Oleg Bobrenok

Cathodic materials for intermediate-temperature solid oxide fuel cells based on praseodymium nickelates-cobaltites

A unique combination of methods (TPD of O2, thermogravimetry, isotopic heteroexchange of oxygen in different modes) was used to carry out detailed studies of oxygen mobility and reactivity in mixed praseodymium nickelates-cobaltites (PrNi1 − xCoxO3 + δ) and their composites with doped cerium dioxide (Ce0.9Y0.1O2 − δ) as promising cathodic materials stable towards the effect of CO2 in the intermediate-temperature region. It is shown that in the case of composites of PrNi1 − xCoxO3+δ-Ce0.9Y0.1O2 − δ synthesized using the Pechini method and ultrasonic treatment, stabilization of the disordered cubic perovskite phase due to redistribution of cations between the phases provides high oxygen mobility. Preliminary results on tests of cathodic materials of this type supported on planar NiO/YSZ anodes (H.C. Starck) with a thin layer of YSZ electrolyte and a buffer Ce0.9Y0.1O2 − δ layer showed that power density of up to 0.4 W/cm2 was reached in the region of medium (600–700°C) temperatures, which was close to typical values for fuel cells of this type with cathodes based on strontium-doped perovskites and their composites with electrolytes.

Design of medium–temperature solid oxide fuel cells on porous supports of deformation strengthened Ni–Al alloy

An approach was developed towards design of medium-temperature solid-oxide fuel cells based on a deformation strengthened Ni-Al alloy. Methods of sintering were described that allowed obtaining layers of complex oxides with ionic and mixed conductivity and with regulated porosity in the range of 40–1%. Power density of a fuel cell on a metallic support reaches 500 mW/cm2 already at 700°C when humid H2 was used as fuel and air was used as an oxidant. Analysis of fuel cell cross-section after tests showed absence of fractures, flaking, and new phases with low conductivity, which proves good compatibility of all materials used in fuel cell design.

Single fuel cell with supported LSM cathode

Single fuel cells with bilayer supported cathodes are manufactured and tested. The cathodes consist of a high-porous La0.6Sr0.4MnO3 support with the thickness of approximately 1 mm and a functional composite layer with the thickness of 13–15 μm made of La0.75Sr0.2MnO3 and 8YSZ. Voltammetric and power characteristics of single fuel cells with a supported cathode, thin-film YSZ electrolyte, and platinum cathode are determined. The conclusion as to the significant contribution into the polarization overpotential losses on the cathode is made on the basis of the measurements of electric fuel cell characteristics. It decreases significantly as a result of the supported cathode modification by praseodymium oxide. At 850°C and voltage of 0.81 V, electric power density of a fuel cell was 1.65 W/cm2.

Doped Nanocrystalline Pt-Promoted Ceria-Zirconia as Anode Catalysts for IT SOFC: Synthesis and Properties

Ceria-zirconia samples doped with Gd, Pr, Sm, or La cations were prepared via Pechini route and promoted by Pt. Effect of their real structure and surface properties (characterized by neutronography, EXAFS, XPS, FTIRS of adsorbed CO) on the mobility and reactivity of the lattice oxygen (by oxygen isotope exchange and CH 4 TPR) was analyzed. For the reaction of CH 4 steam reforming (SR), catalytic performance is determined both by Pt dispersion and lattice oxygen mobility. Ni-YSZ anodes promoted by these catalysts possess a stable and efficient performance in CH 4 SR in the 600-800°C range in stoichiometric feeds without coking.

Design and Characterization of Nanocomposites Based on Complex Perovskites and Doped Ceria as Advanced Materials for Solid Oxide Fuel Cell Cathodes and Membranes

La 0.8 Sr 0.2 Fe 0.6 Ni 0.4 O 3-x - Ce 0.9 Gd 0.1 O 2-x and La 0.8 Sr 0.2 Fe 0.8 Co 0.2 O 3-x - Ce 0.9 Gd 0.1 O 2-x nanocomposites were synthesized via ultrasonic dispersion of nanocrystalline powders of perovskite and fluorite oxides in acetone with addition of a surfactant, followed by drying and sintering at temperatures up to 1200°C. The evolution of the structure of samples with sintering temperature was studied by XRD and TEM with EDX and compared with the data on conductivity, oxygen isotope exchange, O 2 TPD, H 2 and CH 4 TPR. Preliminary testing of button-size cells with cathodes supported on thin YSZ layer covering Ni/YSZ cermet demonstrated a high and stable performance of LSNF–GDC composite promising for the practical application.

Advanced Sintering Techniques in Design of Planar IT SOFC and Supported Oxygen Separation Membranes

Thin film solid oxide fuel cells (SOFC) operating in the intermediate temperature (IT) range are now considered as promising for distributed, mobile, standby or auxiliary power generation. At present one of the most important scientific aims in design of solid oxide fuel cells is to lower the operating temperatures to 600-800 С. In this temperature range, majority of problems inherent to SOFC operating at high (950-1000 C) are alleviated. Thus, cations interdiffusion and solid state reactions between electrolyte and electrodes are hampered and thermal stresses are decreased which prevent degradation of the functional layers [Yamamoto, 2004 ]. Hence, design of thin film SOFC requires also elaboration of nanostructured electrodes compatible with electrolytes from chemical and thermophysical points of view and providing a developed three-phase boundary (TPB). In this respect, broad options are provided by design of nanocomposite mixed ionic-electronic conducting (MIEC) functional layers – (Sadykov et al., 2010; Sadykov et al., 2009; Sadykov et al., 2008).

Metal Supported SOFC on the Gradient Permeable Metal Foam Substrate

Gradient permeable metallic substrate material consisting of two layers of NiAl alloy was developed for the SOFC design. The open-cell foam layer (thickness 1-2 mm, cell density 60 ppi) provides the structure robustness, while a thin (100-200 μm) mesoporous layer facilitates supporting functional layers. Cathode layers (LSM, LSFN and their nanocomposites with GDC or YSZ) and anode layers (NiO/YSZ, NiO/YSZ +Ru/Ln-Sr-Mn-Cr-O nanocomposite catalyst) were deposited by slip casting, electrophoretic deposition or air brushing. Thin (5-10 μm) YSZ layer was deposited by MO CVD. Power density up to 550 mW/cm2 at 700oC was obtained on button-size cells using wet H2-air feeds.

Solid oxide fuel cells with film electrolytes prepared by chemical vapor deposition

Basing on the developed film formation technique by organometallic chemical vapor deposition (organometallic CVD), thin films of electrolytes were prepared on supporting anode and experiments were carried out to optimize the cathodic layer forming conditions. The individual electrochemical cell achieved the specific power of 1190, 800, and 350 mW/cm2 at the temperatures of 800, 700, and 600°C, respectively. Operation of a 13 cm2 fuel cell in solid oxide fuel cell (SOFC) battery was studied.

Design of Anodes for IT SOFC: Effect of Complex Oxide Promoters and Pd on Activity and Stability in Methane Steam Reforming of Ni/YSZ (ScSZ) Cermets

Effect of fluorite-like or perovskite-like complex oxide promoters and Pd on the performance of Ni/YSZ and Ni/ScSZ cermets in methane steam reforming or selective oxidation by O 2 into syngas at short contact times was studied. Spatial uniformity of dopants distribution in composites was controlled by TEM combined with EDX, while the lattice oxygen mobility and reactivity was elucidated by CH 4 and H 2 TPR. Oxide promoters allow to operate even at stoichiometric H 2 O/CH 4 ratio by suppressing coke deposition through modification of Ni surface, while doping by Pd ensures reasonable performance at moderate (∼550 °C) temperatures required for Intermediate–Temperature Solid Oxide Fuel Cells (IT SOFC).

Gradient composite metal-ceramic foam as supportive component for planar SOFCs and MIEC membranes

A novel approach to the design of planar gradient porous supports for the thin-film SOFCs and MIEC membranes is described. The supports thermal expansion is controlled by the creation of a two-component composite metal-ceramic foam structure. Thin MIEC membranes and SOFCs were prepared on the composite supports by the layerwise deposition of composite functional layers including complex fluorites and perovskites. Lab-scale studies demonstrated promising performance of both MIEC membrane and SOFC.