Gaseous nitrogen has a wide variety of applications in industry. Currently, nitrogen is produced by energy-intensive cryogenic fractional distillation of liquefied air, pressure swing adsorption (PSA), and membranes. In this paper, a novel process was proposed and experimentally verified for production of nitrogen. In this process, oxygen in air is extracted through a dense oxygen–permeable membrane, which is then reacted with methane. By optimizing the air and methane flow rate, the process can produce nearly pure nitrogen as well as a syngas (a mixture of CO and H2). At 800 °C, the reactor produced nitrogen at a rate of 9.2 mL cm–2·min–1 with purity over 99%, and methane was reformed to syngas with CH4 throughput conversion over 90%, H2 selectivity of 92%, and CO selectivity of 92%. The syngas can be burned to generate heat or used as intermediate chemicals for production of liquid fuels and hydrogen. Since the membrane reactor is driven by the energy released by the reaction and does not consume high grade energy electricity, it has a much higher overall energy efficiency than the current industrial nitrogen separation processes.

•Porous LSGM backbone was fabricated by phase inversion tape casting method.•Nano-scale and symmetrical SrFe0.75Mo0.25O3-δ electrodes were developed.•A total polarization resistance of 0.17 Ω cm2 was achieved at 800 °C.•Symmetrical solid oxide fuel cells yield 703 mW cm−2 in H2 at 800 °C.The new phase inversion tape casting method is explored to fabricate the “porous|dense|porous” La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) with aligned straight pores. Symmetrical fuel cells are obtained by impregnating nano-scale SrFe0.75Mo0.25O3-δ (SFMO) catalysts into both porous LSGM scaffolds. Operation on hydrogen and air oxidants produces 401, 521, 602 and 703 mW cm−2 at 650, 700, 750 and 800 °C, respectively. Impedance measurements show that the overall interfacial polarization resistances are 0.17, 0.20, 0.25 and 0.36 Ω cm2 for such symmetrical fuel cells at 800, 750, 700 and 650 °C, respectively. Impedance analysis under varied oxygen partial pressures indicates that the symmetrical SFMO-LSGM electrodes exhibit lower polarization resistances for phase-inversion casted LSGM scaffolds than for the traditionally casted LSGM scaffolds.

•Tri-layered “porous | dense | porous” La0.8Sr0.2Cr0.5Fe0.5O3−δ-Zr0.84Y0.16O2−δ oxygen transport membranes were fabricated.•La0.6Sr0.4Co0.2Fe0.8O3−δ and Ce0.8Sm0.2O1.9−δ/Ni nano-scale catalysts on porous layers were developed.•Oxygen evolution reactions dominated the total resistances to oxygen permeation.•4.3 ml cm−2 min−1 oxygen permeability was yield at 800 °C under the air/CH4 gradient.Tri-layered “porous | dense | porous” La0.8Sr0.2Cr0.5Fe0.5O3−δ-Zr0.84Y0.16O2−δ (LSCrF-YSZ) oxygen transport membranes (OTMs) were fabricated and permeation resistances from oxygen reduction and evolution reactions were determined by using Hebb-Wagner polarization method after introducing additional electron-blocking YSZ thin layers within the dense LSCrF-YSZ layers. Adding nano-scale catalysts, i.e. La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCoF) on air side and Ce0.8Sm0.2O1.9−δ/Ni (SDC/Ni) on CH4 side, into the porous LSCrF-YSZ layers yielded substantially reduced interfacial polarization resistances, and thereby allowed for high oxygen permeability at reduced temperatures under the air/CH4 gradient, e.g., 1.1 and 4.3 ml cm−2 min−1 at 650 and 800 °C, respectively. Analysis of the impedance spectra suggest that the oxygen reduction kinetics on air side was probably limited by charge transfer reaction at T ≥ 750 °C and surface oxygen exchange at T ≤ 700 °C. Meanwhile, oxygen evolution reactions on CH4 side dominated the total resistances to oxygen permeation through the tri-layered OTMs.

•New SOFC anodes are fabricated by impregnating Ce1−xZrxO2−δ catalysts into 430L scaffolds.•Nano-Ce0.7Zr0.3O2−δ@430L anodes show the highest activity for hydrogen oxidation.•Nano-Ce0.7Zr0.3O2−δ@430L anode fuel cells yield power densities of 1.24 W cm−2 at 800 °C.Ceria–zirconia solid solution nanoparticulates, Ce1−xZrxO2−δ (x = 0, 0.2, 0.3, 0.4, 0.6, 0.8 and 1.0), are impregnated into the porous 430L stainless steel scaffolds and evaluated as the anode catalysts for solid oxide fuel cells (SOFCs). Combined analyses of X-ray diffraction and Raman scattering reveal the fluorite cubic (c) structure up to x ≤ 0.3 transforms to a mixture of the cubic and metastable tetragonal (t″) phases for 0.4 ≤ x ≤ 0.8, with the onset of tetragonal distortions at x = 0.8. Temperature-programmed reduction in H2 indicates that doping Zr4+ into the ceria lattice could improve the oxygen storage capacity. Nonetheless, the charge transfer process within the bulk Ce1−xZrxO2−δ or across the interfaces of Ce1−xZrxO2−δ|YSZ becomes increasingly sluggish at x ≥ 0.3. The two opposite effects yield the smallest anode polarization resistances at x = 0.3, e.g., 0.08 ± 0.01 Ω cm2 for Ce0.7Zr0.3O2−δversus 0.24 ± 0.02 Ω cm2 for CeO2−δ or 0.26 ± 0.04 Ω cm2 for Ce0.4Zr0.6O2−δ at 800 °C. Furthermore, thin YSZ electrolyte fuel cells with impregnated La0.6Sr0.4Fe0.9Sc0.1O3−δ – YSZ cathode supports produce peak power densities of 1.24 W cm−2 at 800 °C for nano-Ce0.7Zr0.3O2−δ@430L anodes, approximately 80% higher than 0.67–0.70 W cm−2 on nano-CeO2−δ@430L or nano-Ce0.4Zr0.6O2−δ@430L anodes.

•Carbon nanotubes are in situ produced by exposing LaNi0.6Fe0.4O3−δ in methane.•LaNi0.6Fe0.4O3−δ/CNT hybrids are highly active for methane electro-oxidation.•Direct methane fuel cells yield 1.00 W cm−2 at 800 °C and 0.73 W cm−2 at 750 °C.Here we report the use of LaNi0.6Fe0.4O3−δ/carbon nanotube (LNF/CNT) hybrids as novel and robust anode catalysts that are in situ fabricated by exposure of nano-scale LNF perovskite oxide catalysts to slightly humidified methane. TEM observations confirm the formation of CNTs with the inner diameter and the wall thickness both at ≈15 nm. Combined XRD and EDX analyses show that LNF oxides decompose into a mixture of La2O3, FeNi3 alloy and LaFeO3, where FeNi3 alloy particles have an average diameter of 45 nm, largely exist outside of these CNTs and are surrounded by nano-scale La2O3 and LaFeO3 oxides. The LNF/CNT hybrids exhibit superior catalytic activities for methane oxidation reactions, yielding low anode polarization resistances of 0.22 Ω cm2 at 800 °C and 0.44 Ω cm2 at 750 °C. Impregnated fuel cells with such hybrid anodes display stable and excellent power densities in methane fuels. e.g., 1.00 W cm−2 at 800 °C and 0.73 W cm−2 at 750 °C.

•La0.6Sr0.4Fe0.9Sc0.1O3−δ oxides show good stability in both oxidizing and reducing environments.•La0.6Sr0.4Fe0.9Sc0.1O3−δ electrodes exhibit polarization resistances of 0.015 Ω cm2 in air and 0.29 Ω cm2 in H2 at 800 °C.•Maximum power densities of 0.56 W cm−2 are obtained at 800 °C for symmetrical La0.6Sr0.4Fe0.9Sc0.1O3−δ electrode fuel cells.The main barrier to symmetrical solid oxide fuel cells (SOFCs), where the same catalytic materials are used simultaneously as the anodes and the cathodes, is to identify a redox-stable catalyst that exhibits superior catalytic activities for both fuel oxidation and oxygen reduction reactions. Here we report a Sc-substituted La0.6Sr0.4FeO3−δ oxide, La0.6Sr0.4Fe0.9Sc0.1O3−δ, that shows great promise as a new symmetrical electrode material with good structural stability and reasonable conductivities in air and hydrogen. We further demonstrate that nano-scale La0.6Sr0.4Fe0.9Sc0.1O3−δ catalysts impregnated into the porous La0.9Sr0.1Ga0.8Mg0.2O3−δ backbones exhibit good catalytic activities for oxygen reduction and hydrogen oxidation reactions and thereby yield low polarization resistances, e.g., 0.015 Ω cm2 in air and 0.29 Ω cm2 in hydrogen with appropriate current collection at 800 °C. Thin La0.9Sr0.1Ga0.8Mg0.2O3−δ electrolyte fuel cells with such symmetrical La0.6Sr0.4Fe0.9Sc0.1O3−δ catalysts showed maximum power densities of 0.56 and 0.32 W cm−2 when operating on 97% H2–3% H2O at 800 and 700 °C, respectively.

•Novel metal-supported SOFCs are fabricated by tape casting and co-sintering.•LSFSc oxides are used as symmetric electrode catalysts by impregnation method.•Nano-scale LSFSc catalysts are highly active for electrodes reactions.This paper reports on the fabrication of novel metal-supported solid oxide fuel cells containing porous 430L stainless steel substrates, YSZ electrolytes and porous YSZ cathode backbones. Such tri-layer structures are obtained by the tape casting, lamination and co-firing techniques. Redox-stable La0.6Sr0.4Fe0.9Sc0.1O3−δ (LSFSc) oxides are introduced as symmetric electrode catalysts onto the internal surfaces of porous 430L substrates and YSZ backbones using the solution impregnation method. The maximum power density is 0.65 W cm−2 measured at 800 °C. Impedance analyses show that the anode polarizations are the largest losses while the cathode polarizations make negligible contribution to the total cell resistances.

•SrFe0.75Mo0.25O3−δ–La0.9Sr0.1Ga0.8Mg0.2O3−δ composites are fabricated using the liquid phase impregnation method.•The nano-scale SrFe0.75Mo0.25O3−δ cathodes exhibit area specific resistances of 0.04 Ω cm2 in air at 800 °C.•Impedance analysis shows that ionization of adsorbed oxygen is the rate-limiting step for oxygen reduction reactions.This paper describes the structure and electrochemical properties of composite cathodes for solid oxide fuel cells fabricated by infiltration of aqueous solutions corresponding to SrFe0.75Mo0.25O3−δ (SFMO) into porous La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) backbones. XRD measurement confirms the predominance of the perovskite SFMO oxides in the infiltrates together with some minor impurities of SrMoO4 after calcinations at 850–1100 °C. The cathode polarization resistance as obtained from impedance measurement on symmetric cathode fuel cells exhibits a pronounced increase as a function of calcinations temperature due to increased SFMO particle sizes, e.g., 0.04 Ω cm2 for 70 nm-sized catalysts calcinated at 850 °C versus 0.11 Ω cm2 for 400 nm-sized catalysts calcinated at 1100 °C. Oxygen partial pressure and temperature dependence of impedance data shows that oxygen reduction kinetics is largely determined by ionization of adsorbed oxygen atoms on the SFMO catalysts.

•Metal-supported fuel cells are based upon porous 430L |dense YSZ| porous YSZ structures.•Nominal SrFe0.75Mo0.25O3−δ oxides are impregnated as symmetrical catalysts.•Promising power densities of 0.74 W cm−2 are obtained at 800 °C.Barriers to technological advancement of metal-supported SOFCs include nickel coarsening in the anode, metallic interdiffusion between the anode and the metal substrate, as well as poor cathode adhesion. Here we report a robust and novel architectured metal-supported SOFC that consists of a thin dense yttria-stabilized zirconia (YSZ) electrolyte layer sandwiched between a porous 430L stainless steel substrate and a porous YSZ thin layer. The key feature is simultaneous use of impregnated nano-scale SrFe0.75Mo0.25O3−δ coatings on the internal surfaces of the porous 430L and YSZ backbones respectively as the anode and cathode catalyst. Such a fuel cell exhibits power densities of 0.74 W cm−2 at 800 °C and 0.40 W cm−2 at 700 °C when operating on hydrogen fuels and air oxidants.

•SmBa0.5Sr0.5Co2O5+δ/LSGM cathode of nanostructure is fabricated by impregnation method.•The lowest ARS values of SmBa0.5Sr0.5Co2O5+δ/LSGM cathode is 0.035 Ω cm2 at 550 °C and 0.12  Ω cm2 at 500 °C.•Power densities of 1.5 W cm−2 at 600 °C and 0.70 W cm−2 at 500 °C were obtained.Here we report the fabrication of composite cathodes for reduced-temperature solid oxide fuel cells by impregnating aqueous solutions corresponding to SmBa0.5Sr0.5Co2O5 (SBSCO) into the porous La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) backbones. Examination of X-Ray diffraction patterns indicates that phase-pure SBSCO layered perovskite oxides can be only achieved at calcination temperatures ≥900 °C. Based upon impedance measurement of symmetric cells, the SBSCO–LSGM composites calcinated at 850 °C show a trade-off between the SBSCO phase purity and catalyst size, and thereby exhibit minimal cathode polarization resistances with respect to the infiltrate calcination temperature, e.g., 0.035 Ω cm2 at 550 °C and 0.12 Ω cm2 at 500 °C at the loadings of 21 wt%. Analysis of impedance spectra under varied oxygen partial pressures suggests that oxygen reduction reactions on the nano-scale SBSCO–LSGM composite are largely dominated by ionization of adsorbed oxygen atoms on the SBSCO surfaces. Thin LSGM electrolyte fuel cells with impregnated Ni anodes and SBSCO cathodes show high power densities of 1.5 W cm−2 at 600 °C and 0.70 W cm−2 at 500 °C.

•Infiltrated SmBa0.5Sr0.5Co2O5+δ cathode for MS–SOFC is evaluated.•Polarization resistance of the cathode is 0.054 Ω cm2 at 700 °C.•No degradation is found after the 35 thermal cycles for the cathode.•Power density output of the fuel cell can be as high as 1.25 W cm−2 at 700 °C.This paper reports the fabrication of the SmBa0.5Sr0.5Co2O5+δ (SBSCO) infiltrated scandia–stabilized–zirconia (SSZ) composite cathode for metal–supported solid oxide fuel cells (MS–SOFCs). The effects of the calcination temperature on the structure, morphology and polarization resistance of the composite cathode were studied. Cathode calcinated at 700 °C showed the finest microstructure and the lowest polarization resistance, e.g., 0.054 and 0.172 Ω cm2 at 700 and 600 °C, respectively. Thermal shock resistance of the composite cathode was studied and no degradation was found after the 35 thermal cycles conducted between 100 and 600 °C with a rate of 10 °C min−1. MS–SOFC with the SBSCO infiltrated SSZ cathode was prepared and the maximum power density (MPD) can be as high as 1.25, 0.92, 0.61 and 0.39 W cm−2 when measured at 700, 650, 600 and 550 °C, respectively.

•Metal-supported SOFCs are fabricated by tape casting and co-sintering.•Cell performance of 907 mW cm−2 at 800 °C is obtained.•Possible degradation mechanisms are investigated.Metal-supported solid oxide fuel cells (MS-SOFCs) containing porous 430L stainless steel supports, YSZ electrolytes and porous YSZ cathode backbones are fabricated by tape casting, laminating and co-firing in a reducing atmosphere. Nano-scale Ni and La0.6Sr0.4Fe0.9Sc0.1O3−δ (LSFSc) coatings are impregnated onto the internal surfaces of porous 430L and YSZ, acting as the anode and the cathode catalysts, respectively. The resulting MS-SOFCs exhibit maximum power densities of 193, 418, 636 and 907 mW cm−2 at 650, 700, 750 and 800 °C, respectively. Nevertheless, a continuous degradation in the fuel cell performance is observed at 650 °C and 0.7 V during a 200-h durability measurement. Possible degradation mechanisms were discussed in detail.

Highly active Ni-cermet anodes for thin La0.9Sr0.1Ga0.8Sr0.2O3-δ (LSGM) electrolyte solid oxide fuel cells are fabricated by impregnating aqueous nickel nitrate solutions into porous LSGM backbones, followed by calcinations at 700 °C. High Ni loadings, e.g., VNi = 7.9%, are mandatory for obtaining well-interconnected Ni coatings on the internal surfaces of the supporting LSGM structures, where good chemical compatibility is confirmed by the X-Ray diffraction patterns. The polarization resistances are impressively low for the VNi = 7.9% anodes in humidified hydrogen, ranging from 0.008 Ω cm2 at 650 °C to 0.011 Ω cm2 at 550 °C. Thin LSGM electrolyte fuel cells, impregnated with Ni anodes and Sm0.5Sr0.5CoO3−δ–Ce0.8Sm0.2O1.9 (SSC – SDC) cathodes, exhibit superior power densities at reduced temperatures, e.g., 1.60 and 1.05 W cm−2 at 650 and 550 °C, respectively.Highlights► Dual-scale porous Ni–LSGM composites are fabricated using impregnation method. ► Low ASR values of 0.011 Ω cm2 are obtained at 550 °C for the Ni–LSGM composite anodes. ► Power densities of 1.05 W cm−2 are obtained at 550 °C for LSGM-electrolyte fuel cells.

•The Mn1.5Co1.5O4 impregnated YSZ composites show cathode polarization resistances of 0.43 Ω cm2 at 800 °C.•Co-impregnation of Mn1.5Co1.5O4–Sm0.2Ce0.8O2−δ can reduce the cathode polarization resistances to 0.15 Ω cm2 at 800 °C.•Oxygen reduction kinetics is dominated by double ionization of adsorbed oxygen atoms or charge transfer reactions.The composite cathodes of yttria stabilized zirconia (YSZ) and Mn1.5Co1.5O4 (MCO) are prepared by infiltration of the MCO oxides into porous YSZ backbones using aqueous solutions of the corresponding nitrate salts. Calcinations at 850 °C promote the formation of the MCO spinel oxide and yield nano-scale catalyst coatings on the YSZ pore walls. Impedance measurements on the symmetric MCO–YSZ cathode fuel cells show that the lowest polarization resistance in air at 800 °C is 0.43 Ω cm2 for the MCO impregnated YSZ composite at the MCO volume loading of 13.5%. Analysis of the impedance spectra suggest that the oxygen reduction kinetics is probably limited by double ionization of the adsorbed oxygen atoms or charge transfer at the triple-phase boundaries. Furthermore, introducing the oxide ion conductor of samarium-doped ceria as a second component in the coated catalysts yields much lower polarization resistances, e.g., 0.15 Ω cm2 at 800 °C.

Here we report solid oxide cells with thin strontium- and magnesium-doped lanthanum gallate electrolytes that yield power densities of 1.06 W cm−2 at 550 °C and 0.81 W cm−2 at 500 °C when operated on humidified hydrogen and ambient air. Cost-effective ceramic processing and chemical solution impregnation methods were utilized, yielding a dual micron- and nano-scale architecture that is essential for achieving good low-temperature performance.

Thin film solid oxide fuel cells, composed of thin coatings of 8 mol% Y2O3-stabilized ZrO2 (YSZ), thick substrates of infiltrated La0.8S0.2FeO3 (LSF)–YSZ cathodes and CuO–SDC (Ce0.85Sm0.15O1.925)–ceria anodes, are fabricated using the conventional tape casting and infiltration methods. Infiltrated LSF–YSZ cathodes exhibit a much lower interfacial polarization resistance than (La0.8Sr0.2)0.98MnO3 (LSM)–YSZ cathodes due to the mixed ionic and electronic conducting behavior of LSF, especially at low operation temperatures. The single cell has shown good and stable performance in hydrogen and hydrocarbon fuels. Maximum power densities for hydrogen, propane, dodecane and low sulfur diesel at 800 °C are 0.62 W cm−2, 0.40 W cm−2, 0.37 W cm−2 and 0.36 W cm−2, respectively.Highlights► Cu–SDC cermet anodes enable fuel flexible operation of SOFCs. ► LSF infiltrated cathodes exhibit low interfacial polarizations. ► Maximum power densities of 0.36–0.40 W cm−2 are obtained at 800 °C for propane, dodecane and low sulfur diesel.

Low temperature anode-supported solid oxide fuel cells with thin films of samarium-doped ceria (SDC) as electrolytes, graded porous Ni-SDC anodes and composite La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)–SDC cathodes are fabricated and tested with both hydrogen and methanol fuels. Power densities achieved with hydrogen are between 0.56 W cm−2 at 500 °C and 1.09 W cm−2 at 600 °C, and with methanol between 0.26 W cm−2 at 500 °C and 0.82 W cm−2 at 600 °C. The difference in the cell performance can be attributed to variation in the interfacial polarization resistance due to different fuel oxidation kinetics, e.g., 0.21 Ω cm2 for methanol versus 0.10 Ω cm2 for hydrogen at 600 °C. Further analysis suggests that the leakage current densities as high as 0.80 A cm−2 at 600 °C and 0.11 A cm−2 at 500 °C, resulting from the mixed electronic and ionic conductivity in the SDC electrolyte and thus reducing the fuel efficiency, can nonetheless help remove any carbon deposit and thereby ensure stable and coking-free operation of low temperature SOFCs in methanol fuels.Highlights► Low-temperature ceria electrolyte SOFCs are fabricated with finely structured anodes. ► Maximum power densities of 260–820 mW cm−2 are obtained at 500–600 °C for direct methanol utilization. ► Leakage current densities as high as 0.80 A cm−2 at 600oC and 0.11 A cm−2 at 500 °C help remove carbon deposits and thereby ensure stable and coking-free operation.

This paper describes results on the electrochemical reduction of carbon dioxide using the same device as the typical planar nickel–YSZ cermet electrode supported solid oxide fuel cells (H2–CO2, Ni–YSZ|YSZ|LSCF–GDC, LSCF, air). Operation in both the fuel cell and the electrolysis mode indicates that the electrodes could work reversibly for the charge transfer processes. An electrolysis current density of ≈1 A cm−2 is observed at 800 °C and 1.3 V for an inlet mixtures of 25% H2–75% CO2. Mass spectra measurement suggests that the nickel–YSZ cermet electrode is highly effective for reduction of CO2 to CO. Analysis of the gas transport in the porous electrode and the adsorption/desorption process over the nickel surface indicates that the cathodic reactions are probably dominated by the reduction of steam to hydrogen, whereas carbon monoxide is mainly produced via the reverse water gas shift reaction.

Thin film solid oxide fuel cells (SOFCs), composed of thin coatings of 8 mol% Y2O3-stabilized ZrO2 (YSZ) and thick substrates of (La0.8Sr0.2)0.98MnO3 (LSM)–YSZ cathodes, are fabricated using the conventional tape casting and tape lamination techniques. Densification of YSZ electrolyte thin films is achieved at 1275 °C by adjusting the cathode tape formulation and sintering characteristics. Two types of copper cermets, CuO–YSZ–ceria and CuO–SDC (Ce0.85Sm0.15O1.925)–ceria, are compared in terms of the anodic performance in hydrogen and propane. Maximum power densities for hydrogen and propane at 800 °C are 0.26 W cm−2 and 0.17 W cm−2 for CuO–YSZ–ceria anodes and 0.35 W cm−2 and 0.22 W cm−2 for CuO–SDC–ceria anodes, respectively. Electrochemical impedance analysis suggests that CuO–SDC–ceria exhibits a much lower anodic polarization resistance than CuO–YSZ–ceria, which could be explained by the intrinsic mixed oxygen ionic and electronic conductivities for SDC in the reducing atmosphere.