Sulfonated poly(ether sulfone) for universal polymer electrolyte fuel cell operations

The performances of the proton exchange membrane fuel cell (PEMFC), direct formic acid fuel cell (DFAFC) and direct methanol fuel cell (DMFC) with sulfonated poly(ether sulfone) membrane are reported. Pt/C was coated on the membrane directly to fabricate a MEA for PEMFC operation. A single cell test was carried out using H₂/air as the fuel and oxidant. A current density of 730 mA cm⁻² at 0.60 V was obtained at 70 °C. Pt–Ru (anode) and Pt (cathode) were coated on the membrane for DMFC operations. It produced 83 mW cm⁻² maximum power density. The sulfonated poly(ether sulfone) membrane was also used for DFAFC operation under several different conditions. It showed good cell performances for several different kinds of polymer electrolyte fuel cell applications.     

Direct oxidation of jet fuels and Pennsylvania crude oil in a solid oxide fuel cell

A Cu-ceria solid oxide fuel cell (SOFC) is shown to generate electric power using jet fuels and Pennsylvania crude oil through direct oxidation of the fuels. The liquid fuels contained up to 910 ppm of sulfur and were injected into the anode compartment either with or without N₂ dilution. The performance of the fuel cell was stable over 30 h for jet fuels and Pennsylvania crude oil without N₂ dilution whereas N₂ dilution prolonged the stable power generation up to 100 h for jet fuel and up to 80 h for Pennsylvania crude oil. The generated power density was about 0.1 W cm⁻² for both fuels.     

Stabilisation of composite LSFCO–CGO based anodes for methane oxidation in solid oxide fuel cells

A La_0.6Sr_0.4Fe_0.8Co_0.2O₃–Ce_0.8Gd_0.2O_1.9 (LSFCO–CGO) composite anode material was investigated for the direct electrochemical oxidation of methane in intermediate temperature solid oxide fuel cells (IT-SOFCs). A maximum power density of 0.17 W cm⁻² at 800 °C was obtained with a methane-fed ceria electrolyte-supported SOFC. A progressive increase of performance was recorded during 140 h operation with dry methane. The anode did not show any structure degradation after the electrochemical testing. Furthermore, no formation of carbon deposits was detected by electron microscopy and elemental analysis. Alternatively, this perovskite material showed significant chemical and structural modifications after high temperature treatment in a dry methane stream in a packed-bed reactor. It is derived that the continuous supply of mobile oxygen anions from the electrolyte to the LSFCO anode, promoted by the mixed conductivity of CGO electrolyte at 800 °C, stabilises the perovskite structure near the surface under SOFC operation and open circuit conditions.     

Implementation of an UASB anaerobic digester at bagasse-based pulp and paper industry

Upflow anaerobic sludge blanket (UASB) reactor was installed to replace the conventional anaerobic lagoon treating bagasse wash wastewater from agro-based pulp and paper mill, to generate bio-energy and to reduce greenhouse gas emissions. The plant was designed to treat 12 ML d⁻¹ of wastewater having two 5 ML capacity reactors, 5.75 kg COD m⁻³ d⁻¹ organic loading rate and 20 h hydraulic retention time. In the plant 80–85% COD reduction was achieved with biogas production factor of 520 L kg⁻¹ COD reduced. In 11 months 4.4 million m³ of biogas was generated from bagasse wash wastewater utilizing UASB process. Utilization of the biogas in the Lime Kiln saved 2.14 ML of furnace oil in 9 months. Besides significant economic benefits, furnace oil saving reduced 6.4 Gg CO₂ emission from fossil fuel and conversion of the anaerobic lagoon into anaerobic reactor reduced 2.1 Gg methane emission which is equal to 43.8 Gg of CO₂.     

Optimization of water and air management systems for a passive direct methanol fuel cell

A multi-phase, multi-component, thermal and transient model is applied to simulate the operation of a passive direct methanol fuel cell and optimize the design. The model takes into consideration the thermal effects and the variation of methanol concentration at the feeding reservoir above the fuel cell. Polarization and constant current cases are numerically simulated and compared with experiments for liquid feed concentration, membrane thickness, water management and air management systems. Parameters considered when determining an optimal design include power density, fuel utilization and energy efficiencies and water balance coefficients. An optimal liquid feed concentration is determined to be 2.0 mol kg^?1, which achieved a maximum power density of 21 mW cm^?2 and a fuel utilization efficiency of 63.0%. An optimal design of a cell uses a thick membrane (Nafion 117) to reduce methanol crossover and two additional cathode GDLs to improve the water balance coefficient and efficiency of the cell. This combination results in a power density of 23.8 mW cm^?2 and a water balance coefficient of ?1.71. An air filter may also be added to improve the efficiency and water balance coefficient of the cell, however, a small loss in power density will also occur. Using an Oil Sorbents air filter the water balance coefficient is increased to ?0.85, the fuel utilization efficiency is improved by 27.35% and the maximum power density decreased to 21.6 mW cm^?2.     

Fabrication and characterization of micro tubular SOFCs for operation in the intermediate temperature

Tubular SOFC systems appear to be well-suited to accommodate repeated cycling under rapid changes in electrical load and in cell operating temperatures. Our goal is to develop innovative processing method to fabricate new micro tubular SOFCs with sub-millimeter diameter and its stack module which enable to generate high volumetric power density. In this study, micro tubular SOFCs under 1 mm diameter have been successfully fabricated and tested in the intermediate temperature region (550 °C or under). The cell consists of NiO–Gd doped ceria (GDC) as an anode (support tube), GDC as an electrolyte and (La, Sr)(Fe, Co)O₃ (LSCF)–GDC as a cathode. The single tubular cell with 0.8 mm diameter and 12 mm length generated over 70 mW at 550 °C with H₂ fuel, which indicates that the cell generated over 0.3 W cm⁻² at 550 °C.     

Sulfonic-functionalized heteropolyacid–silica nanoparticles for high temperature operation of a direct methanol fuel cell

Sulfonic-functionalized heteropolyacid–SiO₂ nanoparticles were synthesized by grafting and oxidizing of a thiol-silane compound onto the heteropolyacid–SiO₂ nanoparticle surface. The surface functionalization was confirmed by solid-state NMR spectroscopy. The composite membrane containing the sulfonic-functionalized heteropolyacid–SiO₂ nanoparticles was prepared by blending with Nafion^® ionomer. TG–DTA analysis showed that the composite membrane was thermally stable up to 290 °C. The DMFC performance of the composite membrane increased the operating temperature from 80 to 200 °C. The function of the sulfonic-functionalized heteropolyacid–SiO₂ nanoparticles was to provide a proton carrier and act as a water reservoir in the composite membrane at elevated temperature. The power density was 33 mW cm⁻² at 80 °C, 39 mW cm⁻² at 160 °C and 44 mW cm⁻² at 200 °C, respectively.     

Development of portable fuel cell arrays with printed-circuit technology

Portable hydrogen/oxygen fuel cell power sources were constructed using printed-circuit board (PCB) technology. Multiple iterations of miniature planar fuel cell devices were prototyped, demonstrating fast cycle innovation and dramatic power density improvements in <1 year of development. Several novel flow structure and gas routing designs were explored. Electrical interconnections for configurable voltage were wired on board by printed-circuit traces and vias. Fuel cell device voltages ranging from 1 V single cells to 16 V planar arrays were demonstrated, with power output ranging from <1 to >200 W. The lightweight laminate PCB technology allows the best prototypes to achieve >700 mW/cm² area power density and >400 mW/cm³ volumetric power density. PCB technology offers an intriguing platform for portable fuel cell development below 1 kW. Possibilities for on board diagnostics/control and further power density improvements are envisioned.     

Anode-supported solid oxide fuel cell based on dense electrolyte membrane fabricated by filter-coating

A simple and cost-effective technique, filter-coating, has been developed to fabricate dense electrolyte membranes. Eight mole percent yttria-stabilized zirconia (YSZ) electrolyte membrane as thin as 7 μm was prepared by filter-coating on a porous substrate. The thickness of the YSZ film was uniform, and could be readily controlled by the concentration of the YSZ suspension and the rate of the suspension deposition. The YSZ electrolyte film was dense and was well bonded to the Ni-YSZ anode substrate. An anode-supported solid oxide fuel cell (SOFC) with a YSZ electrolyte film and a La_0.85Sr_0.15MnO₃ (LSM) + YSZ cathode was fabricated and its performance was evaluated between 700 and 850 °C with humidified hydrogen as the fuel and ambient air as the oxidant. An open circuit voltage (OCV) of 1.09 V was observed at 800 °C, which was close to the theoretical value, and the maximum power density measured was 1050 mW cm⁻². The results demonstrate that the dense YSZ film fabricated by filter-coating is suitable for application to SOFCs.     

Innovative design to improve the power density of a solid oxide fuel cell

This paper explores the possibility of improving the power density of a solid oxide fuel cell (SOFC). A three-dimensional computational model (CFD-ACE package), with the relevant sub-models was used for the study. The performance of the SOFC was examined with a thin wall, which splits the inlet section and runs up to half the length of the flow channels. The results obtained with this (thin-walled) geometry were consistently better than those obtained with plain geometry (without the thin wall). The polarization characteristics of the thin-walled geometry indicated that the maximum power density obtained was 1.18 W cm⁻² at an efficiency of around 60%. The corresponding values of maximum power density and the efficiency at which it was obtained for a plain geometry were 0.88 W cm⁻² and 50%, respectively. The enhanced performance of the thin-walled geometry was attributed to a better distribution of the reactants along the length of the SOFC. Studies were also conducted to verify the performance of the thin-walled geometry over a wide range of inlet mass flow rates. They revealed a superior performance of the thin-walled geometry compared to the plain geometry. At lower inlet mass flow rates, the difference between the two in performance was small, but at higher inlet mass flow rates the difference in performance was significant.     

Effects of transport scale on heat/mass transfer and performance optimization for solid oxide fuel cells

A three-dimensional thermo-fluid–electrochemical model is developed to study the heat/mass transport process and performance of a solid oxide fuel cell (SOFC). The main objectives are to examine the transport channel size effects and to assess the potential of a thin-film-SOFC. A parametric study was performed to evaluate the channel scale effects on the temperature, species concentration, local current density and power density. The results demonstrate that decreasing the height of flow channels can lower the average solid temperature and improve cell efficiency. However, this improvement is rather limited for the smallest channels. Compared with the conventionally sized SOFC, the miniaturized SOFC with a thin-film electrolyte has the advantages of a lower operating temperature and a better performance. Based on our simulation results, the power density of a miniaturized SOFC could reach up to 5.461 W cm⁻³. However, an extremely small structure will lead to severe thermal stress induced by a large temperature gradient, a cell with a thicker rib width would have a higher efficiency and a lower average temperature. Numerical simulation is expected to help optimize the design of a solid oxide fuel cell.     

Performance of LSCF cathodes in cell tests

SOFC development at Forschungszentrum Jülich is aiming at high power density and high durability to achieve cost reduction in manufacturing and installation. For higher power density, the work on materials development has been focused on improving the cathode performance using perovskites based on (La,Sr)(Co,Fe)O_3−δ (LSCF). Materials screening and preliminary investigations were carried out with 5 cm × 5 cm cells.SOFCs with La_0.58Sr_0.4Fe_0.8Co_0.2O₃ cathodes have successfully been developed giving reproducibly a power output of 1.2 W cm⁻² at 800 °C and 0.7 V with hydrogen as fuel gas. Long-term cell tests lasting up to 3000 h revealed a degradation of the cells between 0.5 and 1.5%/1000 h of operation. This loss in performance is higher than for conventional cathodes based on (La,Sr)MnO₃ (LSM) and under further investigation to find the reason for the performance losses.     

Surface modified Nafion® membrane by ion beam bombardment for fuel cell applications

The interfacial structure between an electrolyte membrane and an electrode catalyst layer plays an important role in determining performance of proton exchange membrane fuel cell (PEMFC) since the electrochemical reactions produce electricity occur on the interfaces that are in contact with hydrogen or oxygen gas, so-called three phase boundaries. To improve performance of the PEMFC by enlarging effective area of the interfaces, surface of Nafion^® 115 membrane was roughened by Ar⁺ ion beam bombardment before being coated with a catalyst ink to form the electrode layer. With increasing ion dose density from 0 to 1 × 10¹⁷ ions cm⁻², roughness and hydrophobicity of the membrane surface increased, which could be favored for a high-performance PEMFC. In fuel cell tests, the single cell using Nafion^® membrane bombarded at an ion dose density of 10¹⁶ ions cm⁻² exhibited maximum power density of 0.62 W cm⁻², which was two times higher than that of the single cell employing untreated Nafion^® 115 membrane, i.e. 0.30 W cm⁻².     

Performance and efficiency of a DMFC using non-fluorinated composite membranes operating at low/medium temperatures

In order to increase the chemical/thermal stability of the sulfonated poly(ether ether ketone) (sPEEK) polymer for direct methanol fuel cell (DMFC) applications at medium temperatures (up to 130 °C), novel inorganic–organic composite membranes were prepared using sPEEK polymer as organic matrix (sulfonation degree, SD, of 42 and 68%) modified with zirconium phosphate (ZrPh) pretreated with n-propylamine and polybenzimidazole (PBI). The final compositions obtained were: 10.0 wt.% ZrPh and 5.6 wt.% PBI; 20.0 wt.% ZrPh and 11.2 wt.% PBI. These composite membranes were tested in DMFC at several temperatures by evaluating the current–voltage polarization curve, open circuit voltage (OCV) and constant voltage current (CV, 35 mV). The fuel cell ohmic resistance (null phase angle impedance, NPAI) and CO₂ concentration in the cathode outlet were also measured. A method is also proposed to evaluate the fuel cell Faraday and global efficiency considering the CH₃OH, CO₂, H₂O, O₂ and N₂ permeation through the proton exchange membrane (PEM) and parasitic oxidation of the crossover methanol in the cathode. In order to improve the analysis of the composite membrane properties, selected characterization results presented in [V.S. Silva, B. Ruffmann, S. Vetter, A. Mendes, L.M. Madeira, S.P. Nunes, Catal. Today, in press] were also used in the present study. The unmodified sPEEK membrane with SD = 42% (S42) was used as the reference material. In the present study, the composite membrane prepared with sPEEK SD = 68% and inorganic composition of 20.0 wt.% ZrPh and 11.2 wt.% PBI proved to have a good relationship between proton conductivity, aqueous methanol swelling and permeability. DMFC tests results for this membrane showed similar current density output and higher open circuit voltage compared to that of sPEEK with SD = 42%, but with much lower CO₂ concentration in the cathode outlet (thus higher global efficiency) and higher thermal/chemical stability. This membrane was also tested at 130 °C with pure oxygen (cathode inlet) and achieved a maximum power density of 50.1 mW cm⁻² at 250 mA cm⁻².     

Investigation of bubble effect in microfluidic fuel cells by a simplified microfluidic reactor

This study experimentally examines the influence of two-phase flow on the fluid flow in membraneless microfluidic fuel cells. The gas production rate from such fuel cell is firstly estimated via corresponding electrochemical equations and stoichiometry from the published measured current–voltage curves in the literature to identify the existence of gas bubble. It is observed that O₂ bubble is likely to be generated in Hasegawa’s experiment when the current density exceeds 30 mA cm^?2 and 3 mA cm^?2 for volumetric flow rates of 100 μL min^?1 and 10 μL min^?1, respectively. Besides, CO₂ bubble is also likely to be presented in the Jayashree’s experiment at a current density above 110 mA cm^?2 at their operating volumetric liquid flow rate, 0.3 mL min^?1. Secondly, a 1000-μm-width and 50-μm-depth platinum-deposited microfluidic reactor is fabricated and tested to estimate the gas bubble effect on the mixing in the similar microchannel at different volumetric flow rates. Analysis of the mixing along with the flow visualization confirm that the membraneless fuel cell should be free from any bubble, since the mixing index of the two inlet streams with bubble generation is almost five times higher than that without any bubble at the downstream.     

Effect of cathode current-collecting layer on unit-cell performance of anode-supported solid oxide fuel cells

According to the characterization of the microstructure and properties of solid oxide fuel cells (SOFC) electrodes, it is essential to verify various processing variables to control microstructural parameters, such as particle size, composition and spatial distribution of the constituent phases of the electrode in order to reduce the ohmic and diffusional polarization losses of the unit-cell performance. From this viewpoint, a current-collecting layer with controlled microstructure very effectively enhances the unit-cell performance by reducing the ohmic and polarization resistance of the cathode. The maximum power density of a 5 cm × 5 cm unit-cell with the controlled current-collecting layer is ∼1.5 W cm⁻² at 750 °C, while a unit-cell without the layer is much lower, viz., 0.9 W cm⁻².     

The role of ambient conditions on the performance of a planar,air-breathing hydrogen PEM fuel cell

This paper presents experimental data on the effects of varying ambient temperature (10–40 °C) and relative humidity (20–80%) on the operation of a free-breathing fuel cell operated on dry-hydrogen in dead ended mode. We visualize the natural convection plume around the cathode using shadowgraphy, measure the gas diffusion layer (GDL) surface temperature and accumulation of water at the cathode, as well as obtain polarization curves and impedance spectra. The average free-convection air speed was 9.1 cm s⁻¹ and 11.2 cm s⁻¹ in horizontal and vertical cell orientations, respectively. We identified three regions of operation characterized by increasing current density: partial membrane hydration, full membrane hydration with GDL flooding, and membrane dry-out. The membrane transitions from the fully hydrated state to a dry out regime at a GDL temperature of approximately 60 °C, irrespective of the ambient temperature and humidity conditions. The cell exhibits strong hysteresis and the dry membrane regime cannot be captured by a sweeping polarization scan without complete removal of accumulated water after each measurement point. Maximum power density of 356 mW cm⁻² was measured at an ambient temperature of 20 °C and relative humidity of 40%.     

Increasing the operation temperature of polymer electrolyte membranes for fuel cells: From nanocomposites to hybrids

Among the possible systems investigated for energy production with low environmental impact, polymeric electrolyte membrane fuel cells (PEMFCs) are very promising as electrochemical power sources for application in portable technology and electric vehicles. For practical applications, operating FCs at temperatures above 100 °C is desired, both for hydrogen and methanol fuelled cells. When hydrogen is used as fuel, an increase of the cell temperature produces enhanced CO tolerance, faster reaction kinetics, easier water management and reduced heat exchanger requirement. The use of methanol instead of hydrogen as a fuel for vehicles has several practical benefits such as easy transport and storage, but the slow oxidation kinetics of methanol needs operating direct methanol fuel cells (DMFCs) at intermediate temperatures. For this reason, new membranes are required. Our strategy to achieve the goal of operating at temperatures above 120 °C is to develop organic/inorganic hybrid membranes. The first approach was the use of nanocomposite class I hybrids where nanocrystalline ceramic oxides were added to Nafion. Nanocomposite membranes showed enhanced characteristics, hence allowing their operation up to 130 °C when the cell was fuelled with hydrogen and up to 145 °C in DMFCs, reaching power densities of 350 mW cm⁻². The second approach was to prepare Class II hybrids via the formation of covalent bonds between totally aromatic polymers and inorganic clusters. The properties of such covalent hybrids can be modulated by modifying the ratio between organic and inorganic groups and the nature of the chemical components allowing to reach high and stable conductivity values up to 6.4 × 10⁻² S cm⁻¹ at 120 °C.     

Effects of sputtering parameters on the performance of electrodes fabricated for proton exchange membrane fuel cells

One way to alleviate the emission of air pollutants and CO₂ due to burning fossil fuels is the use of fuel cells. Sputter deposition techniques are good candidates for the fabrication of electrodes used for proton exchange membrane fuel cells (PEMFCs). Input power and sputtering-gas pressure are two important parameters in a sputtering process. However, little is known about the effects of these sputtering parameters on the performance of PEMFC electrodes. Therefore, this study applied a radio frequency (RF) magnetron sputter deposition process to prepare PEMFC electrodes and investigated the effects of RF power and sputtering-gas pressure in electrode fabrication on electrode/cell performance. At a Pt loading of 0.1 mg cm⁻², the electrode fabricated at 100 W, 10⁻³ Torr was found to exhibit the best performance mainly due to its lowest kinetic (activation) resistance (dominating the cell performance) in comparison to those fabricated by 50 and 150 W at 10⁻³ Torr, as well as by 10⁻⁴ and 10⁻² Torr at 100 W. In the tested ranges, the control of sputtering-gas pressure seems to be more critical than that of RF power for the activation loss. In addition to electrochemically active surface area, electrode microstructure should also be responsible for electrode/cell polarization, particularly the activation polarization.     

Improvement of anode performance by surface modification for solid oxide fuel cell running on hydrocarbon fuel

A Ni/ yttria-stabilized zirconia (YSZ) cermet anode was modified by coating with samaria-doped ceria (SDC, Sm_0.2Ce_0.8O₂) sol within the pores of the anode for a solid oxide fuel cell (SOFC) running on hydrocarbon fuel. The surface modification of Ni/YSZ anode resulted in an increase of structural stability and enlargement of the triple phase boundary (TPB), which can serve as a catalytic reaction site for oxidation of carbon or carbon monoxide. Consequently, the SDC coating on the pores of anode made it possible to have good stability for long-term operation due to low carbon deposition and nickel sintering.The maximum power density of an anode-supported cell (electrolyte; 8 mol% YSZ and thickness of 30 μm, and cathode; La_0.85Sr_0.15MnO₃) with the modified anode was about 0.3 W/cm² at 700 °C in the mixture of methane (25%) and air (75%) as the fuel and air as the oxidant. The cell was operated for 500 h without significant degradation of cell performance.