Externally reformed solid oxide fuel cell–micro-gas turbine (SOFC–MGT) hybrid systems fueled by methanol and di-methyl-ether (DME)

Solid oxide fuel cell–micro-gas turbine (SOFC–MGT) hybrid power plants integrate a solid oxide fuel cell and a micro-gas turbine and can achieve efficiencies of over 60% even for small power outputs (200–500 kW). The SOFC–MGT systems currently developed are fueled with natural gas, which is reformed inside the same stack, but the use of alternative fuels can be an interesting option. In particular, as the reforming temperature of methanol and di-methyl-ether (DME) (200–350 °C) is significantly lower than that of natural gas (700–900 °C), the reformer can be sited outside the stack. External reforming in SOFC–MGT plants fueled by methanol and DME enhances efficiency due to improved exhaust heat recovery and higher voltage produced by the greater hydrogen partial pressure at the anode inlet. The study carried out in this paper shows that the main operating parameters of the fuel reforming section (temperature and steam-to-carbon ratio (SCR)) must be carefully chosen to optimise the hybrid plant performance. For the stoichiometric SCR values, the optimum reforming temperature for the methanol fueled hybrid plant is approximately 240 °C, giving efficiencies of about 67–68% with a SOFC temperature of 900 °C (the efficiency is about 72–73% at 1000 °C). Similarly, for DME the optimum reforming temperature is approximately 280 °C with efficiencies of 65% at 900 °C (69% at 1000 °C). Higher SCRs impair stack performance. As too small SCRs can lead to carbon formation, practical SCR values are around one for methanol and 1.5–2 for DME.     

Pd–Ag hydrogen content and electrical resistivity: Temperature and pressure effect

A Pd–Ag (silver 21 wt.%) thin sheet has been tested in order to measure its electrical resistivity by means of electrochemical impedance spectroscopy under different hydrogenation conditions in the temperature range 25–350 °C. The metal sheet has been assembled with the electrical contacts in a gas tight module where pure hydrogen has been fed at a pressure of 100 and 200 kPa.     

Electrical conductivity and P-wave velocity in rock samples from high-temperature Icelandic geothermal fields

Measurements of electrical conductivity and P-wave velocity of seven rock samples were made in the laboratory under inferred in situ conditions. The samples were collected from smectite and chlorite alteration zones in boreholes from the Krafla and Hengill, Iceland, geothermal areas. The measurements were done in the 25–250 °C range, with pore pressure and confining pressure equal to inferred in situ hydrostatic and lithostatic pressures, respectively. Conductivity increases linearly with temperature over the 30–170 °C range; that rise is considerably smaller above 170 °C. Time-dependent effects on conductivity occur above approximately 100 °C. These effects may be related to ion exchange between the clay minerals or the Stern layer, and the pore fluid. The temperature coefficient of conductivity is found to be considerably higher than attributed to pore fluid conduction alone, indicating interface conduction in an electrical double layer on the mineral-water interface in the pores. The results also show that there is no distinction in electrical conduction mechanism in the smectite and chlorite alteration zones; both are dominated by interface conductivity under in situ conditions. The sharp decrease in conductivity at the top of the chlorite alteration zone, commonly observed in resistivity surveys in high-temperature geothermal systems, is most likely due to the lower cation exchange capacity of chlorite compared to that of smectite.     

Study on Ni–Fe–C cathode for hydrogen evolution from seawater electrolysis

Hydrogen evolution reaction in 3.5 wt% NaCl (simulated seawater) was investigated using Ni–Fe–C cathode, prepared by cathode electrodeposits method on the matrix of A3 steel. The as-prepared Ni–Fe–C cathode coating materials has reached nanometer grade, what is more, the limit of average grain size was about 4.3 nm. As decreasing of the average coating grain sizes, hydrogen evolution overpotential was not decreasing linearly. There was a boundary average coating grain sizes of about 4.3–6.4 nm. The optimal preparation process of Ni–Fe–C cathode was listed as electroplating current density 200 A/m², temperature 30 °C, pH 1.5 and 60 min. The hydrogen overpotential was only about 65 mV, which was tested in the 3.5 wt% NaCl of 90 °C at pH 12.     

History of geothermal exploration in Indonesia from 1970 to 2000

Reconnaissance surveys undertaken since the 1960s show that more than 200 geothermal prospects with significant active surface manifestations occur throughout Indonesia. Some 70 of these were identified by the mid-1980s as potential high-temperature systems using geochemical criteria of discharged thermal fluids. Between 1970 and 1995, about 40 of these were explored using geological mapping, geochemical and detailed geophysical surveys. Almost half of the surveyed prospects were tested by deep (0.5–3 km) exploratory drilling, which led to the discovery of 15 productive high-temperature reservoirs. Several types of reservoirs were encountered: liquid-dominated, vapour-dominated, and a vapour layer/liquid-saturated substratum type. All three may be modified by upflows (plumes) containing magmatic fluid components (volcanic geothermal systems). Large, concealed outflows are a common feature of liquid-dominated systems in mountainous terrain. All explored prospects are hosted by Quaternary volcanic rocks, associated with arc volcanism, and half occur beneath the slopes of active or dormant stratovolcanoes. By 1995, five fields had been developed by drilling of production wells; three of them supplied steam to plants with a total installed capacity of 305 MW_e. By 2000, with input from foreign investors, the installed capacity had reached 800 MWe in six fields, but geothermal developments had stalled because of the 1997–1998 financial crisis.     

Carbon-supported Ir–V nanoparticle as novel platinum-free anodic catalysts in proton exchange membrane fuel cell

The active, carbon-supported Ir–V nanoparticle catalysts were successfully synthesized using IrCl₃ and NH₄VO₃ as the Ir and V precursors in ethylene glycol refluxing at 120 °C with varying pH values, then further reduction under hydrogen atmosphere at 200 °C. The nanostructured catalysts were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (TEM). These carbon-supported catalysts give a good dispersion of Ir–V/C electrocatalysts with mean particle size of 2–3 nm, thus leading to a marked promotion of hydrogen oxidation reaction. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry techniques (CV) were used to characterize on-line the performance of the proton exchange membrane fuel cell (PEMFC) using several anode catalysts at different pH values. It was found that the pH value for the synthesis of catalysts affects the performance of electrocatalysts significantly, based on the discharge characteristics of the fuel cell. High cell performance on the anode was achieved with a loading of 0.4 mg cm⁻² 40%Ir–10%V/C catalyst synthesized at pH 12, which results in a maximum a power density of 1008 mW cm⁻² at 0.6 V and 70 °C. This is 50% higher performance than that for commercial available Pt/C catalyst. Fuel cell life test at a constant current density of 1000 mA cm⁻² demonstrated an initial stability up to 100 h generating a cell voltage of 0.6 V, which strongly suggests that the novel Ir–V/C nanoparticle catalysts proposed in this work could be promising for PEMFC.     

Alcohol electrooxidation at Pt and Pt–Ru sputtered electrodes under elevated temperature and pressurized conditions

The electrooxidation properties of methanol and 2-propanol, which are both promising candidates for direct alcohol fuel cells (DAFCs), have been studied under elevated temperature and pressurized conditions. Sputter-deposited Pt and Pt–Ru electrodes were well-characterized and utilized for the electrochemical measurement of the alcohol oxidation at 25–100 °C. The Pt electrode prepared at 600 °C had a flat surface, and the Pt–Ru formed an alloy. The electrochemical measurements were carried out in a gas-tight cell under elevated temperature, which accompanies the pressurized condition. This is a representative example of the DAFC rising temperature operation. As a result, at 25 °C, the onset potential of the 2-propanol oxidation is about 400 mV more negative than that of the methanol oxidation, and current density of the 2-propanol oxidation exceeds that of the methanol oxidation. Conversely, at 100 °C, the methanol oxidation current density overcomes that of 2-propanol, and the onset potentials of the two are almost the same. The highest current density for the methanol oxidation is obtained at the Pt:Ru = 50:50 electrode, whereas at the Pt:Ru = 35:65 for the 2-propanol oxidation. A Tafel plot analysis was employed to investigate the reaction mechanism. For the methanol oxidation, the number of electrons transferred during the rate-determining process is estimated to be 1 at 25 °C and 2 at 100 °C. This suggests that the methanol reaction mechanism differs at 25 and 100 °C. In contrast, the rate-determining process of the 2-propanol oxidation at 25 and 100 °C was expected to be 1-electron transfer which accompanies the proton-elimination reaction to produce acetone. Consequently, it is deduced that methanol and 2-propanol have an advantage under the rising temperature and room temperature operation, respectively.     

Two-step sintering ceria-based electrolytes

Yttrium and gadolinium-doped ceria-based electrolytes (20 at% dopant cation) with and without small Ga₂O₃-additions (0.5 mol%) were fired at peak temperatures of 1250 and 1300 °C, or following a two-step sintering profile including one peak temperature and subsequent dwell at 1150 °C, 10 h. All materials were characterized by scanning electron microscopy, X-ray diffraction and impedance spectroscopy in air, in the temperature range 200–800 °C. Average grain sizes in the range 150–250 nm and densifications up to about 94% were found dependent on the sintering profile and presence of Ga. The grain boundary arcs in the impedance spectra increased significantly with Ga-doping, cancelling the apparently positive role of Ga on bulk transport, evidenced mostly in the case of yttrium-doped materials.     

Joint 1D inversion of TEM and MT data and 3D inversion of MT data in the Hengill area,SW Iceland

An extensive study of the resistivity structure of the Hengill area in SW Iceland was carried out by the combined use of TEM and MT soundings. Joint inversion of the collected data can correct for static shifts in the MT data, which can be severe due to large near-surface resistivity contrasts. Joint 1D inversion of 148 TEM/MT sounding pairs and a 3D inversion of a 60 sounding subset of the MT data were performed. The 3D inversion was based on full MT impedance tensors previously corrected for static shift. Both inversion approaches gave qualitatively similar results, and revealed a shallow resistivity layer reflecting conductive alteration minerals at temperatures of 100–240 °C. They also delineated a deep conductor at 3–10 km depth. The reason for this deep-seated high conductivity is not fully understood. The distribution of the deep conductors correlates with a positive residual Bouguer gravity anomaly, and with transform tectonics inferred from seismicity. One model of the Hengill that is consistent with the well temperature data and the deep conductor that does not attenuate S-waves, is a group of hot, solidified, but still ductile magmatic intrusions that are closely associated with the heat source for the geothermal system.     

Application of nickel–lanthanum composite oxide on the steam reforming of ethanol to produce hydrogen

Nickel–lanthanum composite oxides, LaNiO_x, were used for steam reforming of ethanol (SRE). The composite oxides (with 3:1, 1:1, 1:3 M ratios, assigned as 3La–1Ni, 1La–1Ni, and 1La–3Ni, respectively) were prepared by co-precipitation-oxidation (PO) and assisted with ultrasonic irradiation (240 W). Meanwhile, the as-prepared 1La–1Ni sample was further calcined at 300 and 700 °C for 2 h (assigned as C300 and C700). All samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and temperature programmed reduction (TPR). Catalytic activities towards the SRE reaction were tested from 300 to 450 °C in a fixed-bed reactor. The study focused on deriving optimized composition of composites and compared the effect on the reduction pretreatment under 200 °C [assigned with (H)]. The results indicated that the ethanol conversion reached completion around 325 °C for the 1La–1Ni(H) sample while it required 400 °C for the 1La–1Ni sample with a minor CO distribution for both samples under an H₂O/EtOH molar ratio of 13 and 22,000 h⁻¹ GHSV. The yield of hydrogen (YH₂$Y_{{\text{H}}_2}$) approached 5.2 around 375 °C for the 1La–1Ni(H) sample.     

Polymer electrolytes based on sulfonated polysulfone for direct methanol fuel cells

This paper reports the development and characterization of sulfonated polysulfone (SPSf) polymer electrolytes for direct methanol fuel cells. The synthesis of sulfonated polysulfone was performed by a post sulfonation method using trimethyl silyl chlorosulfonate as a mild sulfonating agent. Bare polysulfone membranes were prepared with two different sulfonation levels (60%, SPSf-60 and 70%, SPSf-70), whereas, a composite membrane of SPSf-60 was prepared with 5 wt% silica filler. These membranes were investigated in direct methanol fuel cells (DMFCs) operating at low (30–40 °C) and high temperatures (100–120 °C). DMFC power densities were about 140 mW cm⁻² at 100 °C with the bare SPSf-60 membrane and 180 mW cm⁻² at 120 °C with the SPSf-60-SiO2 composite membrane. The best performance achieved at ambient temperature using a membrane with high degree of sulfonation (70%, SPSf-70) was 20 mW cm⁻² at atmospheric pressure. This makes the polysulfone-based DMFC suitable for application in portable devices.     

ZrO2–SiO2/Nafion composite membrane for polymer electrolyte membrane fuel cells operation at high temperature and low humidity

Recast Nafion^® composite membranes containing ZrO₂–SiO₂ binary oxides with different Zr/Si ratios are investigated for polymer electrolyte membrane fuel cells (PEMFCs) at temperatures above 100 °C. Fine particles of the ZrO₂–SiO₂ binary oxides, same as an inorganic filter, are synthesized from a sodium silicate and a carbonate complex of zirconium by a sol–gel technique. The composite membranes are prepared by blending a 10% (w/w) Nafion^®-water dispersion with the inorganic compound. All composite membranes show higher water uptake than unmodified membranes, and the proton conductivity increases with increasing zirconia content at 80 °C. By contrast, the proton conductivity decreases with zirconia content for the composite membranes containing binary oxides at 120 °C. The composite membranes are tested in a 9-cm² commercial single cell at both 80 °C and 120 °C in humidified H₂/air under different relative humidity (RH) conditions. Composite membrane containing the ZrO₂–SiO₂ binary oxide (Zr/Si = 0.5) give the best performance of 610 mW cm⁻¹ under conditions of 0.6 V, 120 °C, 50% RH and 2 atm.     

New manganese dioxides for lithium batteries

Lithium/manganese dioxide primary batteries use heat treated manganese dioxide (HEMD), a defect pyrolusite structure material as the cathode active material. Ion exchange of the structural protons in electrolytic manganese dioxide (EMD) with lithium before heating results in formation of a lithium containing γ-MnO₂. Increased lithium hydroxide concentration and increased temperature lead to increased lithium levels. At 80 °C with a combination of LiOH and LiBr, almost all of the structural protons in MnO₂ are replaced by lithium resulting in a γ-MnO₂ phase substantially free of protons and containing about 1.8% Li. This highly substituted lithium containing MnO₂ is reduced at between 3.5 and 1.8 V and has a capacity of 250 mAh g⁻¹. There are two reduction processes, one at 3.25 and the other at 2.9 V. TGA studies reveal two processes during heat treatment. Heating the lithium substituted MnO₂ to 350–400 °C results in a partially ordered HEMD-like MnO₂ (LiMD) phase with higher running voltage and superior discharge kinetics. Continued heating of the lithiated manganese dioxide to 450–480 °C under oxygen partial pressure can result in formation of a mixed phase containing both HEMD and a new, ordered MnO₂ phase (OMD). The intimately mixed HEMD/OMD composition has a discharge voltage near 2.9 V with a capacity about 220 mAh g⁻¹. Heating exhaustively lithiated MnO₂ to 350–400 °C results in formation of the partially ordered LiMD MnO₂ phase as with the previous partially lithium substituted MnO₂. Additional heating of the highly lithium substituted MnO₂ to 450–480 °C under oxygen results in formation of the new OMD phase in substantially pure form. Discharge of the new OMD phase shows it has a discharge capacity near 200 mAh g⁻¹ between 3.4 and 2.4 V versus lithium in a single, well-defined discharge process. OMD demonstrated good cycling against Li with no indication of formation of LiMn₂O₄ spinel after 80 deep discharge cycles.     

Conductivity,thermal behavior and microstructure of new composites based on AgI–Ag2O–B2O3 glasses with Al2O3 matrix

A series of Ag⁺-ion conducting composites consisting of glasses of the AgI–Ag₂O–B₂O₃ system and hard Al₂O₃ powder matrix were synthesized by a high-pressure route (pressure 7.7 GPa, temperature 100–200 °C). The composition of the glasses was described by the general formula: xAgI·(100 − x)(0.667Ag₂O·0.333B₂O₃), where x = 40, 50 and 60. Alumina powder (2 μm average grain size) was added to the glass in 50/50 proportions (by volume).     

Performance of copper–ceria catalysts for water gas shift reaction in medium temperature range

A series of copper–ceria catalysts with copper loading in the range of 20–90 at% Cu (=100 × Cu/(Cu + Ce)) were prepared by the method of coprecipitation, and their performance was tested for water gas shift (WGS) reaction in medium temperature condition (150–360 °C). Both fresh and used catalysts were characterized using XRD, H₂-TPR and BET surface area measurements. After the first run, the catalysts stabilized in terms of activity and BET surface area. XRD results of used catalysts confirmed the formation of metallic Cu species during WGS reaction. The WGS activity of ceria catalysts increased with copper loading, and the synergy of copper and ceria was confirmed. Results showed 80 at% copper–ceria had the best performance. The catalysts showed stable activities at 360 °C.     

Electrochemical performances in temperature for a C-containing LiFePO4 composite synthesized at high temperature

C-LiFePO₄ composite was synthesized by mechano-chemical activation using iron and lithium phosphates and also cellulose as carbon precursor; this mixture was heated at 800 °C under argon during a short time. Long-range cyclings at different temperatures (RT, 40 and 60 °C) and at C/20 rate between 2 and 4.5 V vs. Li⁺/Li were carried out with this C-LiFePO₄ material as positive electrode material in lithium cells. Whatever the cycling conditions used, rather good electrochemical performances were obtained, with a capacity close to the theoretical one and a good cycle life, especially at RT – up to 100 cycles – and at 40 °C with ∼80% of the initial capacity maintained after 100 cycles. The electrodes recovered after long-range cyclings were characterized by X-ray diffraction; whatever the cycling temperature no significant structural changes (cell parameters, bond lengths, etc.) were shown to occur. Nevertheless, iron was found to be present at the negative electrode – as already observed by Amine et al. – after long-range cycling at 60 °C: other analyses have to be done to identify the origin of this iron (from an impurity or from LiFePO₄ itself) and to quantify this amount vs. that of active C-LiFePO₄ material using larger cells.     

Fabrication and characterization of Cu–Ni–YSZ SOFC anodes for direct use of methane via Cu-electroplating

The Cu–Ni–YSZ cermet anodes for direct use of methane in solid oxide fuel cells have been fabricated by electroplating Cu into a porous Ni–YSZ cermet anode. The uniform distribution of Cu in the Ni–YSZ anode was obtained by electroplating in an aqueous solution mixture of CuSO₄·5H₂O and H₂SO₄ for 30 min with 0.1 A of applied current. When the Cu–Ni–YSZ anode was exposed to methane at 700 °C, the amount of carbon deposited on the anode decreased as the amount of Cu in the Cu–Ni solid solution increased. The power density (0.24 W/cm²) of a single cell with a Cu–Ni–YSZ anode was slightly lower in methane at 700 °C than the power density (0.28 W/cm²) of a single cell with a Ni–YSZ anode. However, the performance of the Ni–YSZ anode-supported single cell degraded steeply over 21 h because of carbon deposition, whereas the Cu–Ni–YSZ anode-supported single cell showed enhanced durability up to 200 h.     

Hydrology,hydrochemistry and geothermal potential of El Chichón volcano-hydrothermal system,Mexico

Fluid and heat discharge rates of thermal springs of El Chichón volcano were measured using the chloride inventory method. Four of the five known groups of hot springs discharge near-neutral Na–Ca–Cl–SO₄ waters with a similar composition (Cl ∼ 1500–2000 mg kg⁻¹ and Cl/SO₄ ∼ 3) and temperatures in the 50–74 °C range. The other group discharges acidic (pH 2.2–2.7) Na–Cl water of high salinity (>15 g/L). All five groups are located on the volcano slopes, 2–3 km in a straight line from the bottom of the volcano crater. They are in the upper parts of canyons where thermal waters mix with surface meteoric waters and form thermal streams. All these streams flow into the Río Magdalena, which is the only drainage of all thermal waters coming from the volcano. The total Cl and SO₄ discharges measured in the Río Magdalena downstream from its junction with all the thermal streams are very close to the sum of the transported Cl and SO₄ by each of these streams, indicating that the infiltration through the river bed is low. The net discharge rate of hydrothermal Cl measured for all thermal springs is about 468 g s⁻¹, which corresponds to 234 kg s⁻¹ of hot water with Cl = 2000 mg kg⁻¹. Together with earlier calculations of the hydrothermal steam output from the volcano crater, the total natural heat output from El Chichón is estimated to be about 160 MWt. Such a high and concentrated discharge of thermal waters from a hydrothermal system is not common and may indicate the high geothermal potential of the system. For the deep water temperatures in the 200–250 °C range (based on geothermometry), and a mass flow rate of 234 kg s⁻¹, the total heat being discharged by the upflowing hot waters may be 175–210 MWt.     

An intermediate-temperature direct ammonia fuel cell with a molten alkaline hydroxide electrolyte

This paper describes the development and testing of a direct ammonia fuel cell utilizing a molten alkaline hydroxide electrolyte at temperatures between 200 and 450 °C. The advantages of a molten hydroxide fuel cell include the use of a highly conductive and very low-cost electrolyte, inexpensive base metal electrocatalysts, a wide operating temperature range, fuel flexibility, and fast electrode kinetics. The direct use of ammonia in such a fuel cell, even at temperatures as low as 200 °C, is made possible due to the very chemically aggressive nature of the melt. A test cell was constructed using a KOH–NaOH eutectic mixture and produced approximately 40 mW cm⁻² of power at 450 °C while operating on a stream of pure ammonia fed to the anode and compressed ambient air fed to the cathode.     

Development of LSCF–GDC composite cathodes for low-temperature solid oxide fuel cells with thin film GDC electrolyte

La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) powder was prepared by glycine–nitrate combustion method. The electrochemical properties of porous LSCF cathodes and LSCF–Gd_0.1Ce_0.9O_1.95 (GDC) composite cathodes were evaluated at intermediate/low temperatures of 500–700 °C. The polarization resistance of pure LSCF cathode sintered at 975 °C for 2 h was 1.20 Ω cm² at 600 °C. The good performance of pure LSCF cathode is attributed to its unique microstructure—small grain size, high porosity and large surface area. The addition of GDC to LSCF cathode further reduced the polarization resistance. The lowest polarization resistance of 0.17 Ω cm² was achieved at 600 °C for LSCF–GDC (40:60 wt%) composite cathode. An anode-supported solid oxide fuel cell (SOFC) was prepared using LSCF–GDC (40:60 wt%) composite as cathode, GDC film (49-μm-thick) as electrolyte, and Ni–GDC (65:35 wt%) as anode. The total electrode polarization resistance was 0.27 Ω cm² at 600 °C, which implies that LSCF–GDC (40:60 wt%) composite cathode used in the anode-supported SOFC had a polarization resistance lower than 0.27 Ω cm² at 600 °C. The cell generated good performance with the maximum power density of 562, 422, 257 and 139 mW/cm² at 650, 600, 550 and 500 °C, respectively.