The practical use of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) prototypical oxygen-transport membrane for air separation is currently hampered by the decomposition of the cubic perovskite into a variant with ...hexagonal stacking at intermediate temperatures of ≤850 °C, which impairs the oxygen transport. Here, we report the development of a W-doped BSCF composite that contains Fe-rich single perovskite (SP) and W-rich double perovskite (DP) phases with different crystallographic parameters. In contrast to BSCF, the BSCFW SP/DP composite maintains its cubic structure at 800 °C for 200 h, demonstrating its structural stability at intermediate temperatures. We use X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy to show that the enhanced phase stability of the composite is associated with a temperature-induced SP–DP dynamic interaction, which involves W and Fe interdiffusion between the SP and DP phases, dynamically adjusting the chemical composition and limiting structural distortion and new phase formation. The composite exhibits a stable permeation performance in the oxygen-transport membrane during over 150 h operation at 800 and 700 °C, confirming the potential of intermediate-temperature oxygen-transport membranes for air separation and providing insight for designing thermally stable composite oxides.
Adding value with membranes: Improved methane aromatization was achieved by using an oxygen‐permeable membrane. The resulting membrane reactor shows a superior methane conversion and a higher ...resistance towards catalyst deactivation.
Utilizing advanced transmission electron microscopy (TEM), the structure at the (110)-type twin boundary (TB) of Ce-doped GdFeO3 (C-GFO) has been investigated with picometer precision. Such a TB is ...promising to generate local ferroelectricity within a paraelectric system, while precise knowledge about its structure is still largely missing. In this work, a direct measurement of the cation off-centering with respect to the neighboring oxygen is enabled by integrated differential phase contrast (iDPC) imaging, and up to 30 pm Gd off-centering is highly localized at the TB. Further electron energy loss spectroscopy (EELS) analysis demonstrates a slight accumulation of oxygen vacancies at the TB, a self-balanced behavior of Ce at the Gd sites, and a mixed occupation of Fe2+ and Fe3+ at the Fe sites. Our results provide an informative picture with atomic details at the TB of C-GFO, which is indispensable to further push the potential of grain boundary engineering.
Utilizing advanced transmission electron microscopy (TEM), the structure at the (110)-type twin boundary (TB) of Ce-doped GdFeO
(C-GFO) has been investigated with picometer precision. Such a TB is ...promising to generate local ferroelectricity within a paraelectric system, while precise knowledge about its structure is still largely missing. In this work, a direct measurement of the cation off-centering with respect to the neighboring oxygen is enabled by integrated differential phase contrast (iDPC) imaging, and up to 30 pm Gd off-centering is highly localized at the TB. Further electron energy loss spectroscopy (EELS) analysis demonstrates a slight accumulation of oxygen vacancies at the TB, a self-balanced behavior of Ce at the Gd sites, and a mixed occupation of Fe
and Fe
at the Fe sites. Our results provide an informative picture with atomic details at the TB of C-GFO, which is indispensable to further push the potential of grain boundary engineering.
A novel method for the preparation of a thin oxidic proton‐conducting electrolyte is presented. This kind of supported film was studied in detail as it is applicable for IT–SOFC, H2 membranes, and ...advanced catalytic converters. Thin‐film (∼5 μm) proton‐conducting membranes with the nominal composition BaZr0.85Y0.15O3−δ (BZY) were prepared over porous Ni–8YSZ/Ni–BZY substrates by the solid‐state reaction of a gastight 8YSZ layer and a coated BaCO3 layer. The resulting asymmetric membranes are of a homogeneous composition and are gastight. Indeed, XRD analysis showed a highly crystalline cubic perovskite. The solid‐state reaction promoted the formation of (i) an electrolyte with very fine (∼100 nm) grains and high packing density and (ii) an unexpected porous needle‐like top layer with a nominal composition similar to that of the protonic electrolyte, to which it is intimately attached. The layer morphology, phase distribution, and lattice composition were investigated by EDS–SEM, EDX as well as SIMS. Conduction properties of the protonic material were investigated by DC conductivity of pressed bars under different gas compositions and also by impedance spectroscopy of a supported thin film.
Solid oxide protonic fuel cells are one of the most efficient means of directly converting stored chemical energy to usable electrical energy. Acceptor-doped Ba(Zr, Ce)O3 perovskite-type oxides are ...the preferred electrolyte choice as they provide higher conductivity due to lower activation energy. While substantial progress has been made on small-sized protonic laboratory-scale cells, a considerable challenge has been upscaling robust planar-type devices. This paper employs a cost-effective inverse tape casting route and screen printing to fabricate flat planar anode-supported protonic fuel cells consisting of NiO-SrZr0.5Ce0.4Y0.1O3-δ substrate, SrZr0.5Ce0.4Y0.1O3-δ electrolyte, and BaCo0.4Fe0.4Zr0.1Y 0.1O3-δ as the cathode. The processing parameters were analyzed and adjusted to obtain defect-free single cells of dimension up to 100 mm × 100 mm × 0.5 mm with diminished warping. In addition, the smooth tri-layered green tapes yielded suitably dense and gas-tight electrolyte layers after co-sintering at 1300 °C/5 h. Finally, the electrochemical performance of the 50 × 50 mm2 SrZr0.5Ce0.4Y0.1O2.95 based cells was evaluated, and their impedance spectra were deconvoluted to identify all performance-related polarization processes via the distribution of relaxation time.
•Fabrication of 50 × 50 mm2 planar type SrZr0.5Ce0.4Y0.1O3-δ based ceramic fuel-cell using a scalable tape casting route.•Bi-layered green tapes yielded suitably dense and gas-tight electrolyte layers after co-sintering at 1300 °C/5 h.•NiO-SrZr0.5Ce0.4Y0.1O3-δ composite cement as an alternative anode for PCFCs.•The peak power density reached 172 m W cm−2 at 600 °C and can be improved further.
A novel membrane reactor consisting of Ce0.9Gd0.1O2−δ–Gd0.1Sr0.9Fe0.9Ti0.1O3−δ (CGO–GSFT) is used to combine air separation with biogas reforming in a single unit. The composite material CGO–GSFT was ...synthesized via a combined EDTA–citrate complexing sol–gel method. Characterization with XRD, SEM, and EDXS revealed that the composite material was a two-phase fluorite–perovskite system with good compatibility and a homogeneous percolative network. XRD demonstrated that the CGO–GSFT membrane shows a good phase stability not only in CO2 but also in simulated biogas atmosphere. Under the gradient of air/simulated biogas, the oxygen permeability and methane conversion was increased by either raising the operating temperature or increasing the CO2 concentration. At 890 °C and a CH4/CO2 molar ratio of 1.5, an oxygen permeation flux of 1.1 cm3 min–1 cm–2 through the CGO–GSFT membrane was achieved while methane conversion reached 83%, and remained stable for nearly 150 h before the measurement was intentionally stopped.
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