A metal-supported solid oxide fuel cell (SOFC) using Ce0.8Sm0.2O2 (Sm-doped ceria, SDC) buffer layer and La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte films showed a small degradation in the cell performance after a long-term operation because of La migration from the electrolyte to the buffer layer, resulted in a formation of a less conductive phase. Thus, various ceramic materials such as doped ceria and perovskite-related oxides were investigated for an effective buffer layer with respect to fabricating reliable metal-supported SOFCs using a LSGM electrolyte film. In particular, La-doped CeO2 (LDC) and Pr-doped LaCrO3 (LPCr) were investigated as buffer layer material since the materials showed chemical compatibility with the LSGM and anode materials. The cell using a LDC buffer layer showed a prior stability during the operation for 100 h at 973 K, while the power density of the cell was slightly low owing to the low electrical conductivity of LDC compared with that of SDC or LPCr. In contrast, the cell using a LPCr buffer layer revealed significantly low open circuit voltage (OCV) and power density, which were attributed to Pr decomposition in the LPCr caused by the reactivity with water vapor. However, the metal-supported cell with a multilayer electrolyte film including LSGM/LPCr/SDC layers showed an almost theoretical OCV and reasonably high power density with no degradation after a long-term operation for 100 h at 973 K, suggesting that the LPCr layer effectively prevented La migration and the SDC layer led to avoid the Pr decomposition. Thus, a LPCr is an effective buffer layer material for reliable metal-supported SOFCs using a LSGM electrolyte thin film.

The thermodynamic La–Sr–Mn–Cr–O oxide database is obtained as an extension of thermodynamic descriptions of oxide subsystems using the calculation of phase diagrams approach. Concepts of the thermodynamic modeling of solid oxide phases are discussed. Gibbs energy functions of SrCrO4, Sr2.67Cr2O8, Sr2CrO4, and SrCr2O4 are presented, and thermodynamic model parameters of La–Sr–Mn–Chromite perovskite are given. Experimental solid solubilities and nonstoichiometries in La1−xSrxCrO3−δ and LaMn1−xCrxO3−δ are reproduced by the model. The presented oxide database can be used for applied computational thermodynamics of traditional lanthanum manganite cathode with Cr-impurities. It represents the fundament for extensions to higher orders, aiming on thermodynamic calculations in noble symmetric solid oxide fuel cells.

We have used molecular dynamics simulations to examine membrane morphology and the transport of water, methanol, and hydronium in phenylated sulfonated poly(ether ether ketone ketone) (Ph-SPEEKK) and Nafion membranes at 360 K for a range of hydration levels. In Ph-SPEEKK, the average pore diameter is smaller, the sulfonate groups are more closely packed, the hydronium ions are more strongly bound to sulfonate groups, and the diffusion of water and hydronium is slower relative to the corresponding properties in Nafion at comparable hydration levels. The aromatic carbon backbone of Ph-SPEEKK is more rigid and less hydrophobic than the fluorocarbon backbone of Nafion. Water network percolation in Ph-SPEEKK occurs at a hydration level (λ) of ∼8 H2O/SO3−. At λ = 20, water, methanol, and hydronium diffusion coefficients were 1.4 × 10−5, 0.6 × 10−5, and 0.2 × 10−5 cm2/s, respectively. For λ > 20, wide pores develop leading to an increase in methanol crossover and ion transport.

The proton conducting perovskite MZr1−xLnxO3−δHz ceramics are promising electrolytic membranes for fuel cell and water steam electrolyser applications. Simultaneous elastic/quasielastic and diffraction neutron studies were performed in a wide temperature range (25–1150 °C) on protonated Yb-modified BaZrO3 ceramics: dense (97% of theoretical density) and ultradense (99%) using the triple axis spectrometers. The results allowed us to determine: (i) the real content of bulk protonic species ∼1–5 10−3 mol/mol, (ii) the structural modifications caused by the proton doping, and (iii) the bulk proton dynamics. The quasielastic neutron scattering (QNS) results are discussed in the light of neutron diffraction, conductivity, Raman, thermogravimetric, and thermal expansion measurements. The highest bulk proton motion appears in the temperature range where the structural modifications and the energy activation changes are detected. This allows defining the optimum temperature range for the proton dynamics between 400 and 560 °C.

The thermal and mechanical behavior, the water uptake (WU), and water diffusion coefficient of sulfonated poly(ether ether ketone) (SPEEK) membranes annealed at 180 °C for different times were explored by high-resolution thermogravimetric analysis, mechanical tensile tests, dynamic mechanical analysis, and WU measurements. The mechanical and thermal stability increased with the thermal treatment time, i.e., with the degree of crosslinking. The effect of residual casting solvent, dimethyl sulfoxide (DMSO), on the WU within SPEEK was probed. In presence of residual DMSO, crosslinked SPEEK exhibited higher water sorption at low and medium relative humidity (RH), and lower water sorption at high RH. These membranes have properties well adapted to fuel cell applications.

Phosphonated polysulfones in the acid form (PPSU-As) with degree of phosphonation (DP) = 0.4, 0.75, and 0.96 were successfully synthesized and utilized for the preparation of polymer blend with sulfonated poly(ether ether ketone) (SPEEK) having a degree of sulfonation (DS) = 75. The resulted blend membranes were characterized and investigated as new polyelectrolyte membrane for fuel cells applications. SPEEK/PPSU-A blend membranes formed ionic networks through hydrogen bonding bridges between the strong sulfonic acid groups and the amphoteric phosphonic acid groups. These ionic interactions resulted in enhanced membrane properties in terms of water swelling, methanol uptake, methanol permeability, mechanical strength, and thermal stability, without significant loss of proton conductivity. All the blend membranes were transparent to visible light with presence of microphases in the order of 10–20 nm. When compared to parent SPEEK membranes, the new SPEEK/PPSU-A blend membranes showed slightly lower methanol permeability compared to neat SPEEK membrane. Membranes with 30 wt% phosphonic acid content with DP = 0.75 and 0.96, exhibited slightly higher proton conductivities at temperatures above 50 °C in comparison with Nafion membrane.

All the existing theories presuppose the continuity of oxygen chemical potential at interfaces between contiguous layers, in calculating steady-state chemical potential profiles across a multilayer composite of mixed conductor oxides that is subjected to an oxygen chemical potential gradient of whatsoever origin, but they have never been tested experimentally. We have observed that this continuity hypothesis appears to break down in yttria-stabilized zirconia/gadolinia-doped ceria bilayer electrolytes under an electric tension in ion-blocking condition (Hebb–Wagner polarization). It is suggested that all the continuity hypothesis-based existing theories to calculate the steady-state chemical potential distributions may not always be true depending on boundary conditions.

We investigated the conductivity of high-density bulk-anatase samples with a grain size between 24 and 56 nm prepared by high pressure field-assisted sintering. When exposed to humid atmosphere, the insurgence of proton conductivity was observed for temperatures below 350 °C. Below this temperature, the samples showed a conductivity several orders of magnitude higher than that measured under dry oxygen atmosphere. The protonic conductivity strongly increased as grain size decreased, while a negligible dependence from porosity was observed when the latter ranged between 8 and 25 vol%. If compared with zirconia- and ceria-based nanomaterials with similar grain size, bulk nanometric anatase showed the highest low temperature protonic conductivity as well as the highest crossover temperature between dry and humid conduction behavior.

Chemical degradation of the side-chain of perfluorosulfonic acid (PFSA) membranes by hydroxyl radicals (•OH) is examined with electronic structure calculations. The energetics associated with homolytic bond cleavage and for the sequence of reactions involved in the degradation was determined. Results show that the degradation of side-chain begins with the cleavage of the C–S bond. The sequence of reactions of the side-chain with •OH indicates scission of the backbone yielding reactive end-groups. The kinetics of the C–S bond cleavage was studied via: (i) reaction of anionic fragment with a •OH; and (ii) decomposition of fragment radical. The activation energy for the second pathway was calculated to be ∼11 kcal/mol lower requiring a change in symmetry of the molecular geometry of the sulfonate group from trigonal pyramidal to trigonal planar. This suggests that although the C–S bond may be the weakest in the side chain of a PFSA ionomer, its cleavage is kinetically hindered.

Elemental enrichment behavior on the surface of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) was investigated in order to understand potential degradation mechanism of solid oxide fuel cell cathodes. Surface morphological changes were examined using scanning electron microscopy after heat treatment in the temperature range of 600–900 °C. Submicron-sized precipitates were formed on grain surfaces after heat treatment. Their shapes appeared to be aligned along the surface orientations of the underlying grains. Auger electron spectroscopy and transmission electron microscopy characterization revealed that the precipitate was strontium (Sr)-oxygen (O) based. The formation of Sr–O precipitates was found to increase with increasing temperature and oxygen partial pressure. A defect chemistry model is presented based on the observed phenomena.

The compilation of measured effective rate constants for oxygen surface exchange on mixed conducting perovskites, which covers a great variety of compositions ranging from (La,Sr)MnO3−δ to (La,Sr)(Co,Fe)O3−δ and (Ba,Sr)(Co,Fe)O3−δ, demonstrates the importance of ionic conductivity—i.e., high oxygen vacancy concentration as well as vacancy mobility—as a key factor for the surface oxygen exchange rate. This interpretation is corroborated by ab initio calculations, which indicate that the approach of an oxygen vacancy to oxygen intermediates adsorbed on the surface is the rate determining step for a number of perovskites.

Nonstoichiometric mixed ionic and electronic conductors (MIECs) find use as oxygen permeation membranes, cathodes in solid oxide fuel cells, oxygen storage materials in three-way catalysts, and chemoresistive gas sensors. Praseodymium–cerium oxide (PrxCe1−xO2−δ) solid solutions exhibit MIEC behavior in a relatively high and readily accessible oxygen partial pressure () regime and as such serve as model systems for investigating the correlation between thermodynamic and kinetic properties as well as exhibiting high performance figures of merit in the above applications. In this paper, we extend recently published results for Pr0.1Ce0.9O2−δ to include values of x = 0, 0.002, 0.008, 0.1, and 0.20 (in PrxCe1−xO2−δ) to test how both defect and transport parameters depend on Pr fraction. Important observed trends with increasing x include increases in oxygen ion migration energy and MIEC and reductions in vacancy formation and Pr ionization energies. The implications these changes have for potential applications of PrxCe1−xO2−δ are discussed.

A systematic evaluation of the electrical conductivity of Sr-substituted YAlO3 system has been performed. A comparison between the Ca- and Sr-doped YAlO3 systems is reported. The samples have been synthesized by citrate gel route, and the electrical conductivity measurements have been conducted in air in the 300–800 °C temperature range. The influence of phase development of the compositions on the total conductivity has been investigated using the x-ray diffraction technique. Also, the effect of microstructure and composition of the phases evolved on the electrical conductivity has been analyzed using scanning electron microscopy and energy dispersive spectrum techniques.

Time stability of the solid oxide fuel cells (SOFCs) has been a significant concern toward realization of their practical applications. Its operation at elevated temperatures and in oxidizing atmospheres makes the cathode current collector one of the most vulnerable components of the SOFCs. Silver and silver-based metal oxide [lanthanum–strontium manganite (LSM) and yttria-stabilized zirconia] composites were investigated for the development of low-cost current collectors with long-term stability. While densification of pure silver limited its use as current collector, incorporation of oxide particles to the silver matrix led to formation of porous composites. However, addition of YSZ particles did not result in a stable porosity. Analysis of the impedance spectra allowed further investigations on the obtained microstructures and the formed contacts. No microstructural degradation has been observed in the porous Ag–LSM composite current collector and its electrical properties remained stable for over 5000 h of measurements at 800 °C in air.

Samples with overall composition HoxSr1−xCoO3−δ within the range 0.05 ≤ x ≤ 0.9 were prepared by a solid-state technique at 1100 °C in air. Single-phase HoxSr1−xCoO3−δ oxides were obtained within the range 0.05 ≤ x ≤ 0.30. Solid solutions of Ho0.05Sr0.95CoO3−δ and Ho0.1Sr0.9CoO3−δ were indexed in the cubic structure (Pm3m sp. gr.) with the unit cell parameters a = 3.846 Å and a = 3.842 Å, respectively. Further introduction of holmium leads to a change of crystal structure from cubic to a tetragonal 2ap × 2ap × 4ap superstructure. All samples with x > 0.3 were multiphase, containing a saturated solid solution with approximate composition Ho0.3Sr0.7CoO3−δ with Ho2O3 and CoO. The change of oxygen nonstoichiometry was measured by thermogravimetric analysis within the temperature range 25 ≤ T (°C) ≤ 1100. The absolute value of oxygen nonstoichiometry was calculated from the results of chromatometric titration. Thermal expansion coefficients of Ho1−xSrxCoO3−δ were measured by dilatometry within the temperature range 25 ≤ T (°C) ≤ 1100 in air.

The catalytic activity of Pt nanoparticles (NPs) significantly influences the electrochemical performance of direct methanol fuel cells. Information about the factors that influence the electrochemical activity of the catalyst themselves is scarce; hence, guidelines for the preparation of Pt NPs that yields the best performances are lacking. With consideration for this situation, we systematically investigated the relationship(s) between the characteristics of Pt NPs and their electrochemical performance. The general characteristics of Pt NPs, such as the average size, loading density, and dispersion status on the support, were varied in the presence of poly(acrylic acid)-wrapped multiwalled carbon nanotubes by controlling the preparation conditions, including the pH of the aqueous solution, the reaction temperature, and the reaction time. The enhanced catalytic activity is attributable to higher degree of dispersion, specific surface area, and electrochemically active surface area of Pt NPs. The optimized catalyst exhibits a ∼165% higher catalytic activity toward methanol oxidation than the commercial E-TEK.

Titanium-based ceramic supports designed for polymer electrolyte membrane fuel cells were synthesized, and catalytic activity was explored using electrochemical analysis. Synthesis of high surface area TiO2 and TiO supports was accomplished by rapidly heating a gel of polyethyleneimine-bound titanium in a tube furnace under a forming gas atmosphere. X-ray diffraction analysis revealed anatase phase formation for the TiO2 materials and crystallite sizes of less than 10 nm in both cases. Subsequent disposition of platinum through an incipient wetness approach leads to highly dispersed crystallites of platinum, less than 6 nm each, on the conductive supports. Scanning Electron Microscope (SEM)/energy dispersive x-ray analysis results showed a highly uniform Ti and Pt distribution on the surface of both materials. The supports without platinum are highly stable to acidic aqueous conditions and show no signs of oxygen reduction reactivity (ORR). However, once the 20 wt% platinum is added to the material, ORR activity comparable to XC-72-based materials is observed.

Seals are required for a functioning solid oxide fuel cell (SOFC). These seals must function at high temperatures of 600–900 °C and in oxidizing and reducing environments of the fuels and air. Among the different type of seals, the metal–ceramic seals require significant attention, research, and development because the brittle nature of ceramics and glasses leads to fracture and loss of seal integrity and functionality. A novel concept of self-healing/self-repairable glass seals is proposed, developed, and used for making metal–glass–ceramic seals for application in SOFC for enhancing reliability and life. Glasses and glass–ceramics displaying self-healing behavior are investigated and used to fabricate seals. The performance of these seals under long-term exposure at higher temperatures coupled with thermal cycling is characterized. Self-repairability of these glass seals is also demonstrated by leak tests along with the long-term performance. An approach for studying the kinetics of crack healing in glasses and glass–ceramics responsible for self-repair is briefly described.