Direct ammonia proton-conducting solid oxide fuel cells prepared by a modified suspension spray

A dense (BCSO) membrane was fabricated by a modified suspension spraying on porous NiO–BCSO anode support. In the process, the suspension was directly prepared by ball-milling the BaCO₃, CeO₂, and Sm₂O₃ powders in ethanol. A dense and uniform electrolyte layer in the thickness of 10 μm was successfully prepared on porous anode support by suspension spray process after co-sintering at 1,400 °C for 5 h. With (NSMO) cathode, a single cell was assembled and tested with hydrogen and ammonia as fuels, respectively. The hydrogen-fueled cell exhibits 1.01 V for open circuit voltage (OCV) and 560 mW/cm² for peak power density at 700 °C. In comparison, the cell in ammonia displays a similar performance (1.02 V for OCV and 530 mW/cm² for output), which indicates the liquid ammonia is a promising substitute for hydrogen. Moreover, the fuel cell displays good interface contacts. To sum up, ammonia-fueled solid oxide fuel cells prepared by this simple suspension spray is an alternative way to promote the commercialization.     

Preparation and characterization of iron oxide thin films by spray pyrolysis using methanolic and ethanolic solutions

Iron oxide thin films have been obtained by spray pyrolysis using 100% methanolic and ethanolic solutions of iron tri-chloride. The films were deposited onto ITO-coated glass substrates. The preparative conditions have been optimized to obtain compact, pin-hole-free and smooth thin films which are adherent to the substrate. The structural, morphological and compositional characterizations have been carried out by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The films deposited using ethanolic solution results into pure hematite; α-Fe₂O₃ thin films, however, films deposited using methanolic solution consists of hematite and maghemite-c phases of iron oxide. The films are nanocrystalline with particle size of 30-40 nm. The optical absorbance of the film was of the order of 10⁵ cm⁻¹. The optical band gap of films was found to be 2.26 and 2.20 eV for the films deposited using methanolic and ethanolic solutions, respectively.     

(La0.75Sr0.25)(Cr0.5Mn0.5)O3/YSZ composite anodes for methane oxidation reaction in solid oxide fuel cells

The synthesis and performance of (La_0.75Sr_0.25)(Cr_0.5Mn_0.5)O₃/Y₂O₃–ZrO₂ (LSCM/YSZ) composites are investigated as alternative anodes for the direct utilization of methane (i.e., natural gas) in solid oxide fuel cells. Addition of YSZ phase greatly improves the adhesion and reduces the electrode polarization resistance of the LSCM/YSZ composite anodes. LSCM/YSZ composite anodes show reasonably good performance for the methane oxidation reaction in wet CH₄ and the best electrode performance was achieved for the composite with LSCM contents of 50–60 wt.% with polarization resistances of 2–3 Ω cm² in 97% CH₄/3% H₂O at 850 °C. The electrode impedance for the methane oxidation in wet CH₄ on the LSCM/YSZ composite anodes was characterized by three separable arcs and the electrode behavior could be explained based on the ALS model for the reaction on the MIEC electrode. The results indicate that electrocatalytic activity of the LSCM/YSZ composite anodes for the methane oxidation is likely limited by the oxygen vacancy diffusion in the substituted lanthanum chromite-based materials.     

Gas sensing properties of nanostructured MoO3 thin films prepared by spray pyrolysis

Thin films of molybdenum trioxide (MoO₃) were deposited on common glass using the chemical spray pyrolysis technique. A (NH₄)₆Mo₇O₂₄4H₂0 solution 0.1 M was used as the precursor one. The influence of substrate temperature on the crystallographic structure, surface morphology and electrical behavior of MoO₃ thin films was studied. MoO₃ can exist in two crystalline forms, the thermodynamically stable orthorhombic α-MoO₃ and the metastable monoclinic β-MoO₃ phase. XRD-spectra showed a growth of α-MoO₃ phase percentage as substrate temperature increases from 420 K up to 670 K. Films deposited in the 500–600 K range have a clearly porous surface structure of nanometer order as can be seen in SEM images. Changes up to six magnitude orders were observed in MoO₃ thin films electrical resistance when films temperature varied from 100 K up to 500 K. The sensing property of these MoO₃ films was also studied. The sensitivity was investigated in the temperature range 160 and 360 K for H₂O and CO gases, respectively. Both of them are of reducing nature. In all studied cases sensitivity decreases slowly as film temperature is raised. At room temperature the sensitivity changes from 12 up to 75% depending on substrate temperature. The sensitivity for CO gas was found to be lower than that of H₂O.     

Stable and high conductivity ceria/bismuth oxide bilayer electrolytes for lower temperature solid oxide fuel cells

A highly conductive bismuth oxide/ceria bilayer electrolyte was developed to reduce solid oxide fuel cell (SOFC) operating temperatures. Bilayer electrolytes were fabricated by depositing a layer of Er_0.2Bi_0.8O_1.5 (ESB) of varying thickness via pulsed laser deposition and dip-coating on a Sm_0.2Ce_0.8O_1.9 (SDC) substrate. The open-circuit potential (OCP) and ionic transference number (t _i) of ESB/SDC electrolytes were tested in a fuel cell arrangement as a function of relative thickness, temperature, and with H₂/H₂O and CO/CO₂ on the anode side and air on the cathode side. These EMF measurements showed a significant increase in OCP and t _i with the bilayer structure, as compared to the cells with a single SDC electrolyte layer. Furthermore, improvement in the OCP and t _i of bilayer SOFCs was observed with increasing relative thickness of the ESB layers. Hence, the bilayer structure overcomes the limited thermodynamic stability of bismuth oxides and prevents electronic conductivity of ceria-based oxides in reducing atmosphere.     

The influence of pore and Ni morphology on the electrical conductivity of porous Ni/YSZ composite anodes for use in solid oxide fuel cell applications

A wide range of porous Ni–YSZ composite microstructures was produced by conventional tape casting and co-sintering using a variety of starting powders including Ni, NiO, graphite and Ni-coated graphite. The graphite additions were added to produce controlled levels of porosity in the final sintered and reduced anode. All materials indicated classical conductivity percolation behaviour with increasing Ni loadings. However, the percolation threshold at which electrical conduction became measurable was lowest for anodes made with Ni-coated graphite and highest for anodes containing large amounts of porosity introduced by large additions of graphite. Sintered and reduced anodes possessed large scale porosity introduced by the graphite additions and a finer scale porosity generated by the incomplete sintering of the Ni/YSZ powder network. A model was developed for predicting the influence of large scale porosity on conductivity and agreed well with the experimental results. The analysis indicates that fine scale porosity will have a more detrimental impact on conductivity compared to a coarse porous structure.     

Electrochemical characterization of Mn: Co3O4 thin films prepared by spray pyrolysis via aqueous route

Present investigation reports, spray pyrolytic deposition of Mn: Co₃O₄ thin films onto the stainless steel by spray pyrolysis, at the deposition temperature 573 ± 2 K via aqueous route. Prepared electrodes were characterized structurally and morphologically by means of XRD and SEM. Also optical and electrochemical characterizations were carried out in depth. Structural characterization confirms face centered cubic and tetragonal body centered crystal structures for Co₃O₄ and Mn₃O₄ respectively. The rough granular morphology is observed form SEM. Electrochemical study reveals the pseudo capacitive as well as double layer behavior with optimum specific capacitance 485.29 F/g at the scan rate 1 mV/s in 1 M KOH electrolyte. Specific energy, specific power and columbic efficiency were calculated using chronopotentiometric technique. Electrochemical impedance spectroscopy was carried out in the frequency range 1 mHz–1 MHz. Randles equivalent circuit parameters associated with the operative cell are reported.