Investigation of hydrogen production from boron compounds for pem fuel cells

This paper presents a comprehensive study of hydrogen production from sodium borohydride (NaBH₄), which is synthesized from sodium tetraborate (Na₂B₄O₇) decomposition, for proton exchange membrane (PEM) fuel cells. For this purpose, Na₂B₄O₇ decomposition reaction at 450–500 °C under hydrogen atmosphere and NaBH₄ decomposition reaction at 25–40 °C under atmospheric pressure are selected as a common temperature range in practice, and the inlet molar quantities of Na₂B₄O₇ are chosen from 1 to 6 mol with 0.5 mol interval as well. In order to form NaBH₄ solution with 7.5 wt.% NaBH₄, 1 wt.% NaOH, 91.5 wt.% H₂O, the molar quantities of NaBH₄ are determined. For a PEM fuel cell operation, the required hydrogen production rates are estimated depending on 60, 65, 70 and 75 g of catalyst used in the NaBH₄ solution at 25, 32.5 and 40 °C, respectively. It is concluded that the highest rate of hydrogen production per unit area from NaBH₄ solution at 40 °C is found to be 3.834 × 10⁻⁵ g H₂ s⁻¹ cm⁻² for 75 g catalyst. Utilizing 80% of this hydrogen production, the maximum amounts of power generation from a PEM fuel cell per unit area at 80 °C under 5 atm are estimated as 1.121 W cm⁻² for 0.016 cm by utilizing hydrogen from 75 g catalyst assisted NaBH₄ solution at 40 °C.     

Hydrogen generation from solid state NaBH4 by using FeCl3 catalyst for portable proton exchange membrane fuel cell applications

Being a boron-based compound, sodium borohydride, NaBH₄, is a convenient hydrogen storage material for applications like unmanned air vehicles. There are several concerns behind commercialization of hydrogen gas generator by NaBH₄ hydrolysis systems. This study aims to contribute to the solution of the problems of NaBH₄ hydrolysis system in three main ways. First, the usage of solid state NaBH₄ enables to increase the durability and the gravimetric H₂ storage capacity of the system in order to meet US DOE targets. Second, solid NaBH₄ usage decreases the system's weight since it does not require a separate fuel storage tank, which is very important for portable, on demand applications. Finally, the system's cost is decreased by using an accessible and effective non-precious catalyst such as ferric chloride, FeCl₃. The maximum hydrogen generation rate obtained was 2.6 L/min and the yield was 2 L H₂/g NaBH₄ with an efficiency of 76% at its most promising condition. Moreover, the novel solid NaBH₄ hydrogen gas generator developed in the present work was integrated into a proton exchange membrane fuel cell and tested at the optimum operating conditions.     

Creep behavior of Ni-12 wt.% Al anodes for molten carbonate fuel cells

Ni-12 wt.% Al anodes are fabricated for use in molten carbon fuel cells by tape casting and sintering. Sintering is performed in three steps, first at 1200 °C for 10 min in argon, then at 700 °C for 2.5 h in a partial oxidation atmosphere (P_H2/P_H2O=10⁻²), and finally at 950 °C for 5 min, 30 min or 1.5 h in hydrogen. Three anodes with different phases or microstructures are produced at different reduction times. One anode contains three phases, namely Ni–Al solid solution, Ni₃Al, and Al₂O₃. The amount of Al₂O₃ is extremely small at 5 min. A second anode also contains the three phases with the amount of Al₂O₃ comparable with that of Ni₃Al at 30 min. Third anode contains two phases, i.e. Ni–Al solid solution and Al₂O₃ formed at 1.5 h. The creep strains measured for the three anodes after a 100-h creep test are practically the same with an average value of 0.85%.     

Production of NaBH4 and hydrogen release with catalyst

The purpose of this study was to investigate the production of NaBH₄ as hydrogen storage material and testing its hydrogen storage capacity in presence of catalyst. Synthesis of NaBH₄ was investigated with NaH and trimethyl borate which was also produced in previous studies. Different reaction temperatures, times and reactant ratios constitute the three parameters of the production process. The best combination determined by FT-IR, XRF and XRD analyses, was found to be 1.413 (mol/mol) TMB over NaH at 250 °C for 90 min. In order to increase the NaBH₄ purity ethylene diamine was used as solvent at 75 °C. After 4 extraction and crystallization processes 85.17% NaBH₄ purity was obtained. Moreover, hydrogen content of the product NaBH₄ was measured in a system with different catalysts since catalyst efficiency is important in decreasing the water dependence of dehydrogenation. CoCl₂ catalyst proved best by taking out more hydrogen, both from the NaBH₄ structure and from water.     

Operation of ceria-electrolyte solid oxide fuel cells on iso-octane–air fuel mixtures

Reduced-temperature solid oxide fuel cells (SOFCs) – with thin Ce_0.85Sm_0.15O_1.925 (SDC) electrolytes, thick Ni–SDC anode supports, and composite cathodes containing La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) and SDC – were fabricated and tested with iso-octane/air fuel mixtures. An additional supported catalyst layer, placed between the fuel stream and the anode, was needed to obtain a stable output power density (e.g. 0.6 W cm⁻² at 590 °C) without anode coking. The Ru-CeO₂ catalyst produced CO₂ and H₂ at temperatures <350 °C, while H₂ and CO became predominant above 500 °C. Power densities were substantially less than for the same cells with H₂ fuel (e.g. 1.0 W cm⁻² at 600 °C), due to the dilute (≈20%) hydrogen in the fuel mixture produced by iso-octane partial oxidation. Electrochemical impedance analysis showed a main arc that represented ≈60% of the total resistance, and that increased substantially upon switching from hydrogen to iso-octane/air.     

A 75-kW methanol reforming fuel cell system

A 75-kW methanol reforming fuel cell system, which consists of a fuel cell system and a methanol auto-thermal reforming fuel processor has been developed at Dalian Institute of Chemical Physics, Chinese Academy of Sciences (CAS). The core of the fuel cell system is a group of CO tolerant PEMFC stacks with a double layer composite structured anode. The fuel cell stacks show good CO tolerance even though 140 ppm CO was present in the reformate stream during transients. The auto-thermal reforming (ATR) fuel cell processor could adiabatically produce a suitable reformate without external energy consumption. The output of hydrogen-rich reformate was approximately 120 N m³ h⁻¹ with a H₂ content near 53% and the CO concentrations generally were under 30 ppm. The fuel cell system was integrated with the methanol reforming fuel processor and the peak power output of the fuel cell system exceeded 75 kW in testing. The hydrogen utilization approached 70% in the fuel cell system.     

A 28-W portable direct borohydride–hydrogen peroxide fuel-cell stack

A 28-W direct borohydride–hydrogen peroxide fuel-cell stack operating at 25 °C is reported for contemporary portable applications. The fuel cell operates with the peak power-density of ca. 50 mW cm⁻² at 1 V. This performance is superior to the anticipated power-density of 9 mW cm⁻² for a methanol–hydrogen peroxide fuel cell. Taking the fuel efficiency of the sodium borohydride–hydrogen peroxide fuel cell as 24.5%, its specific energy is ca. 2 kWh kg⁻¹. High power-densities can be achieved in the sodium borohydride system because of its ability to provide a high concentration of reactants to the fuel cell.     

Chemical reduction method for industrial application of undoped polypyrrole electrodes in lithium-ion batteries

This work describes a new method of chemical reduction of p-doped polypyrrole (Ppy) to make a graphite/Ppy lithium-ion battery. Several reducing agents are analysed (sodium hydrosulfite (Na₂S₂O₄), sodium hydrogensulfite (Na₂S₂O₅), hydroxymethanesulfinic acid monosodium salt (HOCH₂SOONa), sodium borohydride (NaBH₄), formamidinesulfinic acid (H₂NCNHSO₂H), stannous chloride (SnCl₂) and hydrazine (N₂H₄)), obtaining the best results when reducing a Ppy electrode with sodium borohydride (NaBH₄): at least 85% of the polymer electrode can be reduced without significant degradation. To verify the feasibility of the reduction method two lithium-ion batteries with a Ppy cathode have been assembled using different ways (4.5 cm × 1.9 cm electrodes having similar active electrode material (mg cm⁻²) values and thicknesses to commercial inorganic oxide electrodes). In one of them the doped Ppy electrode is previously electrochemically reduced, applying consecutive potentials steps before the cell assembling; it would be accurate and easy at laboratory scale, but from an industrial point of view it is complicated and not viable. In the second battery the doped Ppy electrode is chemically reduced resulting in a similar charge–discharge characteristic to the electrochemically reduced one. Therefore, the chemical reduction method can be a step forward for using Ppy as cathode in lithium-ion batteries at industry level.     

Data results and operational experience with a solar hydrogen system

A solar hydrogen system is presented able to provide uninterrupted 200 W_e power to an isolated application. It is composed of a photovoltaic generator, a battery set, an electrolyser, a metal-hydride system for hydrogen storage and a fuel cell. Batteries are charged with the photovoltaic array and the fuel cell, and discharged with the electrolyser and the application load. The fuel cell switches on when the state of charge of the batteries is low, until they are recovered to a predetermined level. The electrolyser produces H₂ at 30 bar, enough to feed directly the metal hydrides, avoiding pressurization steps. Metal hydrides work under pressure control in the temperature range 0–40 °C. Kinetics of absorption–desorption of hydrogen is observed as an important limiting aspect for this kind of storage. The system is able to convert about 6–7% of total solar energy irradiated in 1 year. Results and evaluation after 1-year operation are shown. Energy management is found to be a critical issue to improve the behavior of the system.     

Negative pressure dependence of mass burning rates of H2/CO/O2/diluent flames at low flame temperatures

Experimental measurements of burning rates, analysis of the key reactions and kinetic pathways, and modeling studies were performed for H₂/CO/O₂/diluent flames spanning a wide range of conditions: equivalence ratios from 0.85 to 2.5, flame temperatures from 1500 to 1800 K, pressures from 1 to 25 atm, CO fuel fractions from 0 to 0.9, and dilution concentrations of He up to 0.8, Ar up to 0.6, and CO₂ up to 0.4. The experimental data show negative pressure dependence of burning rate at high pressure, low flame temperature conditions for all equivalence ratios and CO fractions as high as 0.5. Dilution with CO₂ was observed to strengthen the pressure and temperature dependence compared to Ar-diluted flames of the same flame temperature. Simulations were performed to extend the experimentally studied conditions to conditions typical of gas turbine combustion in Integrated Gasification Combined Cycle processes, including preheated mixtures and other diluents such as N₂ and H₂O.Substantial differences are observed between literature model predictions and the experimental data as well as among model predictions themselves – up to a factor of three at high pressures. The present findings suggest the need for several rate constant modifications of reactions in the current hydrogen models and raise questions about the sufficiency of the set of hydrogen reactions in most recent hydrogen models to predict high pressure flame conditions relevant to controlling NO_x emissions in gas turbine combustion. For example, the reaction O + OH + M = HO₂ + M is not included in most hydrogen models but is demonstrated here to significantly impact predictions of lean high pressure flames using rates within its uncertainty limits. Further studies are required to reduce uncertainties in third body collision efficiencies for and fall-off behavior of H + O₂(+M) = HO₂(+M) in both pure and mixed bath gases, in rate constants for HO₂ reactions with other radical species at higher temperatures, and in rate constants for reactions such as O + OH + M that become important under the present conditions in order to properly characterize the kinetics and predict global behavior of high-pressure H₂ or H₂/CO flames.     

Biodiesel production by esterification of palm fatty acid distillate

Production of fatty acid methyl ester (FAME) from palm fatty acid distillate (PFAD) having high free fatty acids (FFA) was investigated in this work. Batch esterifications of PFAD were carried out to study the influence of: including reaction temperatures of 70–100 °C, molar ratios of methanol to PFAD of 0.4:1–12:1, quantity of catalysts of 0–5.502% (wt of sulfuric acid/wt of PFAD) and reaction times of 15–240 min. The optimum condition for the continuous esterification process (CSTR) was molar ratio of methanol to PFAD at 8:1 with 1.834 wt% of H₂SO₄ at 70 °C under its own pressure with a retention time of 60 min. The amount of FFA was reduced from 93 wt% to less than 2 wt% at the end of the esterification process. The FAME was purified by neutralization with 3 M sodium hydroxide in water solution at a reaction temperature of 80 °C for 15 min followed by transesterification process with 0.396 M sodium hydroxide in methanol solution at a reaction temperature of 65 °C for 15 min. The final FAME product met with the Thai biodiesel quality standard, and ASTM D6751-02.     

Fuel cell buses in the Stockholm CUTE project—First experiences from a climate perspective

This paper aims to share the first experiences and results from the operation of fuel cell buses in Stockholm within the Clean Urban Transport for Europe (CUTE) project. The project encompasses implementation and evaluation of both a hydrogen fuel infrastructure and fuel cell vehicles in nine participating European cities. In total, 27 fuel cell buses, 3 in each city, are in revenue service for a period of 2 years.The availability of the fuel cell buses has been better than expected, about 85% and initially high fuel consumption has been reduced to approximately 2.2 kg H₂/10 km corresponding to 7.5 l diesel equivalents/10 km. Although no major breakdowns have occurred so far, a few cold climate-related issues did arise during the winter months in Stockholm.     

Solid oxide fuel cells operated by internal partial oxidation reforming of iso-octane

Two types of solid oxide fuel cells (SOFCs), with thin Ce_0.85Sm_0.15O_1.925 (SDC) or 8 mol% Y₂O₃-stabilized ZrO₂ (YSZ) electrolytes, were fabricated and tested with iso-octane/air fuel mixtures. An additional Ru–CeO₂ catalyst layer, placed between the fuel stream and the anode, was needed to obtain a stable output power density without anode coking. Thermodynamic analysis and catalysis experiments showed that H₂ and CO were primary reaction products at ≈750 °C, but that these decreased and H₂O and CO₂ increased as the operating temperature dropped below ≈600 °C. Power densities for YSZ cells were 0.7 W cm⁻² at 0.7 V and 790 °C, and for SDC cells were 0.6 W cm⁻² at 0.6 V and 590 °C. Limiting current behavior was observed due to the relatively low (≈20%) H₂ content in the reformed fuel.     

Performance of a poly(2,5-benzimidazole) membrane based high temperature PEM fuel cell in the presence of carbon monoxide

The performance of a poly(2,5-benzimidazole) (ABPBI) membrane based high temperature PEM fuel cell in presence of carbon monoxide, at various temperatures is reported here. The ABPBI was synthesized by polymerization of 3,4-diaminobenzoic acid in a polymerization medium containing methanesulfonic acid (CH₃SO₃H) and phosphorous pentoxide (P₂O₅). The ABPBI membranes were characterized by fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). A maximum conductivity of 0.026 S cm⁻¹ at 180 °C was obtained for the membrane doped with 1.2 molecules of phosphoric acid (H₃PO₄) per polymer repeat unit. Fuel cell performance was evaluated using dry hydrogen/oxygen gases and was comparable with that reported in the literature. Performance of a single cell at different temperatures was studied with 0.48 and 1.0 vol.% of CO in the hydrogen fuel. The studies lead to the conclusion that CO poisoning is not a serious problem above 170 °C. Performance of the fuel cell operating at 210 °C is not at all affected by 1.0 vol.% of CO in the hydrogen feed.     

Effects of coal syngas and H2S on the performance of solid oxide fuel cells: Single-cell tests

The performance of single-cell planar solid oxide fuel cells using coal syngas, with and without hydrogen sulfide (H₂S), was studied. A state-of-the-art gas delivery system, data acquisition system, and test stand were designed and assembled for experimentation. All cells were tested at 850 °C with a constant current load of 14.3 A (current density of 0.20 A cm⁻²). The results from using syngas with no H₂S indicated no degradation after 290 h of operation. After immediately injecting CO (and water) in the H₂–N₂ mixture, there was a slight tendency of improving performance (power) and then the behavior remained steady. On the other hand, results for the test with syngas in the presence of H₂S (200–240 ppm) indicated good performance over 570 h (650 h total operation time) with 10–12.5% degradation. The results suggest these cells can be used for extended periods of time for syngas applications, and in the presence of H₂S the cells show no major degradation.     

Development of a miniaturized polymer electrolyte membrane fuel cell with silicon separators

The fabrication process and electrochemical characterization of a miniaturized PEM fuel cell with silicon separators were investigated. Silicon separators were fabricated with silicon fabrication technologies such as by photolithography, anisotropic wet etching, anodic bonding and physical vapor deposition (PVD). A 400 μm × 230 μm flow channel was made with KOH wet etching on the front side of a silicon separator, and then a 550 nm gold current collector and 350 nm TiN_x thin film heater were respectively formed on the front side and the opposite side by PVD. Two separators were assembled with the membrane electrode assembly (MEA) having a 4 cm² active area for the single cell. With pure hydrogen and oxygen under atmospheric pressure without humidification, the performance of the single fuel cell was measured. A single cell operation led to generation of 203 mW cm⁻² at 0.6 V at room temperature, which corresponded to 360 mW cm⁻³ in terms of volumetric fuel cell power density, with 20 ccm of gas flow rate of hydrogen and oxygen at the inlet.     

Effects of dilution with carbon dioxide on the laminar burning velocity and flame stability of H2–CO mixtures at atmospheric condition

The objective of this investigation was to study the effect of dilution with CO₂ on the laminar burning velocity and flame stability of syngas fuel (50% H₂–50% CO by volume). Constant pressure spherically expanding flames generated in a 40 l chamber were used for determining unstretched burning velocity. Experimental and numerical studies were carried out at 0.1 MPa, 302 ± 3 K and ? = 0.6–3.0 using fuel-diluent and mixture-diluent approaches. For H₂–CO–CO₂–O₂–N₂ mixtures, the peak burning velocity shifts from ? = 2.0 for 0% CO₂ in fuel to ? = 1.6 for 30% CO₂ in fuel. For H₂–CO–O₂–CO₂ mixtures, the peak burning velocity occurred at ? = 1.0 unaffected by proportion of CO₂ in the mixture. If the mole fraction of combustibles in H₂–CO–O₂–CO₂ mixtures is less than 32%, then such mixtures are supporting unstable flames with respect to preferential diffusion. The analysis of measured unstretched laminar burning velocities of H₂–CO–O₂–CO₂ and H₂–CO–O₂–N₂ mixtures suggested that CO₂ has a stronger inhibiting effect on the laminar burning velocity than nitrogen. The enhanced dilution effect of CO₂ could be due to the active participation of CO₂ in the chemical reactions through the following intermediate reaction CO + OH ? CO₂ + H.     

Supported CoCl2 catalyst for NaBH4 dehydrogenation

In this paper, economically favorable, supported CoCl₂ catalysts were produced for NaBH₄ dehydrogenation. Among the used supports, diatomite and γ-Al₂O₃ supports show great stability with CoCl₂ and do not break up during experiments some of which lasts 3000 min. Slow and continuous hydrogen release throughout all of the experiments is observed. Furthermore, prepared catalyst could be used for 250 h uninterruptedly. XRF and Atomic Absorption Spectrometer (AAS) analysis prove that CoCl₂ could be permanently joined and distributed homogeneously on the support surface. In addition, kinetic investigations of the dehydrogenation reaction fit zero order kinetic for low temperatures while it obeys the first order at high temperature. Computation of activation energy results 132 kJ/mol for low and 78 kJ/mol for high temperature regions.     

Thermodynamic evaluation of methanol steam reforming for hydrogen production

Thermodynamic equilibrium of methanol steam reforming (MeOH SR) was studied by Gibbs free minimization for hydrogen production as a function of steam-to-carbon ratio (S/C = 0–10), reforming temperature (25–1000 °C), pressure (0.5–3 atm), and product species. The chemical species considered were methanol, water, hydrogen, carbon dioxide, carbon monoxide, carbon (graphite), methane, ethane, propane, i-butane, n-butane, ethanol, propanol, i-butanol, n-butanol, and dimethyl ether (DME). Coke-formed and coke-free regions were also determined as a function of S/C ratio.Based upon a compound basis set MeOH, CO₂, CO, H₂ and H₂O, complete conversion of MeOH was attained at S/C = 1 when the temperature was higher than 200 °C at atmospheric pressure. The concentration and yield of hydrogen could be achieved at almost 75% on a dry basis and 100%, respectively. From the reforming efficiency, the operating condition was optimized for the temperature range of 100–225 °C, S/C range of 1.5–3, and pressure at 1 atm. The calculation indicated that the reforming condition required from sufficient CO concentration (<10 ppm) for polymer electrolyte fuel cell application is too severe for the existing catalysts (T_r = 50 °C and S/C = 4–5). Only methane and coke thermodynamically coexist with H₂O, H₂, CO, and CO₂, while C₂H₆, C₃H₈, i-C₄H₁₀, n-C₄H₁₀, CH₃OH, C₂H₅OH, C₃H₇OH, i-C₄H₉OH, n-C₄H₉OH, and C₂H₆O were suppressed at essentially zero. The temperatures for coke-free region decreased with increase in S/C ratios. The impact of pressure was negligible upon the complete conversion of MeOH.     

Performance of a solid oxide fuel cell utilizing hydrogen sulfide as fuel

The electrochemical performance of a hydrogen sulfide solid oxide fuel cell having the configuration H₂S, Pt/(ZrO₂)_0.92(Y₂O₃)_0.08/Pt, air has been examined at atmospheric pressure and 750–800°C, using both pure and 5% H₂S anode feed streams. The performance of the cell is higher when using diluted H₂S feed compared with pure H₂S feed: current densities up to 100 mA cm⁻² and power densities up to 15.4 mW cm⁻² have been achieved using diluted H₂S gas (5%) at 800°C. However, the platinum anode degrades over time in H₂S stream due to the formation of PtS. Electrochemical oxidation of H₂S on the Pt anode significantly accelerated its degradation. Polarization and impedance spectroscopy measurements show that at low current density (i) electrochemical reaction is the major cause of polarization in the fuel cell. Ohmic loss due to the resistance of the electrolyte material and the electrical connecting wire is a major part of cell polarization at high i.