Aim of this work is to model and study the behavior of thermocouples as they are used in the measurement of gas temperatures in solid oxide fuel cell systems. Due to the high temperature regime in such systems, the effect of radiation and conduction from surrounding solids may bias the measurements with important consequences on control, performance, and cell durability. In order to study these effects a mathematical model of a working thermocouple was developed and it was integrated in that of a heat exchanger, which was part of a larger SOFC system. The enhanced heat exchanger's model was then validated with measurements from a test on a real system. The possibility to overcome the bias and to have a more correct approximation of the real gas temperatures is discussed.

The chemical stability of perfluorinated and non-perfluorinated low temperature fuel cell model compounds (MCs) against attack by hydroxyl radicals, HO^•, is compared using a competition kinetics approach in aqueous solutions at ambient temperature. HO^• radicals were generated in situ by UV photolysis of hydrogen peroxide in the electron spin resonance (ESR) resonator. Acetic acid (AA), trifluoroacetic acid (TFAA), methanesulfonic acid (MSA), trifluorosulfonic acid (TFSA), and perfluoro(2-ethoxyethane)sulfonic acid (PFEESA) were chosen as MCs, while the rate constants of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and methanol (CH₃OH) served as reference for the determination of relative rate constants by means of steady state ESR signal amplitudes. In decreasing order the rate constants are: k_MSA = (4.8 ± 0.2) × 10⁷ M^–1 s^–1, k_AA = (4.2 ± 0.3) × 10⁷ M^–1 s^–1, k_PFEESA = (3.7 ± 0.1) × 10⁶ M^–1 s^–1, k_TFAA = (7.9 ± 0.2) × 10⁵ M^–1 s^–1, and k_TFSA < 1.0 × 10⁵ M^–1 s^–1. Applying these results to perfluorinated fuel cell membranes like Nafion®, the main points of attack by HO^• are concluded to be the ether groups of the side chains, followed by the remaining carboxyl groups from the manufacturing process of the polymers.

Fuel cells with BaZr_0.1Ce_0.7Y_0.2O_3–δ (BZCY) proton-conducting electrolyte is fabricated using spray-modified pressing method. In the present study the spray-modified pressing technology is developed to prepare thin electrolyte layers on porous Ni-BZCY anode supports. SEM data show the BZCY electrolyte film is uniform and dense, well-bonded with the anode substrate. An anode-supported fuel cell with BZCY electrolyte and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ (BSCF) cathode is characterized from 600 to 700 °C using hydrogen as fuel and ambient air as oxidant. Maximum power density of 536 mW cm^–2 along with a 1.01 V OCV at 700 °C is obtained. Impedance spectra show that Ohmic resistances contribute minor parts to the total ones, for instance, only ~23% when operating at 600 °C. The results demonstrate that spray-modified pressing technology offers a simple and effective way to fabricate quality electrolyte film suitable to operate in intermediate temperature.

Solid oxide fuel cells (SOFCs) have the potential to meet the critical energy needs of our modern civilization and minimize the adverse environmental impacts from excessive energy consumption. They are highly efficient, clean, and can run on variety of fuel gases. However, little investigative focus has been put on optimal power output based on electrode microstructure. In this work, a complete electrode polarization model of SOFCs has been developed and utilized to analyze the performance of functionally graded anode with different particle size and porosity profiles. The model helps to understand the implications of varying the electrode microstructure from the polarization standpoint. The work identified conditions when grading can improve the cell performance and showed that grading is not always beneficial or necessary.

An artificial neural network (ANN) and a genetic algorithm (GA) are employed to model and optimize cell parameters to improve the performance of singular, intermediate-temperature, solid oxide fuel cells (IT-SOFCs). The ANN model uses a feed-forward neural network with an error back-propagation algorithm. The ANN is trained using experimental data as a black-box without using physical models. The developed model is able to predict the performance of the SOFC. An optimization algorithm is utilized to select the optimal SOFC parameters. The optimal values of four cell parameters (anode support thickness, anode support porosity, electrolyte thickness, and functional layer cathode thickness) are determined by using the GA under different conditions. The results show that these optimum cell parameters deliver the highest maximum power density under different constraints on the anode support thickness, porosity, and electrolyte thickness.

A new design of High Temperature Steam Electrolyzer (HTSE) based on metallic seals, associated to an insulating cell support and a flexible interconnect system has been proposed. In this work, complete simulations of this 3D design have been performed with ANSYS®-FLUENT® software. The temperature repartition is determined by taking into account thermal exchanges, fluids movements, and electrochemical reactions. Moreover, due to stress relaxation mechanism, the flexible interconnect loading decreases during time, which may impact the contact resistance and the electrochemical solution. A possible degradation of the contact resistance with time is predicted by the simulation and its effect will be discussed according to some design parameters. Steam electrolysis tests have been conducted at 800 °C on this new design. The comparisons to the simulations are also presented. All these results obtained in this study lead to propose some recommendations for such a design.

A composite catalyst has been successfully prepared by dispersing Pt nanoparticles on a poly(o-dihydroxybenzene) (PoDHB) modified glassy carbon (GC) electrode and characterized by SEM, EDX, and electrochemical analysis. Compared with Pt nanoparticles deposited on the bare GC, the Pt/PoDHB/GC exhibits higher catalytic activity and stronger poisoning tolerance for electro-oxidation of methanol and formic acid. The enhanced performance could be attributed to the increase of electrochemical active surface area (EASA) arisen from the PoDHB modification. Furthermore, performance limiting factors such as platinum loading, polymer mass, H₂SO₄, methanol, and formic acid concentrations have been evaluated for optimizing the electrocatalytic activities.

Molybdenum carbide (MoC) and tungsten carbide (WC) are synthesized by direct carbonization method. Pt–Ru catalysts supported on MoC, WC, and Vulcan XC-72R are prepared, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy in conjunction with electrochemistry. Electrochemical activities for the catalysts towards methanol electro-oxidation are studied by cyclic voltammetry. All the electro-catalysts are subjected to accelerated durability test (ADT). The electrochemical activity of carbide-supported electro-catalysts towards methanol electro-oxidation is found to be higher than carbon-supported catalysts before and after ADT. The study suggests that Pt–Ru/MoC and Pt–Ru/WC catalysts are more durable than Pt–Ru/C. Direct methanol fuel cells (DMFCs) with Pt–Ru/MoC and Pt–Ru/WC anodes also exhibit higher performance than the DMFC with Pt–Ru/C anode.

The performance of solid oxide cells (SOCs) heavily relies on the population of three-phase boundaries (TPBs) in the composite electrodes. In this study, SOC composite electrodes are described by percolating binary particle aggregates that are constructed from random loose packing models and classical sintering theories. Summed perimeters of the sintering necks represent the total TPB lengths. A case study has been carried out on lanthanum strontium manganite (LSM)–yttria-stabilized zirconia (YSZ) composite electrodes. By employing three-dimensional data that are converted from relevant two-dimensional data, the TPB length of baseline LSM–YSZ electrodes investigated in this study is 35.4 μm μm^–3. The parametric and sensitivity analyses show the changes of TPB lengths in functions of the weight fraction of powders, particle size and particle size ratio of powders, void fraction of electrodes, and density of materials. In the case of baseline LSM–YSZ electrodes, proper electrode design and optimization would result in 2–3 times of the enlargement of TPBs. Technical guidelines on the design and optimization of SOC composite electrodes are proposed.

Poly(2,2′-imidazole-5,5′-bibenzimidazole) (PBI-imi) was synthesized via the polycondensation between 3,3′,4,4′-tetraaminobiphenyl and 4,5-imidazole-dicarboxylic acid. Effects of the reaction conditions on the intrinsic viscosity of the synthesized polymers were studied. The results show that the molecular weight of the polymers increases with increasing monomer concentration and reaction time, and then levels off. With higher reaction temperature, the molecular weight of the polymer is higher. With the additional imidazole group in the backbone, PBI-imi shows improved phosphoric acid doping ability, as well as a little higher proton conductivity when compared with widely used poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI-ph).Whereas, PBI-imi and PBI-ph have the similar chemical oxidation stability. PBI-imi/3.0 H₃PO₄ composite membranes exhibit a proton conductivity as high as 10^–4 S cm^–1 at 150 °C under anhydrous condition. The temperature dependence of proton conductivity of acid doped PBI-imi can be modeled by an Arrhenius equation.

In this work, a kind of thin K-type thermocouple and self-developed CAS-I sealant were used to assembly solid oxide fuel cell (SOFC) stacks and temperatures of unit cells inside a planar SOFC stack were measured. The open circuit voltage testing of the stack and characterization of the interface between sealant and components suggested excellent sealing effect by applying the developed method. The effect of discharging direct-current on temperature and temperature distribution inside the designed SOFC stack was investigated. The results showed that the discharging current had a great impact and the gas flow rate had a slight impact on the temperatures of unit cells. Temperature distribution of unit cells inside the stack was much non-uniform and there is a significant temperature difference between various components of the stack and heating environment. The relationship between temperatures and cell performance showed that the worse the cell performance, the higher the cell surface temperature. When the stack was discharged at a constant current and the temperature of cell surface was over 950 °C, the higher the temperature, the more drop the corresponding voltage.

The alcohols (methanol, ethanol, and 1-propanol) crossover behavior of through fuel cell membrane electrode assembly (MEA) in direct alcohol fuel cell (DAFC) system was studied. We divided five different factors which affect alcohol crossover behavior through MEA to analyze alcohol crossover behavior. Those are membrane effect, physical blocking effect of anode, alcohol oxidation effect of anode electrocatalysts, physical blocking effect of cathode, and alcohol oxidation effect of cathode. Among these five factors, the four factors caused by two different electrodes (anode and cathode) were evaluated by fabricating various types of MEA. In the case of alcohols through membrane without any electrode was increased when the cell temperature was raised from room temperature to 100 °C, but it was decreased above the cell temperature of 100 °C. Among the electrode effects on alcohol crossover rate, physical blocking effect of electrodes played dominant role below 100 °C. However alcohol oxidation effects of electrodes was predominant above the 100 °C.

With the aim of investigating the microwave influence on the electrolyte material properties, La_0.80Sr_0.20Ga_0.83Mg_0.17O_2.815 was prepared by both a conventional and a microwave-assisted sol–gel Pechini method. With respect to the conventional Pechini method (hereafter SGP), the microwave assisted process (hereafter MWA-SGP) guaranteed a faster procedure, reducing the time needed to remove the excess solvents to complete the polyesterification reaction from some days to a few hours. In fact, when a MWA-SGP method was used, powders having higher phase purity were obtained. The sintering process at 1,450 °C of the powders prepared by both methods yielded pellets with similar density values (≥92% of theoretical). Nevertheless, only by microwave-assisted process single-phase products were obtained and no secondary phases such as tetragonal LaSrGaO₄ and LaSrGa₃O₇ were detected. These by-products have been demonstrated to be detrimental for conductivity. Indeed, pellets obtained by MWA-SGP method showed oxygen ionic conductivity values higher (about 30–40%) than those checked for SGP samples, thus demonstrating the important role of the microwave process on reducing time and costs and on improving the electrolyte properties.

Four cathode materials for single chamber solid oxide fuel cell (SC-SOFC) [La_0.8Sr_0.2MnO_3–δ (LSM), Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ (BSCF), Sm_0.5Sr_0.5CoO_3–δ (SSC), and La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF)] were investigated regarding their chemical stability, electrical conductivity, catalytic activity, and polarization resistance under air and methane/air atmosphere. Electrolyte-supported fuel cells, with Ce_0.9Gd_0.1O_2–δ (CGO) electrolyte and a Ni-CGO anode, were tested in several methane/air mixtures with each cathode materials between 625 and 725 °C. These single cells were not optimized but only designed to compare the four studied cathodes. The decrease of methane-to-oxygen ratio from 2 to 0.67 strongly increased the performance of fuel cells for all cathode materials but the effect of temperature was not always significant. Cells with SSC, BSCF, and LSCF have shown a maximum power density about 20 mW cm^–2 while the cell with LSM has given only 5 mW cm^–2.

The structure, electrical conduction, thermal expansion and electrochemical properties of the La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ + La₂NiO_4+δ (LSCF-LNO) composite cathodes were investigated with regard to the volume fraction of the LNO composition. No chemical reaction product between the two constituent phases was found for the composite cathodes sintered at 1,400 °C for 10 h within the sensitivity of the XRD. Compared to the performance of the LSCF cathode, the LNO composition in the composite cathode plays a role in deteriorating both electrical conductivity and electrochemical properties, however, improving the thermal expansion properties. The trade-off between electrical conducting and thermal expansion classifies the composite cathode containing 30 volume percent (vol.%) LNO as the optimum composition. For characterizing cathode performance in a single cell, a slurry spin coating technique was employed to prepare a porous cathode layer as well as a YSZ/Ce_0.8Sm_0.2O_3–δ (SDC) electrolyte. The optimum conditions for fabricating the YSZ/SDC electrolyte were investigated. The resulting single cell with 70 vol.% LSCF-30 vol.%LNO (LSCF-LNO30) cathode shows a power density of 497 mW cm^–2 at 800 °C, which is lower than that of the cell with a LSCF cathode, but still within the limits acceptable for practical applications.

The structural integrity of the sealing material is critical for the reliability of solid oxide fuel cell stacks. In this respect failure and deformation are aspects which need to be assessed in particular for glass ceramic sealant materials. Bending tests were carried at room temperature and typical stack operation temperature for glass ceramic sealants with different crystallization levels. Elastic moduli, fracture stresses, and viscosity values are reported. In addition to sintered bars some bending testing were carried out for steel specimens that were head-to-head joined with the glass ceramics similar as in a stack application. The ceramic particle reinforced sealant material was screen printed onto the steel. The results reveal a decrease of the strength for the partially crystallized sealant at operation relevant temperatures that can be associated with the viscous deformation of the material.

Single-chamber solid oxide fuel cell (SC-SOFC) microstacks with V-Shaped congener-electrode-facing configuration were fabricated and operated successfully in a box-like stainless steel chamber. Two gas channels with small gas inlets were used to transport the fuel and oxygen to the anodes and cathodes, respectively. The temperature of an anode-facing-anode two-cell stack was higher than that of a cathode-facing-cathode two-cell stack during the test procedure. For a three-cell stack, the cell in the middle region presented the highest power output. The open circuit voltage (OCV) and maximum power output of the three-cell stack in a gas mixture of 100 sccm N₂, 120 sccm CH₄, and 80 sccm O₂ were 3.0 V and 413 mW, respectively.

Effect of the orientation of cylindrical pores within an anode has been studied on the performance of anode-supported solid oxide fuel cell (SOFC). Paper-fibers are used as pore-former and highly oriented cylindrical pores are formed within the anode prepared by uniaxial compaction. A thick anode brick is fabricated followed by cutting in different directions to obtain anode substrates with desirable orientation of pores. When the orientation of cylindrical pores is perpendicular to the anode surface, the gas transport is significantly improved so that the reduction rate of the NiO/YSZ anode is considerably accelerated and the cell concentration polarization is minimized. The corresponding single cell exhibits a maximum power density as high as 1.54 W cm^–2 in hydrogen and 0.90 W cm^–2 in nitrogen diluted methane at 800 °C. The result indicates that the output performance of anode-supported cells could be significantly improved by manipulating the orientation of pores.

Investigation of the cathode reaction in solid oxide fuel cells (SOFC) by impedance spectroscopy (IS) measurements using evolutionary-based programming analysis is demonstrated. In contrast to the conventional analysis methods used for impedance spectroscopy measurements, e.g., equivalent circuits, the impedance spectroscopy genetic programming (ISGP) program seeks for a distribution of relaxation times that has the form of a peak or a sum of several peaks, assuming the Debye kernel. Using this method one finds a functional (parametric) form of the distribution of relaxation times. A symmetric cell configuration of Pt|LSCF|GDC|LSCF|Pt was examined using IS measurements combined with I–V measurements. Different samples at different temperatures and different oxygen partial pressures were examined in order to investigate their influence on the oxygen reduction reaction. The resulting IS data was analyzed using the ISGP program and the resulting peaks constructing the distribution of relaxation times were assigned for the different processes that occur at the cathode side. The activation energies as well as the dependence of the processes on the oxygen partial pressure were also evaluated.

Adequate water management is critical in proton exchange membrane fuel cells for improving performance and durability. In this paper, we present results of experiments allowing to quantify the effect of a temperature difference between anode and cathode flow field plates on the transport of water. The results confirm the existence of a temperature-gradient driven flux between the anode and cathode compartments. They show the strong interplay between water management and heat management and they confirm that water flows mostly in vapor form through the porous media of the MEA. Apart from the current density and the difference between the temperature of the electrodes and of the flow field plates, the water flux in the direction perpendicular to the membrane is also (weakly) dependent on the humidification of the gases. No significant effect has been measured as a function of the GDL thickness as well as of the presence or absence of a MPL. However, using a MPL improves significantly the performance of the fuel cell.

The effect of cerium substitution on the electrical and electrochemical characteristics of a new anode material La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM) was examined by synthesizing Ce_xLa_0.75–xSr_0.25Cr_0.5Mn_0.5O₃ for x = 0–0.375). From x = 0–0.25, the structure is rhombohedral (S.G. R-3c), and with a higher cerium content (x = 0.375) it becomes cubic (S.G. Pm-3m). These materials are stable in the operating conditions of an SOFC anode. Ce_xLa_0.75–xSr_0.25Cr_0.5Mn_0.5O₃ and LSCM materials are p-type semi-conductors. Cerium substitution improves the conductivity in neutral atmosphere from 18.3 to 35.4 S cm^–1 for x = 0 and 0.375, respectively, at 1,173 K. In reducing conditions, the conductivity is not influenced by cerium substitution, and it is about 1 S cm^–1 at 1,173 K. High temperature XRD shows that structure becomes cubic at 1,073 K in operating (reducing) conditions. Cerium substitution positively enhances the electrochemical behavior, as proved by studying the properties of dense cone-shaped electrodes.

Our goal in the present work was to synthesize a new proton exchange membrane that could be used in proton exchange membrane fuel cell (PEMFC), based on a blend of sulfonated polyethersulfone (S-PES) and sulfonated polyethersulfone octylsulfonamide (S-PESOS). Five blends, using S-PESOS with different grafting ratios of sulfonamide groups, have been elaborated, characterized, and tested in a PEMFC. The similar chemical structure between these two polymers favored their compatibility. The synthesized membranes showed a high water swelling capacity and an ionic conductivity equivalent to that of Nafion® (0.1 S cm^–1) in the same conditions.

We report the design of a H₂/O₂ (fuel) cell for in situ μ-Raman spectroscopic measurements. The horizontal orientation of the cell is conceived to allow the penetration of the laser beam along the z-axis from one electrode to the other. We show that during in-depth analyses the Raman signal is not significantly lost and the axial resolution is sufficiently good to allow quantitative and qualitative spectral interpretation. We report “proof of principle” tests performed on Nafion membranes swelled with protic ionic liquids to demonstrate the validity of the design and the potentiality of the method. Our results confirm that this experimental setup can efficiently be used to follow structural changes and concentration gradients in the electrolyte of a fuel cell operando. In particular, we have been able to resolve both in time and in space the hydration state of the membrane as well as spatial variations for the coordination shell during a compositional transient state.

Thanks to their high conductivity, important gas tightness, good corrosion resistance, and low-cost manufacturing pathways, stainless steels are considered as good candidates for proton exchange membrane fuel cell (PEMFC) bipolar plates materials. In this study, a proprietary alloy was identified as very promising: its initial electrical contact resistance (ECR) with the gas diffusion layer was low, while its corrosion resistance in simulated PEMFC environment was sufficient. Furthermore, the ECR did not increase dramatically during long-term potentiostatic and potentiodynamic polarizations in simulated PEMFC cathode and anode environments. Finally, the stainless steel was successfully tested for 3,000 h in a commercial system using a 16-cell stack, without detrimental cell voltage losses.

This work investigates the catalytic properties of Ir/Ce_0.9Gd_0.1O_2–x (Ir/CGO) catalyst and CGO support in steam reforming of methane in the absence or presence of H₂S (50 ppm) for further application in a solid oxide fuel cell (SOFC) working under methane at intermediate temperatures and integrating a gradual internal reforming concept. The catalytic activity was measured at 750 °C by using a 50 mol.% CH₄/5 mol.% H₂O/45 mol.% N₂ mixture and a 10 mol.% CH₄/90 mol.% N₂ mixture. The addition of Ir to CGO improves the catalytic activity in hydrogen production by two orders of magnitude with respect to that of CGO alone. Temperature programmed oxidation experiments were performed after reaction in both types of mixtures to study the eventual formation of carbon deposits. Over Ir/CGO, carbon formed in little amounts (even in the absence of H₂O in the feed), being highly reactive toward O₂. Upon H₂S addition, the CGO support exhibited surprisingly an improved catalytic activity on the contrary to Ir/CGO which partly deactivated. Upon suppression of H₂S in the feed the initial catalytic activity was fully restored for both catalysts. The catalytic behavior of CGO in the presence of H₂S was discussed, based upon temperature programmed reaction of CH₄.

The evolution of membrane water concentration profile has been studied by small angle neutron scattering during on/off cycling PEMFC operation with fully humidified air in co-flow configuration. The water concentration profiles during on/off cycling evolve in opposite ways close to the gas inlet and outlet. Whereas the global membrane water content increases at the gas inlet as the fuel cell delivers current, the membranes are dried out at the gas outlet. The balance between the diffusion of water from cathode to anode and the electroosmostic drag from anode to cathode gives a net flow which is different close to the gas inlet and gas outlet. The equilibrium is reached in less than 15 min and it is faster when the fuel cell is switched on that is to say when a proton flows is imposed. Moreoever, the time to equilibrium decreases as the membrane content is increased.

The effect of compressive stress on the local water content of Nafion NRE 212 and Aquivion E79 membranes is studied by confocal μ-Raman spectroscopy using a specific tightening device. This device aims to mimic the geometry of the bipolar plate flow field of actual fuel cells, i.e. the sequence of channels and ribs. The membrane water content decreases with increasing stress, under the ribs as well as in the channel. The higher the initial water content, the larger the water content decreases with mechanical stress. The extent of water loss depends on the position of the membrane in the device, the applied stress and the hydration history of the membrane.

There is an increasing demand of multifunctional materials for a wide variety of technological developments. Bipolar plates for proton exchange membrane fuel cells are an example of complex functionality components that must show among other properties high mechanical strength, electrical, and thermal conductivity. The present research explored the possibility of using alumina–carbon nanofibers (CNFs) nanocomposites for this purpose. In this study, it was studied for the first time the whole range of powder compositions in this system. Homogeneous powders mixtures were prepared and subsequently sintered by spark plasma sintering. The materials obtained were thoroughly characterized and compared in terms of properties required to be used as bipolar plates. The control on material microstructure and composition allows designing materials where mechanical or electrical performances are enhanced. A 50/50 vol.% alumina–CNFs composite appears to be a very promising material for this kind of application.

Graphitised carbon nanofibres (G-CNFs) show superior thermal stability and corrosion resistance in PEM fuel cell environment over traditional carbon black (CB) and carbon nanotube catalyst supports. However, G-CNFs have an inert surface with only very limited amount of surface defects for the anchorage of Pt catalyst nanoparticles. Modification of the fibre surface is therefore needed. In this study Pt nanoparticles have been deposited onto as-received and surface-modified G-CNFs. The surface modifications of the fibres comprise acid treatment and nitrogen doping by pyrolysis of a polyaniline (PANI) precursor. The modified surfaces were studied by FTIR and XPS and the electrochemical characterization, including long-term Pt stability tests, was performed using a low-temperature PEMFC single cell. The performance and stability of the G-CNF supported catalysts were compared with a CB supported catalyst and the effects of the different surface treatments were discussed. On the basis of these results, new membrane electrode assemblies (MEAs) were manufactured and tested also for carbon corrosion by in situ FTIR analysis of the cathode exhaust gases. It was observed that the G-CNFs showed 5 times lower carbon corrosion compared to CB based catalyst when potential reached 1.5 V versus RHE in simulated start/stop cycling.

To enable a large penetration of proton exchange membrane fuel cells (PEMFC) on the market, the durability of these systems must be improved. This work aims at evaluating the durability of carbon aerogels used as cathode catalyst support and at comparing it with the durability of a commercial electrocatalyst Tanaka Kikinzoku Group (TKK). To do so, platinum was deposited on carbon aerogel. Resulting electrocatalysts were then used to prepare 50 cm² membrane electrode assemblies (MEA). MEAs were then submitted to an ageing protocol consisting in operating the cell under H₂/N₂ and in maintaining the cell potential at 1.2 V during cycles of 7 h. MEA performance was then evaluated every 7 h before the following cycle. We showed that, in our testing conditions, neither carbon aerogel nor the commercial electrocatalyst can fulfil DOE objectives in terms of durability. The lower carbon aerogel corrosion resistance as compared to that one of the commercial electrocatalyst can be explained by their low degree of graphitisation. Carbon aerogels durability could be increased thanks to a pyrolysis at higher temperatures.

The electrooxidation of methanol was studied at elevated temperature and pressure by cyclic voltammetry and constant potential experiments at real fuel cell electrocatalysts. Ruthenium core and platinum shell nanoparticles were synthesized by a sequential polyol route, and characterized electrochemically by CO stripping at room temperature to quickly confirm the structure of the synthesized core–shell structure as compared to pure commercial Pt/C and Pt–Ru/C alloy catalysts. A significant promotional effect of Pt decorated Ru cores in the methanol oxidation was found at elevated temperatures and rather high-electrode potentials. A negative potential shift of the methanol oxidation peak is observed for the Ru@Pt/C core–shell catalyst at moderate temperatures, while a significant shift to positive potentials of the methanol oxidation peak occurs for Pt/C catalysts. The onset potential for methanol oxidation is lowered some 200 mV from room temperature and up to 120 °C for all electrocatalysts, indicating that it is the thermal activity of water adsorption that dictates the onset potential. Direct methanol fuel cell experiments showed only small performance differences between Ru@Pt/C and Pt/C anode electrocatalysts, suggesting the necessity of render possible the formation of surface oxygen species at lower electrode potentials.

Polybenzimidazole membranes imbibed with acid are emerging as a suitable electrolyte material for high-temperature polymer electrolyte fuel cells. The oxidative stability of polybenzimidazole has been identified as an important issue for the long-term durability of such cells. In this paper the oxidative degradation of the polymer membrane was studied under the Fenton test conditions by the weight loss, intrinsic viscosity, size exclusion chromatography, scanning electron microscopy and Fourier transform infrared spectroscopy. During the Fenton test, significant weight losses depending on the initial molecular weight of the polymer were observed. At the same time, viscosity and SEC measurements revealed a steady decrease in molecular weight. The degradation of acid doped PBI membranes under Fenton test conditions is proposed to start by the attack of hydroxyl radicals at the carbon atom linking imidazole ring and benzenoid ring, which may eventually lead to the imidazole ring opening and formation of small molecules and terminal groups for further oxidation by an endpoint oxidation.

Building on the improved proton conductivity at intermediate temperatures under anhydrous conditions using a ‘proton donor–proton acceptor' concept demonstrated for the first time in the composite membrane made of inorganic lewis acid (boron-based electron-deficient nanoparticles) and a poly-[(1-(4,4′-diphenylether)-5-oxybenzimidazole)-benzimidazole] (PBI-OO)/perfluorosulfonic acid (PFSA) blend, we report here the thermal behaviours and direct methanol fuel cell (DMFC) single cell performance of these membranes at intermediate temperatures (90–120 °C). It is found that the PFSA/PBI-OO blends and PFSA/PBI-OO/nano-BN composites show decreased thermal stability compared to pristine PFSA. We attribute this to a proton transfer reaction between the sulfonic acid and imidazole moieties of the constituent polymers inducing a decreased stability of the resulting sulfonate group. When operated with dry oxygen and methanol/water vapour, the single cell performance of PFSA/PBI-OO blends is slightly improved compared to that of pristine PFSA. The PFSA/PBI-OO/nano-BN composite membranes exhibit much better single cell performance at intermediate temperatures, which could be mainly attributed to its higher anhydrous proton conductivity.

In the present work two 3-D models, for the catalytic layer, were employed in order to simulate the responses of a PBI high temperature polymeric membrane fuel cell. The simulations made use of an agglomerate model and a pseudo-homogenous model, both implemented taking into account the temperature influence over their parameters. The overall simulation was performed also as two models, linked by the variable pressure, one for the whole graphite plate simulating the distribution channels, and the other dealing with the MEA and thereof the catalytic layer. A discussion over the two models was done and the experimental results demonstrated that the pseudo-homogeneous obtained the better fits.

The U.S. Department of Energy Fuel Cell Technologies Program supports research and development (R&D) of fuel cells and fuel cell systems for stationary, portable and transportation applications. The Program maintains a diverse portfolio of R&D projects aimed at reducing cost and improving durability of fuel cell systems, with an overarching goal of enabling fuel cell technology to compete with alternative technologies in the marketplace. This paper describes the Program's recent activities and progress in development of catalysts, membranes and membrane electrode assemblies for polymer electrolyte membrane fuel cells.

Multiblock-co-polymers with different ion exchange capacities were synthesised by nucleophilic aromatic step-growth polycondensation of hydrophilic and hydrophobic oligomers. The main focus of this work was to investigate the dependence of oligomer reactivity on molecular weight and how the reaction conditions need to be changed to obtain high-molecular multiblock-co-polymers, consisting of long block segments. Multiblock-co-polymers composed of short oligomers could be synthesised under mild reaction conditions. The coupling of longer oligomers required more basic reaction conditions, because the reactive functional end-groups were shielded by the long oligomeric main chain. The membranes were investigated further in terms of their properties relevant for use as polymer electrolyte membrane in direct methanol fuel cells (DMFCs). The mechanical stability of the acidic polymers was improved through ionical crosslinking with basic polybenzimidazole. A series of membranes was tested in a self- and in an air-breathing DMFC.

Na-X zeolites particles, synthesized in two size ranges, namely 200–300 nm and 30–100 nm, were used to prepare Nafion/Na-X zeolite composite membranes by recast method. The physical, chemical, and morphological properties of the zeolite powders and composite membranes were examined by XRD, N₂ adsorption isotherms, FTIR, SEM, and SAXS analysis. Furthermore, the effect of zeolite particles size and loadings (i.e., 5 and 10% w/w) on the water, methanol, and proton transport properties was investigated.

It has been found that the size of the Na-X zeolite particles plays a key role in the proton and methanol transport behavior since it rules the zeolite hydrophilic behavior, the morphology of polymer–filler interphase, and also the nature of water established in the composite membrane.

The results show that the membranes loaded with a 5% w/w of submicron-sized Na-X zeolite exhibit a proton conductivity and selectivity significantly higher than Nafion. In particular the proton conductivity at 120 °C is around eight times and the selectivity at 25 °C is around 40% higher than those exhibited by recast Nafion.

It has now been well recognized that both the performance and durability of proton exchange membrane fuel cells (PEMFCs) are closely related to the water accumulation and transport inside its porous components, particularly in the gas diffusion layer (GDL), and microporous layer (MPL). In this paper, the key GDL and MPL properties that affect water transport through them are first discussed and a review of GDL degradation mechanisms is presented. An intermittent water drainage mechanism across the GDL is discussed. The capillary breakthrough pressure (CBP) and the dynamic capillary pressure (DCP), or recurrent breakthrough dynamics, have been identified as key GDL properties that affect its water management performance and function as indicators of the degradation of GDL material. This work uses a novel ex situ experiment to degrade a GDL by exposing it to an accelerated stress test (AST) that subjects the GDL to elevated operation conditions seen at the cathode side of a PEMFC for an extended period of time. In turn, the effect of the AST on the CBP and DCP is investigated. As a result, a loss of hydrophobicity occurred on the MPL surface. This altered the CBP and DCP, thus decreasing water management in the GDL.

The commonly used parameters characterizing fuel cells and in particular microbial fuel cells (MFCs) electrical performance are open circuit voltage (OCV), maximum power, and short circuit current. These characteristics are usually obtained from polarization and power curves. In the present study, the expanded uncertainties of operational characteristics for yeast-based fuel cell were evaluated and the main sources of uncertainty were determined. Two approaches were used: the uncertainty budget building for sources uncertainty estimation and a statistical treatment of identical MFCs results – for operational characteristics uncertainty calculation. It was found that in this particular bioelectrochemical system the major factor contributing to operational characteristics uncertainties was the electrodes' resistance. The operational characteristics uncertainties were decreased from 19 to 13% for OCV, from 42 to 14% for maximal power, and from 46 to 13% for short circuit current with the usage of electrodes with resistance in the interval 6–7 Ω. The described approaches can be used for operational characteristics expanded uncertainties calculation of all types of fuel cells using data from polarization measurements.

Proton exchange membrane fuel cell (PEMFC) is regarded as a potential future power technology for stationary and mobile applications due to its high efficiency (full and partial load), rapid start-up, high power density, and low emissions.

Depending on their particular application field (decentralized combined heat and power production, uninterrupted power supplies (UPS), or mobile applications) different operating conditions and designing parameters are required and different performance can be expected.

Thus, the aim of this paper is to investigate the behavior and performance of two stacks of the same size, developed with a different approach according to their application sectors.

The first PEMFC stack is designed for UPS units or mobile purpose, the second one, is designed to supply heat and power in residential applications (CHP units).

The analysis of the stacks behavior has been carried out by using both experimental and numerical investigations.

Experimental results have allowed: (i) to characterize the stacks; (ii) to calibrate the numerical model; (iii) to supply useful data for setting and improving the control system.

A model-based Design of Experiments method was employed for the optimization of measurements on a solid oxide fuel cell (SOFC). Based on a simplified SOFC model, a variation of the D-optimality was used as optimization criterion for the calculation of optimal experimental designs (determinant of the covariance matrix with weighting factors). Solutions for different numbers of design points were calculated and the behavior of optimization criteria as functions of the number of design points as well as of the number of repetitions of measurements was analyzed. A new type of graph was introduced which depicts the behavior of optimization criteria for constant number of measurements. This approach showed that, for constant numbers of measurements, the precision is higher and therefore the reliability in the cell's model identification is improved when repeated measurements of a small set of optimal design points are effectuated, instead of many different measurements. Finally, a sensitivity analysis was performed showing the influence of the parameter values on the values of the optimization criterion and the optimal measurements.

The used methodology and its theoretical conclusions may be used as a basis for development of diagnostics tools or filtering existing data for optimal parameter estimations.

The durability of polymer electrolyte membrane fuel cell with Pt catalysts supported on carbon nanotube (CNT) was investigated after a few hundred accelerated cell reversal process (RP) cycles generated by hydrogen deficiency. A variety of characterization techniques, including cell performance tests, were applied to examine the effects of CNT support on the degradation of Pt catalysts: transmission electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. During the RP cycle tests, most degradation by carbon corrosion occurred at the outlet region of membrane electrode assembly (MEA) where hydrogen starvation seriously occurred. By using the CNT as the support of Pt catalysts in the MEA cathode, carbon corrosion was reduced and growth of Pt particles by agglomeration and sintering significantly decreased. Compared to a commercial Pt/C catalyst, the cell durability of the Pt/CNT catalyst was enhanced under the RP condition.

When polymer electrolyte membrane materials are exposed to liquid water, they swell and distort. This frustrates the process of depositing liquid catalyst ink directly onto the membrane. We present a model predicting the transient compositional, thermal, and mechanical response of a membrane undergoing changes in water content. The model describes coupled heat and mass transfer and solid mechanics and is capable of describing the large changes in size and shape exhibited by a swelling membrane. Simulation results are presented for sorption and desorption and for the process of drying a saturated piece of membrane with an aqueous coating applied. We suggest that the well-established discrepancy in the rate of sorption and desorption may be partially due to pressure-driven diffusion effects absent in other models but present in ours. We also demonstrate that the model can represent the transient curling behavior of a membrane undergoing nonuniform changes in water content. The model will later be used to predict manufacturing defects caused by swelling-induced wrinkling.

This study focuses on the performances of proton exchange membrane fuel cells (PEMFCs) at 80 and 90 °C with feeds of varying degrees of humidification. The results show that ohmic resistance of the solid electrolyte decreases as the current density is raised because of the back diffusion of liquid water, that is, generated in the cathode active layer. On the other hand, severe liquid water accumulation occurs at high current densities, which hinders the oxygen transport in the cathode gas diffusion layer (GDL) resulting in the Nernst diffusion limitation. The polarization measurement correlates well with the electrochemical impedance spectroscopy (EIS) analysis. The effects of humidification on membrane hydration, activity in the catalyst layer, and oxygen diffusion over-potential in the cathode GDL are elucidated with the proposed equivalent circuit model at varying operating current densities.

Methanol crossover through polymer electrolyte membranes is a critical issue and causes an important reduction of performance in direct methanol fuel cells (DMFCs). Measuring the evolution of CO₂ gas in the cathode is a common method to determine the methanol crossover under real operating conditions, although an easier and simpler method is preferable for the screening of membranes during their step of development. In this sense, this work has been focused on the ex situ characterization of the methanol permeability in novel nanofiber-reinforced composite Nafion/PVA membranes for DMFC application by means of three different experimental procedures: (a) potentiometric method, (b) gas chromatography technique, and (c) measuring the density. It was found that all these methods resulted in comparable results and it was observed that the incorporation of the PVA nanofiber phase within the Nafion® matrix causes a remarkable reduction of the methanol permeability. The optimal choice of the most suitable technique depends on the accuracy expected for the methanol concentration, the availability of the required instrumental, and the complexity of the procedure.

Pd nanoparticles (NPs) with a mean size of 10–12 nm are dispersed on the surface of SiC nanowires (NWs) by a cyclic voltammetric deposition method, and employed as an electrocatalyst for methanol oxidation. The high dispersion and small size of supported Pd NPs enable the catalyst to have an electrochemical active surface area of 49.5 m² g^–1, which is larger than that of carbon nanotube supported Pd NPs (38.6 m² g^–1), and that of non-supported Pd NPs (29.9 m² g^–1). Methanol oxidation measurements show that the supported Pd NPs possess a high electrocatalytic activity and an excellent stability. These results indicate that SiC NWs have great potentials as an advantageous supporting material in alcohol fuel cells.

A hydrogen storage tank based on the metal hydride sodium alanate is coupled with a high temperature PEM fuel cell (HT-PEM). The waste heat of the fuel cell is used for desorbing hydrogen from the storage tank that in return feeds the fuel cell. ZBT has developed the HT-PEM fuel cell, Max-Planck-Institut für Kohlenforschung the sodium alanate, and IUTA the hydrogen storage tank. During the experiments of the system the fuel cell was operated by load cycling from 165 up to 240 W. Approximately 60 g of hydrogen were delivered from the tank, which was charged with 2676.8 g of sodium alanate doped with 4 mol.% of TiCl₃. This amount of hydrogen was desorbed in 3 h and generated a cumulated electrical energy of 660 Wh. In the first cycle 81.5 g of hydrogen were supplied during 3.69 h to the HT-PEM fuel cell, which was operated nearly constant at 260 W. In the latter case the cumulated electrical energy was 941 Wh.

Novel sulfonated copolymers bearing main chain pyridine units have been synthesized for use as electrolytes in high temperature proton exchange membrane fuel cells (PEMFCs). The aim was to combine the excellent thermomechanical properties and high conductivity values after doping with phosphoric acid of these materials with the ability of the sulfonic groups to absorb and retain water and finally to examine the effect on the proton conduction ability. The resulted copolymers showed excellent film forming properties, mechanical integrity, and high glass transition temperatures (T_g > 300 °C). The T_g of the sulfonated copolymers is strongly affected by the sulfonated group content in the polymer backbone due to the acid base interactions of the pyridine and sulfonated groups. Furthermore, the membranes exhibited remarkable oxidative stability and presented proton conductivities in the range of 10^–2 S cm^–1.