD and FT-IR. Moreover they were tested in a gas permeation set-up to determine the hydrogen and nitrogen permeability and selectivity. Roughness and porosity of original PSS supports were reduced after the incorporation of all types of silica layers, mainly for silicalite-1. As a consequence, the palladium deposition by electroless plating was clearly influenced by the feature of the intermediate layer incorporated. A defect free thin palladium layer with a thickness of ca. 5 μm over the support modified with silicalite-1 was obtained, showing a permeance of 1.423·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 and a complete ideal permselectivity of hydrogen.