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The kinetically sluggish oxygen evolution reaction in proton exchange membrane water electrolyzers (PEMWEs) leads to high potentials of >1.5 V vs RHE at the anode electrode during operation. In contrast, an investigation with an in situ reference electrode indicates a much lower potential at the anode side of the bipolar plate which would allow the use of stainless steel and carbon as the bipolar plate materials. This decoupling is induced by the low conductivity of the circulating deionized water. In single cell electrolyzer tests, we show that carbon-coated 316L (C-316L) stainless steel is suitable as a bipolar plate material in contact with the anode and cathode sides of the PEMWE. The coating remains stable throughout the experiments, i.e., 720 h at the anode and 1000 h at the cathode side. Based on these results we regard carbon-coated stainless steel as a sustainable solution for the large-scale application of PEM water electrolysis since it might replace (Pt-coated) titanium in the bipolar plate.

The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometry and electrical conductivity in layered LaBaCo2O5+δ double perovskite was studied as a function of temperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo2O5+δ double perovskite was obtained by annealing cubic A-site cation disordered La0.5Ba0.5CoO3-δ perovskite at 1100 °C in N2. High temperature X-ray diffraction between room temperature (RT) and 800 °C revealed that LaBaCo2O5+δ remains tetragonal during heating in oxidizing atmosphere, but goes through two phase transitions in N2 and between 450 °C and 675 °C from tetragonal P4/mmm to orthorhombic Pmmm and back to P4/mmm due to oxygen vacancy ordering followed by disordering of the oxygen vacancies. An anisotropic chemical and thermal expansion of LaBaCo2O5+δ was demonstrated. La0.5Ba0.5CoO3-δ remained cubic at the studied temperature irrespective of partial pressure of oxygen. LaBaCo2O5+δ is metastable with respect to La0.5Ba0.5CoO3-δ at oxidizing conditions inferred from the thermal evolution of the oxygen deficiency and oxidation state of Co in the two materials. The oxidation state of Co is higher in La0.5Ba0.5CoO3-δ resulting in a higher electrical conductivity relative to LaBaCo2O5+δ. The conductivity in both materials was reduced with decreasing partial pressure of oxygen pointing to a p-type semiconducting behavior. [ABSTRACT FROM AUTHOR]

Ga-substitutedLa3Zr2Li7O12garnet isshown to be a promising Li-ion conducting electrolyte material. Thestrategy adopted in this study is the substitution of Li by Ga, therebycreating Li vacancies and enhancing the Li conductivity. Solid StateMagic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) measurementshave been used to identify the location of the substituted Ga in thestructure and its effect on the Li distribution and mobility. In additionMAS NMR was used to follow the effect of protonation due to atmosphericmoisture on the sintering behavior of these materials. In particular,it is shown that the Ga atoms are located in tetrahedral positionspromoting the random distribution of lithium over the available sites,hence promoting an increase in the conductivity. Control of the sinteringconditions by using a dry O2atmosphere leads to the formationof dense ceramic materials and avoids the degradation process dueto the exchange of Li+by H+from atmosphericmoisture. Electrochemical Impedance Spectroscopy data show total conductivitiesas high as 1.3 and 2.2 mS cm–1at 24 and 42 °C,respectively, which are among the highest Li ion conductivities reportedfor garnet-structured materials to date. [ABSTRACT FROM AUTHOR]

Abstract: A complex layered oxide has been synthesised as bulk material starting from the theoretical n =2 R-P formula Sr3(Mg x Mo1 − x )2O7 − δ (x ≈0.25). This compound exhibits an unexpected crystal chemistry illustrated by the coexistence of several stacking modes — principally the ordered double perovskite Sr2MgMoO6 − δ and n =2 R-P type phase — inside the same crystallite. Chemical EDS analyses performed by TEM techniques have lead to an average chemical formula Sr2.68Mg0.64Mo1.67, which differs from the expected n =2 R-P formula Sr3Mg0.5Mo1.5O7 − δ in particular through a significant Sr deficiency. From high resolution electron microscopy (HREM) and Z-contrast (SuperSTEM) images, this analytical result is interpreted by the formation of a complex intergrowth [(Sr,Mg)3Mo2O7]1 − x [Sr2MgMoO6] x with x ≈0.4. The resulting structure can be interpreted as a compositional segregation between Mg2+ and Mo6+ species in two basic structures, namely Sr3Mo2O7 and Sr2MgMoO6. [Copyright &y& Elsevier]

Abstract: Microstructural evolution of Ce0.8Gd0.2O1.9/NiO (CGO/NiO) co-infiltrated nanoparticles in Sr0.94Ti0.9Nb0.1O3–Zr0.84Y0.16O1.92 (STN94–YSZ) anodes for solid oxide fuel cells (SOFCs) is investigated during electrochemical testing in a symmetric cell setup. The CGO/NiO infiltrated symmetric cells were subjected to varying atmospheres of H2O/H2 between 650 and 850 °C and characterized by electrochemical impedance spectroscopy. Analytical high resolution transmission electron microscopy showed that the CGO/NiO infiltrate was found to coalesce and grow from an indistinguishable CGO/NiO fluorite structure of an average diameter of 5 nm to individual well-connected, but phase-separated, CGO and Ni particles of 50 nm in average. This study confirms that instability and growth of CGO/NiO infiltrates in STN-based SOFC electrodes affect the morphology and can potentially be linked to reported losses in electrochemical performance. [Copyright &y& Elsevier]

Compositionally engineered a La 1-x Ba x CoO 3-δ -(1- a ) BaZr 0.9 Y 0.1 O 2.95 ( a = 0.6, 0.7, 0.8 and x = 0.5, 0.6, 0.7) (LBZ) nanocomposite cathodes were prepared by oxidation driven in situ exsolution of a single-phase material deposited on a BaZr 0.9 Y 0.1 O 2.95 electrolyte. The processing procedure of the cathode was optimized by reducing the number of thermal treatments as the single-phase precursor was deposited directly on the electrolyte. The exsolution and firing of the cathodes occurred in one step. The electrochemical performance of symmetrical cells with the compositionally engineered cathodes was investigated by impedance spectroscopy in controlled atmospheres. The optimized materials processing gave web-like nanostructured cathodes with superior electrochemical performance for all compositions. The area specific resistances obtained were all below 12 Ω·cm 2 at 400 °C and below 0.59 Ω·cm 2 at 600 °C in 3% moist synthetic air. The resistances of the nominal 0.6 La 0.5 Ba 0.5 CoO 3-δ -0.4 BaZr 0.9 Y 0.1 O 2.95 and 0.8 La 0.5 Ba 0.5 CoO 3-δ -0.2 BaZr 0.9 Y 0.1 O 2.95 composite cathodes were among the lowest reported for protonic ceramic fuel cells cathodes in symmetrical cell configuration with ASR equal to 4.04 and 4.84 Ω·cm 2 at 400 °C, and 0.21 and 0.27 Ω·cm 2 at 600 °C, respectively.

The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometry and electrical conductivity in layered LaBaCo₂O 5+δ double perovskite was studied as a function of temperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo₂O 5+δ double perovskite was obtained by annealing cubic A-site cation disordered La 0.5 Ba 0.5 CoO 3-δ perovskite at 1100 °C in N₂. High temperature X-ray diffraction between room temperature (RT) and 800 °C revealed that LaBaCo₂O 5+δ remains tetragonal during heating in oxidizing atmosphere, but goes through two phase transitions in N₂ and between 450 °C and 675 °C from tetragonal P4/mmm to orthorhombic Pmmm and back to P4/mmm due to oxygen vacancy ordering followed by disordering of the oxygen vacancies. An anisotropic chemical and thermal expansion of LaBaCo₂O 5+δ was demonstrated. La 0.5 Ba 0.5 CoO 3-δ remained cubic at the studied temperature irrespective of partial pressure of oxygen. LaBaCo₂O 5+δ is metastable with respect to La 0.5 Ba 0.5 CoO 3-δ at oxidizing conditions inferred from the thermal evolution of the oxygen deficiency and oxidation state of Co in the two materials. The oxidation state of Co is higher in La 0.5 Ba 0.5 CoO 3-δ resulting in a higher electrical conductivity relative to LaBaCo₂O 5+δ . The conductivity in both materials was reduced with decreasing partial pressure of oxygen pointing to a p-type semiconducting behavior.