Assembly pressure compresses the under part of the gas diffusion layer, and the inhomogeneous compression can cause performance variation of the direct methanol fuel cell. Compared with the cell with traditional assembly method using bolts at the corner of plates, the cell with a novel assembly method uniforming the pressure is designed, fabricated, and tested in this paper. First, a three-dimensional model is developed to simulate the pressure distribution with different assembly patterns. Then, a multi-physics simulation including methanol mass transport, methanol diffusion, and electron transport is conduced. The modeling results reveal that the novel assembly method can ensure the flatness of the membrane electrode when compared with the traditional method. The overall performance first increases and then decreases with the increase of assembly pressure, and the optimal pressure is 1.5 MPa. Additionally, the cell with both assembly methods are fabricated and tested under optimal condition, and there are only <8% discrepancy between the experimental results and simulation; Influences of cell efficiency patterned with two assembly methods are also studied.

Understanding the current density distributions in polymer electrolyte fuel cells (PEFCs) is crucial for designing cell components, such as the flow field of bipolar plates. A new serpentine flow field equipped with sub-channels and by-passes (SFFSB) was numerically and experimentally confirmed to enhance the reactant transport rates and liquid removal efficiency compared with a conventional advanced serpentine flow field (CASFF). Consequently, the maximum current and the power densities of the SFFSB were increased due to the promotion of under-rib convection. In this study, current density distributions are measured under transient conditions to verify the PEFC performances enhanced by under-rib convection. The current density distributions of the SFFSB are compared with those of the CASFF. The results show that the SFFSB has a higher local current density and a more uniform distribution than the CASFF, therefore, the PEFC performances with the new flow field of SFFSB is enhanced by the better current density distributions.

Ultraporous Pd nanocrystals for electrocatalysis applications were fabricated using a direct electrodeposition method on three differing carbon supports: flexible carbon fiber paper (CFP), and CFP modified with either graphene oxide nanosheets or their chemically reduced forms using a simple spray coating technique. The electrocatalytic activity of these electrodes was investigated for the direct electro-oxidation reaction of methanol in alkaline media. Pd deposited on the CFP modified with reduced graphene oxide (rGO) has excellent poisoning tolerance to carbonaceous species and a significantly better catalytic activity toward methanol oxidation than the other two catalyst support materials. Pd/rGO/CFP in 2.0 M CH₃OH in 2.0 M NaOH yields a specific current density of 241 mAmg^–1 cm^–2 determined at the anodic oxidation peak. It is believed that the collaborative effects due to the three-dimensional ultraporous Pd nanocrystals and fast electron transfer owing to high conductivity of rGO nanosheets play an important role in enhancing the catalytic performance of Pd/rGO/CFP toward methanol oxidation in alkali media.

Degradation of carbon supported platinum catalysts is a major failure mode for the long term durability of high temperature proton exchange membrane fuel cells based on phosphoric acid doped polybenzimidazole membranes. With Vulcan carbon black as a reference, thermally treated carbon black and multi-walled carbon nanotubes were used as supports for electrode catalysts and evaluated in accelerated durability tests under potential cycling at 150 °C. Measurements of open circuit voltage, area specific resistance and hydrogen permeation through the membrane were carried out, indicating little contribution of the membrane degradation to the performance losses during the potential cycling tests. As the major mechanism of the fuel cell performance degradation, the electrochemical active area of the cathodic catalysts showed a steady decrease in the cyclic voltammetric measurements, which was also confirmed by the post TEM and XRD analysis. A strong dependence of the fuel cell performance degradation on the catalyst supports was observed. Graphitization of the carbon blacks improved the stability and catalyst durability though at the expense of a significant decrease in the specific surface area. Multi-walled carbon nanotubes as catalyst supports showed further significant improvement in the catalyst and fuel cell durability.

The characteristics of the measured total impedance spectra of polymer electrolyte membrane fuel cells are often not representative of the performance of the cell. This is due in part mainly to two reasons; total impedance measurements are not representative of local phenomena and perturbation of the cell around the steady-state polarization can result in oscillations of the gas concentrations downstream the flow channels that can affect the trend of the local spectrum. In this study, we overcome these two challenges by measuring the spectra of a segmented cell using local excitation of the segments. With these capabilities, we experimentally investigate the explanation given in works found in literature in regards to the oxygen oscillation in the channel and its effect on the spectra of locally perturbed segments. We further investigate the characteristics of the low frequency arc, measuring for the first time a loop in the spectrum around the transition frequency between the high and low frequency arcs. The characteristics of the spectra are investigated by varying the flow properties with a focus on the effect of air stoichiometry.

The direct formate fuel cell (DFFC) has recently been demonstrated as a viable alkaline direct liquid fuel cell (DLFC) that does not require addition of hydroxide to the fuel stream for operation. In this work, we report that the DFFC can produce significant power at low temperatures without added hydroxide, especially when compared with other alkaline DLFCs powered by alcohols. Using oxygen at the cathode, the DFFC powered by 1 M HCOOK achieves a maximum power density of 106 mW cm^–2 at 50 °C and 64 mW cm^–2 at 23 °C. Using air at the cathode, the same DFFC achieves a maximum power density of 76 mW cm^–2 at 50 °C and 27 mW cm^–2 at 23 °C. These power densities were achieved without addition of hydroxide to the fuel stream. Constant current operation demonstrates that the maximum power density can be maintained at least for several hours of operation. Finally, we use electrochemical analysis to demonstrate that the formate oxidation reaction is not dependent on pH between 9 and 14, which permits the use of formate fuel without added hydroxide in the DFFC. An alkaline DLFC that does not require added hydroxide is promising for safe and practical operation.

A residential photovoltaic (PV)-based hydrogen fuel cell (FC) system is analyzed using exergoeconomic methods, and its monthly performance is investigated. Mathematical models for predicting the power outputs of the PV and FC systems are presented. The results reported include the PV output and the shares attributable to the battery and the SOFC in supplying the electrical demand. Moreover, to study the performance of the hybrid system in supplying the daily demand, results are presented for two typical days in summer and winter. An exergoeconomic analysis is performed to determine the electricity unit cost over the system lifetime. The PV-electrolyzer system is not able to produce a sufficient amount of hydrogen during winter days, so seasonal hydrogen storage is required to feed the FC. Power penetrations of the PV and the battery systems are at maxima during the summer months, while the penetration of the FC system reaches 67% in January and December. Due to its low efficiency (16%), the maximum exergy destruction occurs in the PV modules (86%). The unit cost of electricity varies on a monthly basis, reaching a minimum of 0.26 $ kWh^–1 in July and a maximum of 1.8 $ kWh^–1 in January and December.

Mechanical properties of gadolinium-doped ceria (Ce_0.9Gd_0.1O_1.95, 10GDC) green tape prepared by aqueous-based tape casting process were characterized by tensile test and shear punch test (SPT). SPT was found to be a useful method for characterizing mechanical properties of green tapes. Microstructures and mechanical properties such as flexural modulus, bending strength, and microhardness of tapes sintered at 1,300–1,500 °C have been evaluated. Indentation fracture toughness was also determined by the method of Palmqvist cracks at different applied loads for tapes sintered at 1,500 °C. Grain size measurements showed that excessive grain growth occurred during sintering despite using 10GDC nanopowders as the starting material. However, mechanical properties of sintered tapes improved by increasing sintering temperature and the results are comparable with those reported for 10GDC in literature.

Furthermore, deposition at such low temperatures is promising for processing of thin film assemblies.

The preparation of bi-layer electrolytes of yttria stabilized zirconia and gadolinia doped ceria thin films by aerosol assisted chemical vapor deposition is demonstrated. Gadolinia doped ceria films as thin as 150 nm are applied as barrier layers between yttria stabilized zirconia electrolyte and La_0.6Sr_0.4CoO_3–δ cathode in anode supported solid oxide fuel cells. High power densities above 850 mW cm^–2 at 650 °C are only obtained with these barrier layers, indicating that the GDC thin films effectively inhibit the formation of unwanted interface reactions.

SrZr_0.84Y_0.16O_3–α (SZY16), BaZr_0.84Y_0.16O_3–α (BZY16), BaCe_0.8Zr_0.1Y_0.1O_3–α (BCZY10), and BaCe_0.90Y_0.10O_3–α (BCY10) thin films with the thickness of lower than 6 micron are successfully deposited by reactive magnetron sputtering on alumina substrate covered by about 200 nm Pt₃Ti collector layer. The corresponding ceramic bulk samples are prepared by solid state reaction. In order to obtain dense BZY16 and BCZY10 samples, 1 wt.% ZnO was added before sintering process.

As deposited films are amorphous and crystallise under the expected crystal structure at different temperatures (e.g., SZY16 ≈ 623 K; BZY16 ≈ 423 K; BCY10 ≈ 873 K, and BCZY10 ≈ 873 K). SZY16 and BZY16 coatings are stable in air with respect to carbonation and hydration. BZY16 coatings require an in situ crystallization in order to avoid further cracking due to the tensile stress generation associated with the crystallization phenomenon, so they are deposited directly onto hot substrate (T_substrate ≈ 523 K). BCZY10 amorphous coatings present a good chemical stability against carbonation in air up to 573 K but the coatings decompose in BaCO₃ and CeO₂ mixture after annealing treatment at around 873 K for 2 h in air, instead of the expected double substituted BaCeO₃ perovskite structure. Nevertheless, the crystallization perovskite structure is obtained after annealing treatment under vacuum to prevent the carbonation of the coating. BCY10 requires in situ crystallisation (T_substrate ≈ 873 K) to obtain BaCeO₃ structure while avoiding the carbonation of the film. All the bulk samples present the perovskite structure with a relative density higher than ∼80% and without trace of ZnO or BaCO₃. Eighty percent of relative density was demonstrated to give a good compromise between porosity and grain boundary blocking effects. The electrical properties of the films and pellets are investigated by AC impedance spectroscopy in air. Conductivities of crystallised coatings are close but always significantly lower than those of ceramic bulk samples of the same composition.

In this report, we describe fabrication and electrochemical-performance testing of tubular, anode-supported fuel cells based on the protonic ceramic BaCe_0.2Zr_0.7Y_0.1O_3–δ (BCZY27). These devices are comprised of a 20-μm-thick BCZY27 electrolyte spray-coated and co-fired onto an extruded, tubular 9.8-mm-diameter, 1.25-mm-thick 65 wt.% NiO/35 wt.% BCZY27 anode support. Reactive sintering with NiO forms the BCZY27 material from parent oxides. An La_0.6Sr_0.4 Co_0.2Fe_0.8O_3–δ (LSCF) cathode is applied following co-sintering. While anode supports can be extruded to 3-m lengths, the active area of the cells tested here is 7.5 cm². Performance is quantified through polarization measurements across a range of temperatures with hydrogen-air reactants. Peak power ranges from 78 to 189 mW cm^–2 over the 700–850 °C temperature range. Open-circuit voltage decreases with increasing operating temperature due to the co-diffusion of the multiple charge carriers present. The ionic transference number is determined over a range operating temperatures and anode-gas compositions, and is found to range from 0.77 to 0.88. Finally, an external power supply is used to drive hydrogen across the BCZY27 membrane. At an applied current density of 1 A cm^–2 and 700 °C operating temperature, hydrogen flux is measured at 7.5 smL min^–1 cm^–2 active area.

High temperature steam electrolysis (HTSE) is one of the most promising ways for hydrogen mass production. If coupled to a CO₂-free electricity and a low cost heat source, this process is liable to a high efficiency. High levels of performance and durability, in association with cost-effective stack and system components are the key points. To reach such goals, a low-weight stack has been designed, keeping the advantages of the high performing and robust stack previously validated in terms of performance, durability, and cyclability [1], but aiming at reducing the cost by the use of thin interconnects. This low-weight stack has demonstrated at the scale of a 3-cell stack a good performance of –1.0 A cm^–2 at 1.3 V at 800 °C. Before performing the durability test, preliminary studies at the cell level have been carried out to highlight the effect of two major operating parameters that are the current density and the steam conversion (SC) ratio, those studies being carried out at one temperature, 800 °C. Based on these results, optimized operating parameters have been defined to perform the durability test on the stack, that is –0.5 A cm^–2 and a SC ratio of 25%. Degradation rates around 3–4% 1,000 h^–1 have been measured. The thermal cyclability of this stack has also been demonstrated with one thermal cycle. Therefore it can be concluded that these results make HTSE technology getting closer to the objectives of performance, durability, thermal cyclability, and cost.

In this work, co-electrolysis of steam and carbon dioxide was studied in a Topsoe Fuel Cell (TOFC®) 10-cell stack, containing three different types of Ni/yttria stabilized zirconia (YSZ) electrode supported solid oxide electrolysis cells with a footprint of 12 × 12 cm. The stack was operated at 800 °C and –0.75 A cm^–2 with 60% conversion for a period of 1,000 h. One type of the cells showed no long term degradation but actually activation during the entire electrolysis period, while the other two types degraded. The performance and durability of the different cell types is discussed with respect to cell material composition and microstructure. The results of this study show that long term electrolysis is feasible without notable degradation at 800 °C and a current density of –0.75 A cm^–2.

As solid oxide fuel cell (SOFC) technology is moving closer to a commercial break through, lifetime limiting factors, and methods to measure the “state-of-health” of operating cells and stacks are becoming of increasing interest. This requires application of advanced methods for detailed electrochemical characterization during operation.

An experimental stack with low ohmic resistance from Topsoe Fuel Cell A/S was characterized in detail using electrochemical impedance spectroscopy (EIS). An investigation of the optimal geometrical placement of the current feeds and voltage probes was carried out in order to minimize measurement errors caused by stray impedances. Three different stack geometries were investigated by impedance spectroscopy and the stack geometry with the minimum effect of stray impedances was selected.

A 13-cell experimental SOFC stack was tested during 2,500 h of operation with hydrogen as fuel with 52% fuel utilization and constant current load (0.2 A cm^–2) at 750 °C. Stack interconnects were coated with six different coatings to prevent chromium poisoning on the cathode side. Four repeating units (RUs) with different coatings were selected for detailed impedance analysis. EIS allowed a distinction to be made in terms of the degradation between the four RU types that is not possible from IV-data only.

This paper describes 3D tomographic investigations of the structural evolution of Ni-yttria-stabilized zirconia (Ni-YSZ) and (La,Sr)MnO₃-YSZ (LSM-YSZ) composite solid oxide fuel cell (SOFC) electrodes. Temperatures higher than normally used in SOFC operation are utilized to accelerate electrode evolution. Quantitative 3D FIB-SEM and X-ray tomographic imaging contributes to development of mechanistic evolution models needed to accurately predict long-term durability. Ni-YSZ anode functional layers annealed in humidified hydrogen at 900–1,100 °C exhibited microstructural coarsening leading to a decrease in three-phase boundary (TPB) density. There was also a change in the fraction of pores that were isolated, which impacted the density of electrochemically active TPBs. The polarization resistance of optimally fired LSM-YSZ electrodes increased upon thermal aging at 1,000 °C, whereas that of under-fired electrodes decreased upon aging. These results are explained in terms of observed 3D microstructural changes.

Elastic properties and residual stresses are critical for the assessment of the reliability of ceramics components. The thin electrolyte layer of anode supported SOFCs is under a state of high compressive residual stress. In the present study, the elastic properties of this layer as well as the residual stress distribution induced in the anode-supported planar SOFC cell were examined by using the resonant ultrasound spectroscopy (RUS). A modal analysis by finite element simulation demonstrated that the RUS has a great potential to determine these mechanical characteristics. The Young's modulus can be determined from the natural frequencies of the layered sample whilst the residual stress can be determined using the sample with a semi-hole. Estimates of the Poisson's ratio are possible. In the experiment, various individual resonant oscillations were successfully identified using the present RUS system. Hence, by comparison of experimental results and simulations, the elastic properties as well as the residual stress were obtained. Although the proposed method is still experimentally challenging, it could be developed to become a powerful tool to simultaneously determine residual stresses and elastic constants of thin-layered systems.

The present study is focused on alternative structured oxygen electrodes for solid oxide electrolysis cells (SOEC). The Ln₂NiO_4+δ (Ln = La or Pr) nickelate oxides were selected as innovative electrode materials with respect to their mixed electronic and ionic conductivity. A thin interfacial ceria-based layer was added in between the electrode and the zirconia-based electrolyte to improve mechanical and electrochemical properties and to limit the chemical reactivity. These structured cells were characterized by electrochemical impedance spectroscopy on symmetrical cells, under zero dc conditions and anodic polarization. Low polarization resistance R_P and improved anodic overpotential η_A versus current density curves were obtained for the Pr₂NiO_4+δ electrode with Ce_0.8Y_0.2O_2–δ interlayer: R_P is decreased down to 0.06 Ω cm² at 800 °C, under air and zero dc conditions. Then, complete hydrogen electrode-supported cells including Pr₂NiO_4+δ as oxygen electrode were electrochemically characterized. At 800 °C, when the inlet gas composition is 90 vol.% H₂O–10 vol.% H₂ at the hydrogen electrode, air being swept at the oxygen electrode, the current density determined at 1.28 V reaches –0.9 A cm^–2, the corresponding steam to hydrogen conversion ratio being 58%. These results are compared to those obtained with a reference cell including the oxygen deficient perovskite La_0.6Sr_0.4Fe_0.8Co_0.2O_3–δ as oxygen electrode.

The glass–ceramic sealants developed at Forschungszentrum Juelich already meet several of the requirements for their potential use in SOFC stacks. The adequate choice of glass materials and adaptation of the joining and design parameters are essential for stack assembling. Successful long time operation of stacks depends on sufficiently high bond strength between sealant and other components. Currently one of the major problems has been to find a glass–ceramic sealant with appropriate strength withstanding operation conditions. Therefore a reinforcement concept was developed based on addition of silver particles, YSZ fibers or particles as fillers in glass matrix from the system BaO–CaO–SiO₂. Additionally different screen-printed laminar combinations were prepared as double and triple layer design. The double layer design consists in one with ceramic filler and another one with metal filler addition. Triple layer design was set up by establishing two identical films on the outer sides and one different reinforcement layer in the center plane. In order to evaluate the multilayer designs' strength, tensile tests were carried out on circular butt-joints. The three layers combination showed best performance. Samples could be qualitatively compared in a relative ranking. Changes in the tensile test configuration were proposed to improve future evaluation.

Sulfur poisoning behavior of La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF6428) cathode was investigated at T = 1073 K (800 °C) under 0.1 ppm of SO₂-air mixture gas; the amount of supplied SO₂ was controlled by changing the flow rate. Two stages of the performance degradation were found: a rapid degradation at the early stage and a subsequent monotonic degradation. The elemental distributions of SrSO₄ showed a strong correlation between the electrochemically active sites and SrSO₄ reaction sites in the vicinity of the LSCF6428/10GDC interfaces. Considerations were made to attribute the first and the second stages of performance degradation to the SO₂ adsorption and the SrSO₄ formation, respectively. The SO₂ adsorption mechanism was discussed in terms of the high concentration of oxide ion vacancies in the electrochemically active region under the cathodic polarization condition.

The key-requirements for glass ceramic sealing materials to achieve high efficiencies in planar solid oxide fuel cells are leak tightness, high insulating resistance, and low reactivity in contact with the anode or cathode gases and the interconnect material. Therefore SCHOTT has developed special glasses and glass-ceramics for chromium alloys, like Cr5FeY (CFY, Plansee SE). Especially the CFY material requires adapted sealing materials due to its lower coefficient of thermal expansion (CTE) compared to ferritic stainless steels and the possibility for interface reactions originating from the high chromium content and the glass seal components. In this study, new glass-ceramic sealing materials for chromium containing alloys are presented. Results show that barium-free glass-ceramics are advantageous when sealing high chromium alloys in terms of interface reactions. Because of the absence of barium oxide, formation of detrimental chromate phases at the interface was avoided. The new glasses show low porosity, high hermeticity, and strong bonding toward the CFY material, fulfilling the requirements of SOFC sealants.

The increasing interest in lightweight solid oxide fuel cell (SOFC) systems for mobile applications has raised the awareness for questions concerning mechanical robustness of sealing materials in thermo-cyclic operation. In the planar SOFC design considered in the current work, a metallic silver based braze sealant is used. Although, these rather ductile metallic seals are considered to have advantages compared to brittle glass ceramics under thermal cycling conditions, the behavior of such sealant materials after application relevant thermal cyclic operation has not been reported so far. Hence, the post-operational characterization of a series of silver braze sealed stacks operated isothermally and under thermal cycling conditions is reported with particular emphasis on the braze morphology. The stacks were disassembled after operation, specimens were extracted in various characteristic positions, and metallographically prepared cross-sections were analyzed by optical and electron microscopy. It was observed that micro-pores were formed in the sealant that terminated stack operation, and that the extent of this porosity depended on the actual operation conditions leading eventually to leakage and in some cases even to melting effects. The discussion of the results focuses on the influence of different operation conditions on the damage progress and failure of silver based braze joints.

Recent progress of the NEDO project on durability/reliability of SOFC stacks is reported with an emphasis on the achievement of Mitsubishi Heavy Industries' segment-in-series cells in which the lanthanum manganite cathode has been improved. Durability tests were made by CRIEPI on their cells with/without doped ceria interlayer to check plausible effects of microstructure change and of chromium poisoning. Improved cells exhibit essentially no degradation for 10,000 h and also strong tolerance against the Cr contamination from stainless steel tubes. These features are discussed within the generalized degradation model developed inside the NEDO project. In particular, the extremely small overpotential can be considered to be effective in lowering the Cr poisoning by reducing the driving forces for the electrochemical Cr deposition at active sites. Insertion of doped ceria is also useful in preventing the Cr deposition or enhancing the volatilization of deposited Cr with cathodically emitted water vapors from ceria. Thermodynamic considerations reveal that the initial composition of LSM cathode is important to determine the microstructure change due to the chromium dissolution into the B-sites in the perovskite lattice. Discussions are made on a role of doped ceria to prevent deterioration of Mn-dissolved electrolyte by lowering the Mn dissolution into YSZ.

A detailed electrochemical impedance study with the help of the distribution of relaxation times (DRT) method and a subsequent CNLS-fit enabled us to quantitatively analyze the different loss contributions in the cell: the ohmic resistance and the polarization processes related to the gas diffusion in the metal support, the electrochemical fuel oxidation at the anode and the oxygen reduction in the mixed ionic electronic conducting cathode. An additional process with a rather high relaxation frequency was attributed to the formation of insulating interlayers at the cathode/electrolyte-interface. Based on these results, selective measures to improve performance and stability, such as (i) PVD-deposited CGO buffer layer preventing solid state reaction between cathode and the zirconia-based electrolyte, (ii) LSC-CGO based in-situ sintered cathodes and (iii) reduced corrosion of the metal support, were adopted and validated.

The impact of sulfur-poisoning on reforming chemistry and electrochemistry of anode-supported solid oxide fuel cells is analyzed via electrochemical impedance spectroscopy. Different types of anode supported cells are operated in hydrogen/steam – as well as simulated reformate – (H₂ + H₂O + CO + CO₂ + N₂) fuels containing 0.1–15 ppm of H₂S. A detailed analysis of impedance spectra by the distribution of relaxation times (DRT) and a subsequent complex nonlinear least squares (CLNS) fit separates the impedance changes taking place at the anode and the cathode. Two main features were detected in the DRT, a decreased reaction rate of the electrochemical hydrogen oxidation and a deactivation of the catalytic conversion of CO via the water-gas shift reaction. During the first exposure of the cell to a H₂S-containing fuel, an enhanced degradation is observed. The degradation rate increases several hours after H₂S was added to the fuel and decreases after the poisoning is completed. The polarization resistance increased by a factor of 2–10, depending on H₂S-content, fuel composition and cell type. Comparing the temporal characteristics of the polarization resistance of two different anode supported cells, it could be shown that the accumulated H₂S-amount divided by the Ni-surface area inside the anode substrate and anode functional layer determine the onset of the degradation.

In this work we investigate the effect of Cr-poisoning at OCV-condition by means of electrochemical impedance spectroscopy (EIS). The anode-supported cell (ASC) is operated in Cr-free environment for the first 70 h of the cell test at 800 °C supplying air to the cathode and a varying mixture of H₂O/H₂ to the anode. The performance of the cell is determined by current-voltage (CV) measurement after the start up. After an operating time of 70 h in the absence of chromium species a Cr-source was switched on by passing the oxidant (air) through a Crofer22APU powder bed. In order to determine the degradation caused by Cr-poisoning electrical impedance spectra are collected at every 29 h of operating time. After further 275 h at OCV-condition in the presence of Cr-source another CV-curve is measured. A detailed analysis of the measured impedance spectra by the distribution of relaxation times (DRT) enables a separation of the cathode polarization resistance. During the Cr-free operation the cathode polarization shows a constant value. After the Cr-source is switched on a strong increase of the cathode polarization resistance is observed. This unique result shows clearly that Cr-poisoning of an LSM/8YSZ-cathode already takes place at OCV-condition.

The concept of using electronically conducting anode backbones with subsequent infiltration of electrocatalytic active materials has been used to develop an alternative solid oxide fuel cell (SOFC) design based on a ferritic stainless steel support. The anode backbone consists of a composite made of Nb-doped SrTiO₃ (STN) and FeCr stainless steel. A number of different experimental routes and analysis techniques have been used to evaluate the microstructural and chemical changes occurring in the composite anode layer during electrochemical testing at intermediate temperatures (650 °C). STN and FeCr stainless steel was found to be compatible on the macro-scale level, however, some micro-scale chemical interaction was observed. The composite anode backbone showed a promising corrosion resistance, with a decrease in formation of Cr₂O₃ on the FeCr particles, when exposed to SOFC operating conditions. The electronic conductivity of the infiltrated anode backbone furthermore showed good redox stability properties. Electrochemical testing of metal-supported cells having the STN:FeCr composite anode backbone infiltrated with electrocatalysts showed comparable performance and promising durability properties compared with other metal-supported cell designs presented in the literature. This work illustrates the potential advantages and challenges when incorporating SrTiO₃-based materials into metal-supported cells based on ferritic stainless steel.

Forschungszentrum Jülich is performing long-term SOFC stack tests for more than 17 years. Within the European project Real-SOFC (2004–2008) durability tests operating at 700 °C were started with two short stacks which reached the first milestone of 10,000 h in November 2008. The operation of one stack, clearly showing progressive degradation over the last 5,000 h, was terminated after more than 2 years for inspection of the status of the components and interfaces. The second stack is now in operation for more than 5 years having reached 43,800 h in August 2012. The average voltage degradation over the full duration was about 1% per 1,000 h. Another short stack with plasma sprayed protective coatings on the air side of the interconnects is running for more than 14,000 h, showing about 0.12% voltage degradation per 1,000 h. A stack with a similar configuration but LSM cathodes, operated at a temperature of 800 °C, broke down after 2 years. As reason for the break-down manganese diffusion from the LSM cathode into the 8YSZ electrolyte could be determined by post-test analysis. All these short stacks have been tested with humidified hydrogen at a fuel utilization of 40% and with dry air. In the meantime a 2.6 kW stack was operated on internally reformed methane for 4,500 h showing about 0.3% voltage degradation per 1,000 h.

This investigation is performed to study the optimal operation decision of two-chamber microbial fuel cell (MFC) system under uncertainty. To gain insight into the mechanism of uncertainty propagation, a Quasi-Monte Carlo method-based stochastic analysis is conducted not only to elucidate the effect of each uncertain parameter on the variability of power density output, but also to illustrate the interactive effects of the all uncertain parameters on the performance of MFC. Moreover, a systematic stochastic simulation-based multi-objective genetic algorithm framework is proposed to identify a set of Pareto-optimal robust operation strategies, which is helpful to provide an imperative insight into the relationship between the mean and standard deviation of output power density. The results indicate that (1) the coefficient of variance (COV) value of output power density has a linear relationship with the COV value of each uncertainty parameter as well as all interactive parameters; and (2) a significant performance improvement with respect to both mean and standard deviation of power density is observed by implementing the multi-objective robust optimization. These results thus validate that the proposed uncertainty analysis and robust optimization framework provide a promising tool for robust optimal design and operation of fuel cell systems under uncertainty.

In this work, a microfabricated anode based on gold coated poly(ϵ-caprolactone) fiber was developed that outperformed gold microelectrode by a factor of 2.65-fold and even carbon paper by 1.39-fold. This is a result of its ability to three-dimensionally interface with bacterial biofilm, the metabolic “engines” of the microbial fuel cell (MFC). We also examined unavoidable issues as the MFC is significantly reduced in size (e.g. to the microscale); (1) bubble production or movement into the microchamber and (2) high sensitivity to flow rate variations. In fact, intentionally induced bubble generation in the anodic chamber reduced the MFC current density by 33% and the MFC required 4 days to recover its initial performance. Under different flow rates in the anode chamber, the current densities were almost constant, however, the current increased up to 38% with increasing flow rate in the cathode.

Multi-step synthetic pathways to low-ion exchange capacity (IEC) polysulfone (PSU) with sulfonic acid functionalized aliphatic dendrons and sulfonated comb-type PSU structures are developed and investigated in a comparative study as non-fluorinated proton exchange membrane (PEM) candidates. In each case the side chains are synthesized and introduced in their sulfonated form onto an azide-functionalized PSU via click chemistry. Three degrees of substitution of each architecture were prepared in order to evaluate the dependence on number of sulfonated side chains. Solution cast membranes were evaluated as PEMs for use in fuel cells by proton conductivity measurements, and in the case of dendronized architectures: thermal stability. The proposed synthetic strategy facilitates exploration of a non-fluorous system with various flexible side chains where IEC is tunable by the degree of substitution.

The graphene was synthesized by chemical oxidation followed by thermal exfoliation of natural graphite. The functionalized graphene (FG) was prepared by chemical treatment of the synthesized graphene. The as-synthesized graphene and FG were characterized and used as Pt support materials. The 20 wt.% Pt/G and 20 wt.% Pt/FG catalysts were prepared by precipitation method. The prepared catalysts were characterized for particle size using X-ray diffraction, surface morphology, electrochemical performance, and stability using cyclic voltammetry. The electrochemical surface area of the FG supported platinum catalyst was found to be more than 45% as compared to the commercial carbon supported platinum catalyst. The stability of the developed catalyst (Pt/G and Pt/FG) was significantly higher than the commercial Pt/C. The membrane electrode assembly was developed using the catalysts and tested in a PEMFC. The maximum power densities of the fuel cell were found to be 314, 426, and 455 mW cm^–2 using Pt/C, Pt/G, and Pt/FG, respectively.

An efficient method was developed to produce highly dispersed Pd nano particles (NPs), supported on Nafion-graphene film by electrochemical deposition at constant potential in presence of ferrous ions. The Fe²⁺ ions govern the size, shape and morphology of Pd NPs. The as-prepared catalyst was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). It was obeserved from TEM that the mean diameter of electrodeposited Pd NPs was 6.4 ± 1.3 nm with narrow diameter range from 4 to 10 nm. The electrocatalytic performance of the Pd NPs deposited on Nafion-graphene (Nf-G) catalyst was studied by cyclic voltametry (CV) and chronoamperometric measurements. The highly dispersed Pd NPs on Nf-G film were obtained in presence of Fe²⁺ ions. This alters electrochemical active surface area and hence catalytic activity of Pd NPs. The prepared Pd/Nf-G catalyst exhibit highest tolerance to the intermediate poisoning species (ratio I_f/I_b = 2.2). The as-obtained catalyst shows an efficient electrocatalytic activity and good stability for ethanol oxidation in alkaline medium.

Water evolution, distribution, and removal in the cathodes of a running direct methanol fuel cell were investigated by means of synchrotron X-ray radiography. Radiographs with a spatial resolution of around 5 μm were taken every 5 s. Special cell designs allowing for through-plane and in-plane viewing were developed, featuring two mirror-symmetrical flow field structures consisting of one channel with the through-plane design. Evolution and discharge of water droplets and the occurrence of water accumulations in selected regions of the channels were investigated. These measurements revealed a nonuniform distribution of water in the channels. Both irregular and periodic formation of water droplets were observed. In-plane measurements revealed, that the droplets evolve between adjacent carbon fiber bundles of the gas diffusion layer. The water distribution within the channel cross-section fits very well to the pressure difference between cathode channel inlet and outlet. The quick discharge of water droplets causes sudden decreases of the pressure difference up to 4.5 mbar.

A novel PtPd/C nanowire catalyst with interconnected network and fewer great grain boundaries has been successfully prepared by templateless and modified phase-transfer method using cetyltrimethylammonium bromide as a capping in ethylene glycol solution by microwave-assisted process. Its structure, composition, and morphology are characterized by X-ray diffraction, energy dispersive analysis of X-ray, and transmission electron microscopy, respectively. The electrochemical measurements demonstrate that the highly dispersed and uniform PtPd/C nanowire networks catalyst has a significantly higher electrocatalytic activity and durability for the methanol oxidation as compared to solid solution PtPd/C. The greatly improved durability of PtPd/C nanowire networks catalyst is mainly a consequence of the unique interconnected network structure with fewer grain boundaries, which provide more facile pathway for the electron transfer, and inhibit the particle growth and agglomeration, as well as prevent the particles embedded in the microporous of carbon support to enhance the Pt utilization.

Carbon-encapsulated cobalt-tungsten carbides (CoWC@C) were synthesized by reduction and carbonization method and used as the electrocatalyst for oxygen reduction reaction (ORR) in direct methanol fuel cells. The as-prepared samples were characterized by transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy. The results show that CoWC@C consists of outer layer carbon and internal Co₃W₃C, WC, and Co. The cyclic voltammetry results show that CoWC@C has high ORR activity, long-term durability, and good methanol-tolerant performance. It is revealed that the main active phase for ORR of CoWC@C is Co₃W₃C, and the outer layer carbon plays the role in improving the durability of the catalyst.

We developed novel Ag–glass composite interconnect materials for anode-supported flat-tubular solid oxide fuel cells (SOFCs) operated at 700 °C by optimization of the glass content. For this purpose, the variations of phase stability, area specific resistance (ASR), microstructure, gas leak rate, cell performance, and open circuit voltage (OCV) were determined for the Ag–glass composite materials with respect to the glass content. The Ag–glass composite materials maintain phase stability without chemical reactions. The ASR increased as the glass content increases due to glass existing as an insulator between the Ag phases. All the composite materials showed dense coating layers on the anode support and had a low gas leak. The cell performance and OCV were measured to identify the optimum composition of the Ag–glass composites. Our results confirm that Ag–glass composites are suitable for high performance interconnects in anode-supported flat-tubular fuel cells operated below 700 °C.

In order to simulate the contact situation of interconnect/contact layer/cathode in SOFC stacks, contact resistance and chemical compatibility of LaNi_0.6Co_0.4O_3–δ (LNC) as contact layer between Crofer22APU interconnect and La_0.6Sr_0.4FeO₃ (LSF) cathode was investigated at 800 °C in air for more than 1300 h using X-ray diffraction (XRD), scanning electron microscopy (SEM) set-up equipped with an energy dispersive X-ray analyser (EDX) and area specific resistance (ASR) measurements. The XRD analysis reveals that multiple phases were formed during ASR test. The point microanalysis on cross-section of Fe–Cr/LNC/LSF system, after ASR measurements, shows chromium within the porous contact material mainly concentrated close to interconnect, but no Cr, Ni, or Co was detected in the cathode. It was found between LNC and LSF cathode, a thin and uniform layer which contains Sr, La, Cr, Co, Ni, and Fe. The contact between layers could act as a physical barrier for element migration and thus can suppress degradation of the cathode for these systems. The area specific resistance slope depends on the interactions between the contact material and/or cathode and the interconnect. Co-containing spinels formed during ASR test can be responsible of the resistance decrease of the system, related to the low degradation of the cell.

To increase the long term stability and performance of solid oxide fuel cell (SOFC) materials, it is important to understand the main degradation processes in their functional layers. In this work, the interface between electrolyte and anode material was investigated by in situ X-ray diffraction (XRD) stress and phase analysis. It has been found that the determining process for the initial degradation of SOFC is the reduction of the anode material with hydrogen. During this process a tensile strength of 600–700 MPa is measured. These stresses are induced in the electrolyte material and produce crack networks. The reduction from nickel oxide to pure nickel was monitored by in situ phase analysis. This reaction induces tensile stress at the interface between electrolyte and anode. The stress produced in the electrolyte material was also confirmed by the observation of crack networks detected using scanning electron microscopy (SEM). Finally, the reducing process was optimized using different process gases, decreasing the destructive tensile stress level.

The fuel flexibility of solid oxide fuel cells (SOFCs) is one of the advantages of this technology, and biosyngas produced from biomass is emerging as a new fuel. The fuelling of SOFCs with different fuels is always challenging because of the associated risks. Mathematical modeling tools are useful for predicting the operational safety constraints and designs of SOFCs that are suitable for different fuels. Using a single channel model that incorporates direct internal reforming (DIR), this work investigates the fuel flexibility of an anode-supported intermediate temperature planar solid oxide fuel under co-flow operation. The DIR reaction of methane, the water-gas shift reaction (WGS) and the electrochemical reaction of hydrogen are the three reactions taken into account in this simulation work. Detailed comparisons of the gas concentrations, the current density distributions and the temperature change profiles are presented and discussed. These simulation results provide the initial data for performance analyses and safety predictions, which will be helpful for our future experimental investigations. The thermodynamic predictions of both nickel oxidation and carbon deposition are employed to check the operational safety of SOFCs fuelled with biosyngas.

The nickel-based anodes of solid oxide fuel cells (SOFCs) can catalytically reform hydrocarbons, which make natural gas, gasification syngas, etc., become potential fuels in addition to hydrogen. SR and water–gas shift (WGS) often occur inside SOFCs when operated on these fuels. Their reaction rates affect the partial pressures of hydrogen and carbon monoxide, the local temperatures and the related Nernst voltages. Consequently, the reaction rates affect the electrochemical reactions in the fuel cell. Three different kinetic models were used to characterize methane SR in a tubular SOFC; the results of each model were evaluated and compared. The polarizations of the fuel cell results of these models were validated against experimental data. The performance of a fuel cell operated with different fuels and based on a selected kinetic model was further studied in terms of the anode oxygen partial pressure, the thermo-electrochemical distribution, and the system level performance.

Thin cathodes for micro-solid oxide fuel cells (micro-SOFCs) are fabricated by spin-coating a suspension of La_0.6Sr_0.4CoO_3–δ (LSC) nanoparticulates obtained by salt-assisted spray pyrolysis. The resulting 250 nm thin LSC layers exhibit a three-dimensional porous microstructure with a grain size of around 45 nm and can be integrated onto free-standing 3 mol.% yttria-stabilized-zirconia (3YSZ) electrolyte membranes with high survival rates. Weakly buckled micro-SOFC membranes enable a homogeneous distribution of the LSC dispersion on the electrolyte, whereas the steep slopes of strongly buckled membranes do not allow for a perfect LSC coverage. A micro-SOFC membrane consisting of an LSC cathode on a weakly buckled 3YSZ electrolyte and a sputtered Pt anode has an open-circuit voltage of 1.05 V and delivers a maximum power density of 12 mW cm^–2 at 500 °C.