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The structure stability, conductivity and electrochemical properties of Cr-substituted La0.3Sr0.7FeO3-d SOFC electrode materials were investigated in this work, primarily for application in symmetrical solid oxide fuel cells. Cr substitution, giving La0.3Sr0.7Fe1-xCrxO3-d (LSFC, x = 0, 0.2, 0.3), remarkably improves the phase stability of La0.3Sr0.7FeO3-d materials in reducing atmospheres and their redox tolerance in varying atmospheres. Symmetrical half-cells employing La0.3Sr0.7Fe0.8Cr0.2O3-d on La0.8Sr0.2Ga0.8Mg0.2O3-d (LSGM) electrolyte supports exhibit electrode polarization resistances (RP) of as low as 0.25 O*cm2 in air and 0.45 O*cm2 in humidified H2 at 750oC. Maximum power densities of 0.30 W/cm2 (800oC) and 0.22 W/cm2 (750oC) were obtained for a symmetrical single cell using humidified H2/air. The excellent anodic and cathodic electrochemical performance of LSFC is thought to be due to its high electrical conductivity (180 and 0.43 S*cm-1 at 700oC in air and 10%H2+N2, respectively) and good ionic conductivity.

An AC/DC spark anodizing method was used to coat the aluminum-copper (Al-Cu) alloy AA2219 with oxide films to protect them form corrosion. The effect of electrolyte solution composition and the lifetime use of the anodizing solution on the anodizing process and the oxide film properties have been investigated. In this work, an anodizing solution containing 0.15 M KOH and various concentrations of Na2SiO3 has been used. Oxide film characterizations were carried out using scanning electron microscopy (SEM) and energy dispersive x-ray (EDX). Corrosion assessment was carried out using linear sweep voltammetgram (LSV) in borate buffer solution (pH 7).

This work uses the Wagner Factor as a qualitative means of explaining the effects that perturbing the oxygen content in La1-xSrxMnO3{plus minus}d (LSM) cathodes has on their O2 redox activity and as well as the emergence of pseudo-capacitive characteristics under low pO2 atmospheres. The Wagner Factor correlates the rate constant of the O2 redox reaction in mixed conducting perovskites (kchem, Dchem) to changes in the oxide's oxygen concentration. The emergence of an oxygen under- stoichiometric (3-d) state under low O2 partial pressures and/or at high cathodic overpotentials is believed to lead to the observed electrochemical capacitive behavior.

In Solid Oxide Fuel Cells, Ni-YSZ cermets have many advantages, but degradation can be severe if the anode is exposed to an oxidizing environment. It has been found, in this study and others, that the primary cause of degradation is due to a >60% volume change from Ni to Ni oxide. It is shown here that the Ni is reduced and oxidized in a shorter time period for each redox cycle after the first full cycle. For reduction, this is likely due to the development of a larger surface area, as the cellular NiO surface structure is observed. Also, controlled oxidation of the anode leads to reduced series and reaction resistance values and the Van der Pauw technique indicates that the conductivity of the Ni-YSZ electrode improves after the first redox cycle. Thus, as long as there is enough space for the Ni to expand as it is oxidized, there are actually benefits to cell performance from redox cycling.

An ordered mesporous Colloid Imprinted Carbon with 80 nm sized pores (CIC80), a nitrided CIC80 (N-CIC80), and Ta oxynitride nanoparticles on nitrided CIC80 (TaOxNyNPs/N-CIC80) were synthesized and evaluated as possible supports for Pt electrocatalysts in PEMFC applications. Transmission electron microscopy images showed that they have the expected pore size and that the TaOxNyNPs are in the range of 5-20 nm in diameter. Potential stepping experiments revealed that the TaOxNyNPs/N-CIC80 composite exhibits the highest corrosion resistance in 0.5 M H2SO4, followed by N-CIC80 and then CIC80. Consistent with this, cyclic voltammetry revealed that the TaOxNyNPs/N-CIC80 composite gave the smallest increase in surface area after the potential stepping experiment, followed by N-CIC80 and CIC80. These results suggest that a nitrided carbon surface is more corrosion resistant than carbon alone, and that the TaOxNyNPs, which are themselves extremely stable, are conferring some of their stability to the carbon substrate.

Lowering the operating temperatures of solid oxide fuel cells (SOFCs) to below 600 °C is projected to enhance the long term stability of these devices by slowing down thermally induced microstructural changes in the electrodes. To minimize the electrode resistance caused by the lowered operating temperatures, the fabrication of nanocomposite Ni-YSZ thin film electrodes with high triple phase boundary (tpb) lengths is a possible approach. However, these nanocomposite electrodes will still undergo microstructural changes that could cause performance degradation. Here, it is shown that the long-term stability of nanocomposite Ni-YSZ anodes can be enhanced by the deposition of a thin, poroous, YSZ coating on the outer surface of the Ni-YSZ electrodes, preventing Ni diffusion out of the pores followed by Ni particle formation. A degradation rate of 0.072 Ω·cm2/hour was observed for the standard Ni-YSZ nanocomposite thin film anode, whereas a much lower degradation rate of 0.011 Ω·cm2/hour was achieved after applying the YSZ coating.

In the present study, thin film Ni anodes, prepared by liquid precursor deposition on dense YSZ substrates, were analyzed by electrochemical impedance spectroscopy (EIS) in a humidified H2environment at 500 to 700 °C, with the activation energy of 1.30 eV ascribed to the charge transfer reaction at the Ni – YSZ - gas triple phase boundary (tpb). For comparison, the same Ni precursor was infiltrated into a porous YSZ scaffold and was also then characterized by EIS analysis. A transmission line model was used to analyze the EIS data obtained from the infiltrated Ni-YSZ composite anodes, allowing the separation of the effects of ionic transport in the YSZ network and the impedance due to the electrochemical reaction at the tpb. The activation energy for the latter process was determined to be the same as for the model thin film Ni anode, suggesting that Ni/YSZ interfaces prepared in the form of Ni thin films on YSZ substrate and Ni-YSZ composites by the deposition of the same polymeric Ni precursor exhibit comparable impedance behavior.

Symmetrical full cells, based on La0.3M0.7Fe0.7Cr0.3O3-δ(M = Sr, Ca) perovskite oxide electrodes, were constructed, using a Yttria-stabilized zirconia (YSZ) electrolyte with a Samaria-doped ceria (SDC) buffer layer, and then tested in a range of fuel environments at 800 oC. It is demonstrated that the Ca analog (La0.3Ca0.7Fe0.7Cr0.3O3-δ-LCFCr) is an equally good fuel electrode (anode) and air electrode (cathode) as the Sr member of this family (LSFCr), exhibiting very good electrochemical performance in H2, CO and H2+CO atmospheres. LCFCr and LSFCr anodes were also evaluated in the presence of 9 ppm H2S exposures, showing a small, but reproducible and reversible, decrease in polarization resistance (Rp). Studies at cell polarizations of -100 and -300 mV from the open circuit full cell voltage showed a ca. 2-4 % increase in current density in the presence of 9 ppm H2S + 30 % H2, with the cell recovering fully when H2S was removed.

Our recent studies have shown that La0.3Ca0.7Fe0.7Cr0.3O3-δ(LCFCr) is a promising material as an air electrode for use in reversible solid oxide cells, due to its excellent activity towards the oxygen reduction and oxygen evolution reactions, along with its good thermal expansion coefficient match with common electrolytes, such as gadolinium-doped ceria (GDC). In the present work, GDC was infiltrated into a pre-sintered, porous, LCFCr scaffold, forming a porous layer on the LCFCr surface. This resulted in further improvements in the electrochemical performance, due to the enhanced ionic conductivity introduced by the GDC phase. The impedance spectroscopy results showed that GDC addition lowered the resistance specifically of the high frequency process.

The structure stability, conductivity and electrochemical properties of Cr-substituted La0.3Sr0.7FeO3-δ SOFC electrode materials were investigated in this work, primarily for application in symmetrical solid oxide fuel cells. Cr substitution, giving La0.3Sr0.7Fe1-xCrxO3-δ (LSFC, x = 0, 0.2, 0.3), remarkably improves the phase stability of La0.3Sr0.7FeO3-δ materials in reducing atmospheres and their redox tolerance in varying atmospheres. Symmetrical half-cells employing La0.3Sr0.7Fe0.8Cr0.2O3-δ on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte supports exhibit electrode polarization resistances (RP) of as low as 0.25 Ω•cm2 in air and 0.45 Ω•cm2 in humidified H2 at 750oC. Maximum power densities of 0.30 W/cm2 (800oC) and 0.22 W/cm2 (750oC) were obtained for a symmetrical single cell using humidified H2/air. The excellent anodic and cathodic electrochemical performance of LSFC is thought to be due to its high electrical conductivity (180 and 0.43 S•cm-1 at 700oC in air and 10%H2+N2, respectively) and good ionic conductivity.

Sr-doped and Sr-free La1-xSrxMn1-yCryO3{plus minus}δ (LSMC) perovskite-type oxides were synthesized and tested for use as intermediate temperature anodes for SOFC applications. Thermo-chemical and chemical stabilities were tested in hydrogen and low ppm H2S: H2 at 800åC. Relative reducibility was determined by temperature program reduction using thermo-gravimetric analysis. This was correlated with oxygen non-stoichiometry determined by permanganate titration. The final phase after reduction at 1100åC was determined by powder X-ray diffraction and the ability of these materials to recover after reduction was tested by re-sintering in air. Electrochemical testing revealed catalytic activity towards hydrogen as a function of changing sintering temperature and operating temperature, as well as Sr and Cr content LSMC materials were found to be chemical stable in upto 10 ppm H2S in humidified hydrogen at 800åC, and Sr-free LMC materials were shown to have reasonable catalytic activity towards the hydrogen oxidation reaction at 700 and 800åC.