Study of the influence of the amount of PBI–H3PO4 in the catalytic layer of a high temperature PEMFC

The influence of the amount of polybenzimidazole (PBI)-H₃PO₄ (normalized with respect to the PBI loading, which expressed as C/PBI weight ratio) content in both the anode and cathode has been studied for a PBI-based high temperature proton exchange membrane (PEM) fuel cell. The electrodes prepared with different amounts of PBI have been characterized physically, by measuring the pore size distribution, and visualizing the surface microstructure. Afterwards, the electrochemical behaviour of the electrodes has been evaluated. The catalytic electrochemical activity has been measured by voltamperometry for each electrode prepared with a different PBI content, and the cell performance results have been studied, supported by the impedance spectra, in order to determine the influence of the PBI loading in each electrode. The best results have been achieved with a C/PBI weight ratio of 20, for both the anode and the cathode. A lower C/PBI weight ratio (larger amount of PBI in the catalytic layer) reduced the electrocatalytic activity, and impaired the mass transport processes, due to the large amount of polymer covering the catalyst particle, lowering the cell performance. A higher C/PBI weight ratio (lower amount of PBI in the catalytic layer) reduced the electrocatalytic activity, and slightly increased the ohmic resistance. The low amount of the polymeric ionic carrier PBI–H₃PO₄ limited the proton mobility, despite of the presence of large amounts of “free” H₃PO₄ in the catalytic layer.     

Effect of sulfites on the performance of LiBOB/γ-butyrolactone electrolytes

γ-Butyrolactone (GBL) increases the irreversible capacity of lithium ion battery when it is employed as the solvent for the lithium bis(oxalate)borate (LiBOB)-based electrolyte. To solve this problem, four sulfites are introduced to the electrolyte. The effects of ethyl sulfite (ES), propylene sulfite (PS), dimethyl sulfite (DMS) and diethyl sulfite (DES) on the LiBOB/GBL-based electrolytes are studied. The ionic conductivity, electrochemical stability, cycle performance and thermal stability of the sulfite containing electrolytes are tested and compared with that of the common electrolyte and the 1 M LiBOB/GBL electrolyte. The results indicate that the cyclic sulfites ES and PS show little benefit to the performance of the electrolyte. However, the linear sulfites DMS and DES could increase the ionic conductivity of the electrolyte and form an effective SEI film on the anode surface. In particular, the 1 M LiBOB/GBL + DMS (3:1 wt.) electrolyte mitigates the irreversible capacity and enhances the first coulomb efficiency and the capacity retention. The thermal stability of the DMS containing electrolyte is also improved and is better than that of the common electrolyte. These beneficial effects make them possibly to be a promising cosolvent for the LiBOB/GBL electrolyte.     

Benchmarking of the pre/post-combustion chemical absorption for the CO2 capture

The aim of the article was to compare the pre- and post-combustion CO₂ capture process employing the chemical absorption technology. The integration of the chemical absorption process before or after the coal combustion has an impact on the power plant efficiency because, in both cases, the thermal energy consumption for solvent regeneration is provided by the steam extracted from the low pressure steam turbine. The solvent used in this study for the CO₂ capture was monoethanolamine (MEA) with a weight concentration of 30%. In the case of the pre-combustion integration, the coal gasification was analysed for different ratios air/fuel (A/F) in order to determine its influences on the syngas composition and consequently on the low heating value (LHV). The LHV maximum value (28 MJ/kg) was obtained for an A/F ratio of 0.5 kg_air/kg_fuel, for which the carbon dioxide concentration in the syngas was the highest (17.26%). But, considering the carbon dioxide capture, the useful energy (the difference between the thermal energy available with the syngas fuel and the thermal energy required for solvent regeneration) was minimal. The maximum value (61.59 MJ) for the useful energy was obtained for an A/F ratio of 4 kg_air/kg_fuel. Also, in both cases, the chemical absorption pre- and post-combustion process, the power plant efficiency decreases with the growth of the L/G ratio. In the case of the pre-combustion process, considering the CO₂ capture efficiency of 90%, the L/G ratio obtained was of 2.55 mol_solvent/mol_syngas and the heat required for the solvent regeneration was of 2.18 GJ/tCO₂. In the case of the post-combustion CO₂ capture, for the same value of the CO₂ capture efficiency, the L/G ratio obtained was of 1.13 mol_solvent/mol_{flue gas} and the heat required was of 2.80 GJ/tCO₂. However, the integration of the CO₂ capture process in the power plant leads to reducing the global efficiency to 30% in the pre-combustion case and to 38% to the post-combustion case.     

Optimization of the interface polarization of the La2NiO4-based cathode working with the Ce1–xSmxO2–δ electrolyte system

The performance of La₂NiO₄ cathode material and Ce_1–xSm_xO_2–δ (x = 0.1, 0.2, 0.3, 0.4) electrolyte system was analyzed. Ceria-based materials were prepared by the freeze-drying precursor route whereas La₂NiO₄ was prepared by the nitrate–citrate procedure. Electrolyte pellets were obtained after sintering the powders at 1600 °C for 10 h. Also dense ceria-based electrolytes samples were obtained by calcining the powders at 1150 °C after the addition of 2 mol%-Co. Interface polarization measurements were performed by impedance spectroscopy in air at open circuit voltage, using symmetrical cells prepared after the deposition of porous La₂NiO₄-electrodes on the Ce_1–xSm_xO_2–δ system. X-ray diffraction (XRD) of cathode materials after using in symmetrical cells confirmed no significant reaction between La₂NiO₄ and ceria-based electrolytes. The efficiency of the cathode material is highly dependent on the composition of the electrolyte, and low-content Sm-doped ceria samples revealed an important decrease in the performance of the system. Differences in electrochemical behaviour were attributed principally to the oxide ion transference between cathode and electrolyte, and were correlated to the conductivity of the electrolyte. In this way cobalt-doped electrolytes with a Sm-content ≤30% perform better than free-cobalt samples due to the increase in grain boundary conductivity. Finally, composites of the ceria-based materials and La₂NiO₄ to use as cathode were prepared and an important increase of the interface performance was observed compared to La₂NiO₄ pure cathode. Predictions of maximun power density were obtained by the mixed transport properties of the electrolytes and by the interface polarization results. The use of composite materials could allow to increase the performance of the cell from 170 mW cm⁻² for pure La₂NiO₄ cathode, to 370 mW cm⁻² for La₂NiO₄–Ce_0.8Sm_0.2O_2–δ cathode, both working with Ce_0.8Sm_0.2O_2–δ electrolyte 300 μm in thickness and Ni–Ce_0.8Sm_0.2O_2–δ as anode at 800 °C.     

Effect of the catalyst composition in the Ptx(Ru–Ir)1−x/C system on the electro-oxidation of methanol in acid media

The effect of variations in the composition for ternary catalysts of the type Pt_x(Ru–Ir)_1−x/C on the methanol oxidation reaction in acid media for x values of 0.25, 0.50 and 0.75 is reported. The catalysts were prepared by the sol–gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption spectroscopy (AAS) and energy dispersive X-ray (EDX) analyses. The nanometric character (2.8–3.2 nm) of the sol–gel deposits was demonstrated by XRD and TEM while EDX and AAS analyses showed that the metallic ratio in the compounds was very near to the expected one. Cyclic voltammograms for methanol oxidation revealed that the reaction onset occur at less positive potentials in all the ternary catalysts tested here when compared to a Pt_0.75–Ru_0.25/C (E-Tek) commercial composite. Steady-state polarization experiments (Tafel plots) showed that the Pt_0.25(Ru–Ir)_0.75/C catalyst is the more active one for methanol oxidation as revealed by the shift of the reaction onset towards lower potentials. In addition, constant potential electrolyses suggest that the addition of Ru and Ir to Pt decreases the poisoning effect of the strongly adsorbed species generated during methanol oxidation. Consequently, the Pt_0.25(Ru–Ir)_0.75/C composite catalyst is a very promising one for practical applications.     

Effect of alumina on the enhancement of hydrogen production and the reduction of hydrogen peroxide in the γ-radiolysis of pure water and 0.4 M H2SO4 aqueous solution

The H₂ and H₂O₂ produced by ⁶⁰Co γ-radiation at room temperature were measured in pure water and 0.4 M H₂SO₄ aqueous solution with alumina powder. By increasing the addition of alumina powder, a strong reduction of H₂O₂ concentrations in the solutions was obtained, and the final product H₂ yields were correspondingly enhanced. These enhancement and reduction effects were diminished in the subsequent γ-radiation when irradiated alumina powder was used. The effects were reversibly restored by washing the irradiated powder with purified water. In 0.4 M H₂SO₄ solution with alumina powder, the H₂ yields increased by increasing the absorbed dose rate in the region of 1-5 kGy/h. The radiation-enhanced H₂ production correlated with the reduction of H₂O₂ concentration could be brought about by the reduction of H₂O₂ molecules and OH radicals in the solutions due to alumina powder.     

Synthesis of an active and stable Ptshell–Pdcore/C catalyst for the electro-oxidation of methanol

A Pt_shell–Pd_core/C catalyst is prepared via electroless deposition and galvanic displacement. The catalyst is active toward the electro-oxidation of methanol and is more stable against CO_ad-poisoning than a commercial Pt/C catalyst. The stable activity of Pt_shell–Pd_core/C is ascribed to the tuned electronic property of the Pt over-layer in the Pt_shell–Pd_core/C, which leads to weak binding with CO_ad and increases the kinetics of OH_ad formation. The weakened binding property of the surface Pt with CO_ad and the facile oxidation of CO_ad by OH_ad were confirmed by a spectroscopic analysis and in a CO_ad-stripping experiment, respectively. The electro-oxidation of CO_ad by OH_ad is the rate-determining step of methanol oxidation. Therefore, the accelerated formation of OH_ad contributes to the overall oxidation reaction, preventing CO_ad-poisoning. In addition, Pt_shell–Pd_core/C maintains its activity longer than Pt/C does during a prolonged cycle experiment.     

A mechanism of ultraviolet activation of the α-AlH3 decomposition

We investigated the mechanism of activation of α-AlH₃ powder decomposition by irradiation with ultraviolet (UV) light using barometry, photoluminescence (PL), cathode luminescence (CL) and X-ray diffraction (XRD) methods. Exposing the samples under a mercury lamp through the filters we have shown that only the line, corresponding to the energy of 4.88 eV, leads to activation, whereas the spectral lines of lower energy are ineffective. XRD shows that after continued UV activation the aluminum clusters with metallic properties are formed on the surface of the AlH₃ powder particles at room temperature. The analysis of results of performed calculations of the absorption spectrum of the perfect crystal α-AlH₃ using DFT method showed that hydrogen vacancies are involved in activation by UV light. Studying of dynamics of CL and PL spectra at different UV expositions permitted to suggest the following mechanism of activation. Absorption of a photon implies that vacancy captures an electron from a neighboring hydrogen atom. Hydrogen atom then can leave its regular position in the lattice and form a new vacancy next to the first. Clustering of vacancies occurs. Continued UV activation is accompanied by merging of vacancies, which deprives the aluminum atoms of hydrogen bonds connecting them. Thus the aluminum clusters with metallic properties are formed.     

Electrocatalytic properties for the hydrogen evolution of the electrodeposited Ni–Mo/WC composites

The catalytical activity for the hydrogen evolution reaction (HER) of the electrodeposited Ni–Mo/WC composites is examined in 1 M KOH solution. The structure, surface morphology and surface composition is investigated using the scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The electrocatalytic properties for the HER is evaluated based on the cathodic polarization, electrochemical impedance, cyclic voltammetry and chronopotentiometry methods. The obtained results prove the superior catalytic activity for the HER of Ni–Mo/WC composites to Ni–Mo alloy. The catalytic activity of Ni–Mo/WC electrodes is determined by the presence of WC nanoparticles and Mo content in the metallic matrix. The best electrocatalytic properties are identified for Ni–Mo/WC composite with the highest Mo content and the most oxidized surface among the studied coatings. The impedance results reveal that the observed improvement in the catalytic activity is the consequence of high real surface area and high intrinsic catalytic activity of the composite.     

Stabilization of the platinum–ruthenium electrocatalyst against the dissolution of ruthenium with the incorporation of gold

The dissolution of Ru from the PtRu electrocatalyst has been identified as one of the most critical factors in degrading the performance of polymer electrolyte membrane fuel cells (PEMFC). In this work, we prepared an Au-modified PtRu catalyst (Au/PtRu) and found that the incorporation of Au could significantly stabilize the PtRu electrocatalyst against the dissolution of Ru. The X-ray photoelectron spectroscopy (XPS) characterization of the Au/PtRu catalysts revealed that the incorporation of Au increased the oxidation potential of Ru, which is the mechanism that leads to a reduction in the dissolution of Ru from the alloyed catalyst. The XPS characterization of the cathode catalyst also showed that with the PtRu as the anode catalyst Ru appeared at the cathode, but the crossover of Ru could be reduced when the anode catalyst was changed to Au/PtRu.     

Effect of chemisorbed CO on MoOx–Pt/C electrode on the kinetics of hydrogen oxidation reaction

The influence of poisoning of MoO_x–Pt catalyst by CO on the kinetics of H₂ oxidation reaction (HOR) at MoO_x–Pt electrode in 0.5 mol dm⁻³ HClO₄ saturated with H₂ containing 100 ppm CO, was examined on rotating disc electrode (RDE) at 25 °C. MoO_x–Pt nano-catalyst prepared by the polyole method combined with MoO_x post-deposition was supported on commercial carbon black, Vulcan XC-72. The MoO_x–Pt/C catalyst was characterized by TEM technique. The catalyst composition is very similar to the nominal one and post-deposited MoO_x species block only a small fraction of the active Pt particle surface area. MoO_x deposition on the carbon support can be ruled out from the EDAX results and from the low mobility of these oxides under used conditions. Based on Tafel–Heyrovsky–Volmer mechanism the corresponding kinetic equations from a dual-pathway model were derived to describe oxidation current–potential behavior on RDE over entire potential range, at various CO coverages. The polarization RDE curves were fitted with derived polarization equations according to the proposed model. The fitting showed that the HOR proceeded most likely via the Tafel–Volmer (TV) pathway. A very high electrocatalytic activity observed at MoO_x–Pt catalyst for the hydrogen oxidation reaction in the presence of 100 ppm CO is achieved through chemical surface reaction of adsorbed CO with Mo surface oxides.     

Influence of iridium content on the performance and stability of Pd–Ir/C catalysts for the decomposition of hydrogen iodide in the iodine–sulfur cycle

In this paper, a series of bimetallic palladium–iridium catalysts supported on active carbon (Pd–Ir/C) were prepared by the impregnation-reduction method. Effects of the composition on the performance and stability of bimetallic catalysts in the decomposition of HI were investigated. X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) surface area were employed to characterize their structure, morphology and surface area, respectively. The results of activity tests indicated that all the bimetallic Pd–Ir catalysts were more active than the monometallic 5% Pd/C and 5% Ir/C catalysts at both 400 °C and 500 °C. Among Pd, Ir and binary Pd–Ir catalysts, the 4% Pd–1% Ir/C was the most active for HI catalytic decomposition at 400 °C. Due to the low cost, high activity and good stability, the carbon supported bimetallic Pd–Ir catalysts are more potential candidates to replace Pt/C for HI decomposition in the IS thermochemical cycle.     

Effects of the Secondary Air Excess Ratio on the Self-Preheating Combustion Characteristics and NOx,Emission of Semi-Coke

The effects of the secondary air excess ratio(λ₂) on the self-preheating combustion characteristics and NO_x emission of semi-coke have been experimentally studied on a bench-scale test rig.Flameless combustion of the high-temperature preheated fuel(coal gas & coal char) has been achieved in all experimental cases.Through fire-observation windows,the combustion zone was transparent and no flame fronts were seen.Additionally,different λ₂ in this study were basi...     

The PCDD/PCDF Dioxin Releases in the Climate of Environment of Jordan in the Period （2000-2008）

Many environment problems of the full using of several categories of processing include mining, heat generators, direct combustion of forest fires, cement production, power plant, transport, medical waste. Dioxin/furan releases from these categories are one of these environment problems. Possible lines of reducing the PCDD/ PCDF （Polychlorinated dibenzo-para-dioxins/Polychlorinated dibenzofurans） releases from these categories are eluci- dated. The contribution of this paper is present the identification and estimation of the latest figure of dioxin/furan releases in the climate of environment of Jordan in the period 2000-2008 from the following categories （cement, aluminum, ceramic, medical waste, power plant, land fill, ferrous and non- ferrous metals, uncontrolled combustion process （biomass burning, waste burning, accidental fires in house, transport）. These finding shows the sign of growth of estimated PCDD/PCDF releases from categories which did not calculated and followed after 2003. The result shows the highest PCDD/PCDF release from landfill fires （62.75 g TEQ/year）, medical waste （8.8264 g TEQ/year）, and transport （3.0145 g TEQ/year）. Jordan seeks by next years, a reduction in total releases of dioxins and furans from sources resulting from human activity. This challenge will apply to the aggregate of releases to the air nationwide and of releases to the water within the Jordan area. Jordan should conduct air monitoring for dioxin in order to track fluctuations in atmospheric deposition levels.     

Fabrication and evaluation of the electrochemical performance of the anode-supported solid oxide fuel cell with the composite cathode of La0.8Sr0.2MnO3−δ-Gadolinia-doped ceria oxide/La0.8Sr0.2MnO3−δ

The anode-supported single cell was constructed with porous Ni-Yittria-stabilized zirconia (YSZ) as the anode substrate, an airtight YSZ as the electrolyte, and a screen-printed La_0.8Sr_0.2MnO_3−δ (LSM)-Gadolinia-doped ceria (GDC)/LSM double-layer cathode. The SEM results show that the YSZ thin film is highly integrated, fully dense with a thickness of 13 μm, and exhibits excellent compatibility between cathode and electrolyte layers. The effects of feed rates of the reactants, temperature, and contact pressure between the current collector and the unit cell were systematically investigated. The results are based on the assumption that the anode contribution to the polarization resistance is negligible. Our analysis showed that the electrochemical reaction is limited by mass transfer control when the airflow rate is decreased to 500 ml min⁻¹. The maximum power density is 204.6 mW cm⁻² at 800 °C with H₂ and air at flow rates of 800 and 2000 ml min⁻¹, respectively. According to the AC-impedance data, the resistances of charge transfer at the electrode/electrolyte interface are 3.79 and 1.90 Ω cm². The resistances of oxygen-reduction processes are 3.63 and 1.01 Ω cm² at 700 and 800 °C, respectively. The results from the sensitivity analysis of the variation of contact pressure between current collectors and membrane electrode assembly (MEA) show that the influence is enhanced at the regions of the high current density.     

Review of the Debate and the Development of Thrust Vectoring Technology

InMemoryofafriend,Dr.W.HerbstofMBB,Germany,theso-calledfatheroftheX-31experimentalthrustvectoringfighter,wholosthislifeafewyearsagowhilepilotinghisprivateairplane.BertrandRussell'"Menarebornignorant,notstupid-theyaremadestupidbyeducation."AdmiralHymanRickoverf"Thebestengineersarethosewho,inadditiontotechnicalex-pertise,havehadgoodtrainingintheliberalartsandunderstandtheworldaroundthem."ANoLD-NEWEURoPEANDEBArEONTHRUSTVECToRING"talkofthrnstvectoringi8adistrnction,and..thereisn…     

Influence of the substitution of La for Mg on the microstructure and hydrogen storage characteristics of Mg20−xLaxNi10 (x = 0–6) alloys

In order to enhance the glass forming ability of the Mg₂Ni-type hydrogen storage alloy, the Mg in the alloy was partially substituted by La. The alloys Mg_20−xLa_xNi₁₀ (x = 0, 2, 4, 6) were prepared by casting and rapid quenching. The structures and morphologies of the as-cast and the quenched alloys were studied by XRD, SEM and HRTEM. It was found that no amorphous phase was formed in the as-quenched La-free alloy. But the as-quenched alloys containing La held a major amorphous phase, confirming that the substitution of La for Mg significantly enhances the glass forming ability of the alloys. When La content x ≤ 2, the major phase in the as-cast alloys is Mg₂Ni phase, but with the further increase of La content, the major phase of the as-cast alloys changes into (La,Mg)Ni₃ + LaMg₃ phase. Thermal stability of the as-quenched alloys was studied by DSC, showing that La content engenders a negligible influence on the crystallization temperature of the amorphous phase. The hydrogen absorption and desorption kinetics of the as-cast and the quenched alloys were measured by an automatically controlled Sieverts apparatus. The results showed that the hydrogen absorption and desorption capacities and kinetics of the as-cast alloys clearly rise with increasing La content. For La content x = 2, the as-quenched alloy displays an optimal hydrogen desorption kinetics at 200 °C. The electrochemical measurement showed that the discharge capacities of the as-cast alloys rose with the increase of La content, but those of the as-quenched alloys obtained the maximum values with the variation of La content. The cycle stability of the as-cast and the quenched alloys significantly improved with increasing La content.     

An experimental and kinetic modeling study of the autoignition of α-methylnaphthalene/air and α-methylnaphthalene/n-decane/air mixtures at elevated pressures

The autoignition of α-methylnaphthalene (AMN), the bicyclic aromatic reference compound for the cetane number (CN), and AMN/n-decane blends, potential diesel surrogate mixtures, was studied at elevated pressures for fuel/air mixtures in a heated high-pressure shock tube. Additionally, a comprehensive kinetic mechanism was developed to describe the oxidation of AMN and AMN/n-decane blends. Ignition delay times were measured in reflected shock experiments for Φ = 0.5, 1.0, and 1.5 AMN/air mixtures (CN = 0) for 1032-1445 K and 8-45 bar and for Φ = 1.0 30%-molar AMN/70%-molar n-decane/air (CN = 58) and 70%-molar AMN/30%-molar n-decane/air mixtures (CN = 28) for 848-1349 K and 14-62 bar. Kinetic simulations, based on the comprehensive AMN/n-decane mechanism, are in good agreement with measured ignition times, illustrating the emerging capability of comprehensive mechanisms for describing high molecular weight transportation fuels. Sensitivity and reaction flux analysis indicate the importance of reactions involving resonance stabilized phenylbenzyl radicals, the formation of which by H-atom abstractions with OH radicals has an important inhibiting effect on ignition.     

Effect of ionic conductivity of a PVC–LiClO4 based solid polymeric electrolyte on the performance of solar cells of ITO/TiO2/PVC–LiClO4/graphite

This paper reports the effect of ionic conductivity of the solid polymeric electrolyte of polyvinylchloride–lithium perchlorate (PVC–LiClO₄) on the performance of a solar cell of ITO/TiO₂/PVC–LiClO₄/graphite. Titanium dioxide films have been used as a photoelectrochemical solar cells. The films were deposited onto a ITO-coated glass substrate by a screen printing technique. The electrolytes were prepared by solution casting. The ionic conductivity of the electrolytes was obtained with an impedance spectroscopy technique. ITO and graphite films were chosen as the front and counter electrode of the device, respectively. The graphite films were deposited onto a glass substrate by the electron-beam evaporation technique. The short-circuit current density and open-circuit voltage of the device were found to increase with increasing ionic conductivity of solid polymeric electrolyte of PVC–LiClO_4. The highest short-circuit current density and open-circuit voltage were 0.94 μA cm⁻² and 186 mV, respectively. The conversion efficiency was low.