The steady-state oxygen permeation through polycrystalline La 2 NiO 4+␦ , synthesized by a citric acid-based technique and sintered at 1350°C, has been measured as a function of oxygen gradient, temperature ͑850-1000°C͒, and membrane thickness ͑0.3-2.5 mm͒. In agreement with earlier reports, the La 2 NiO 4+␦ membranes show high permeation rates, comparable to those found for the perovskite-related La 1−x Sr x Co 1−y Fe y O 3−␦ materials. The self-diffusion coefficient and the surface exchange coefficient of oxygen are extracted from the data through transport modeling using averaged bulk transport parameters and through numerical analysis based on a one-dimensional finite-element method. The self-diffusion coefficient and surface exchange coefficients show Arrhenius-type behavior with activation energies 40 ± 20 and 110 ± 60 kJ/mol, respectively, and agree qualitatively with literature data obtained by 16 O 2 / 18 O 2 exchange/secondary ion mass spectroscopy analysis at lower temperatures.

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In situ powder X-ray diffraction has been used to study NiO supported on NiAl 2 O 4 during several reductionoxidation cycles, mimicking chemical looping combustion. Hydrogen and methane were used as fuel (reducing agents). Direct reduction and reoxidation of NiO/Ni is observed, and NiAl 2 O 4 remained inert during the reduction and reoxidation processes. Thermogravimetric analyses of the material under the same reducing conditions, using a 90-210 µm particle fraction suitable for fluidized-bed applications, showed that, first, a rapid reduction occurs where oxygen transport to the particle surface not is rate-limiting. The rapid reduction is followed by a much slower reduction, where oxygen transport through the particle is expected to be ratelimiting. The fast reduction reaction is determined to be first order, with respect to H 2 , whereas an order slightly smaller than unity is observed when using CH 4 as a reducing agent. Reoxidation is observed to be first order, with respect to O 2 . At low reactive gas concentrations, the reaction rates decreases in the following order: CH 4 > H 2 > O 2 .

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Various inorganic membranes have demonstrated good capability to separate hydrogen from other gases at elevated temperatures. Hydrogen-permeable, dense, mixed proton-electron conducting ceramic oxides offer superior selectivity and thermal stability, but chemically robust candidates with higher ambipolar protonic and electronic conductivity are needed. In this work, we present for the first time the results of various investigations of La1−xSrxCrO3−∂ membranes for hydrogen production. We aim in particular to elucidate the material’s complex transport properties, involving co-ionic transport of oxide ions and protons, in addition to electron holes. This opens some new possibilities for efficient heat and mass transfer management in the production of hydrogen. Conductivity measurements as a function of pH2 at constant pO2 exhibit changes that reveal a significant hydration and presence of protons. The flux and production of hydrogen have been measured under different chemical gradients. In particular, the effect of water vapor in the feed and permeate gas stream sides was investigated with the aim of quantifying the ratio of hydrogen production by hydrogen flux from feed to permeate and oxygen flux the opposite way (“water splitting”). Deuterium labeling was used to unambiguously prove flux of hydrogen species.