Silvia Licoccia

Nafion/Tin Oxide Composite Membranes for Direct Methanol Fuel Cells

Composite Nafion-based membranes were prepared and characterized, using hydrated tin oxide as a filler. Water Uptake and proton conductivity were measured as a function of temperature. Methanol crossover through reference Nafion and composite membranes was evaluated by a voltametric method and the electrochemical performance of the membranes was assessed by tests in a single direct methanol fuel cell (DMFC). The formation of the composite improved the properties of Nafion matrix in terms of methanol crossover and DMFC performance, allowing to identify Nafion membrane with 10wt% tin oxide as a suitable electrolyte to be used in a DMFC device operating at T ≥ 90°C. ©The Electrochemical Society.

Low temperature sol-gel preparation of β-Al2TiO5 thin films: spectroscopic analysis of the precursors

Two sol-gel syntheses allowed the preparation of β-Al2TiO5 thin films on silicon substrates at 700°C, reacting aluminum and titanium alkoxides with and without acetylacetone as a chelating agent. Nuclear magnetic resonance (NMR) and mass spectra of the sols allowed identification of the intermediate species formed and to show the formation of an Al-Ti containing polymer establishing that the synthesis without acetylacetone leads to the most extensive polymerization. The formation of β-Al2TiO5 at low temperatures is attributed to diffusion-limited crystallization process, which takes place in the conditions of high homogeneity at molecular level reached in the sol-gel synthesis. The crystallization of the films was studied as a function of the firing time and temperature and confirmed that β-Al2TiO5 with better thermal stability was obtained with the synthesis without chelating agent.

Layered Titanates Intercalating Organic Guest Spacers for Organic/Inorganic Proton Conductors

Two layered organic/inorganic tetratitanate derivatives containing sulfanilic acid (SA) were synthesized from potassium tetratitanate (K2Ti4O9) or its acid form (H2Ti4O9). Scanning electron microscopy (SEM) observations were performed to investigate the microstructural features of the samples. The thermal stability of the compounds was tested by thermogravimetric analysis (TGA). The effect of the presence of organic guest molecules in the layered tetratitanates was investigated in terms of proton exchange capacity (PEC) and conductivity (σ), to evaluate the use of these compounds as fillers for nanocomposite proton exchange membranes for fuel cell applications.

Pulsed Laser Deposition of Superlattices Based on Ceria and Zirconia

Rapidly growing attention is being recently directed towards the investigation of the ionic conducting properties of oxide film hetero-structures. Experimental evidence has been reported showing that interfacial phenomena at hetero-phase interfaces give rise to faster ion conduction pathways than the bulk or homo-phase interfaces. Nonetheless, a deeper understanding of the interface transport properties is still needed to exploit these effects. In this work, we have investigated the growth mechanism of different superlattices fabricated by pulsed laser deposition (PLD) coupling doped and undoped cerium and zirconium oxides. Single crystalline MgO wafers were selected as deposition substrates. The superlattice structures were obtained by means of a thin buffer layer of SrTiO3 (STO). The growth mechanism was investigated by reflection high energy electron diffraction (RHEED) and X-ray diffraction (XRD) analyses.

Phase Stability and Electrochemical Analysis of Nb Doped BaCe0.9Y0.1O3-x Electrolyte for IT-SOFCs

Barium cerate-based electrolytes containing different amounts of Nb5+ as a dopant were investigated with the aim of attaining materials with improved chemical stability. BaCe0.9-xNbxY0.1O3-x(BCYN) powders with different compositions (0 ≤ x ≤ 0.20) were synthesized by citrate–nitrate auto-combustion method and pure single phases were obtained at 1000 °C. Dense pellets were obtained using sintering a temperature of 1450 °C for 10 hours. The chemical stability was evaluated by XRD analysis after CO2 exposure at 700°C for 3 hours. To investigate the effect of Nb5+ doping on conductivity, electrochemical impedance spectroscopy(EIS) measurements were carried out in the 400–700 °C temperature range in different atmospheres.

Fabrication of Proton Conducting Solid Oxide Fuel Cells by using Electrophoretic Deposition

Anode-supported proton conducting solid oxide fuel cells (SOFCs) were fabricated by using electrophoretic deposition (EPD) for the electrolyte film deposition. BaCe0.9Y0.1O3-δ (BCY10) thick films were deposited on NiO-BCY10 substrates. The influence of the EPD parameters on the microstructure and electrical properties of BCY10 thick films was investigated. The anode substrates and electrolyte deposits were co-sintered at 1550 degrees C for 2 h to obtain a dense electrolyte thick film, while keeping a suitable porosity in the anode. Innovative composites with La0.8Sr0.2Co0.8Fe0.2O3 (LSCF)-BaCe0.9Yb0.1O3-δ (10YbBC) composition were used as cathode materials. Prototype SOFCs were prepared by depositing the composite cathode on the co-sintered half cells. Fuel cell tests and electrochemical impedance spectroscopy (EIS) measurements were performed in the 550–700 degrees C temperature range. The maximum power density of 296 mW cm-2 was achieved at 700 degrees C.

Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) based on a Proton Conducting Electrolyte

Single chamber solid oxide fuel cells (SC-SOFCs) are promising for portable power applications because they are simpler than the conventional dual-chamber cells. SC-SOFCs based on the cell Ni/BaCe0.3Zr0.5Y 0.2O3-δ (BCZY)/Ba0.5Sr 0.5Co0.8Fe0.2O3-δ (BSCF) were investigated under gas mixtures of propane (C3H8), oxygen (O2), and helium (He) with different compositions. To enhance the fuel partial oxidation at low temperatures, a porous layer of Ru was added onto the anode surface. Two configurations, finger (with parallel electrodes) and sandwich (with electrodes on opposite sides of the pellets), were analyzed. ©The Electrochemical Society.

Copper Doped Lanthanum Strontium Ferrite as Cathode for La0.8Sr0.2Ga0.8Mg0.2O3

A “cobalt free” cathode material with stoichiometric composition La0.8Sr0.2Fe0.8Cu0.2O3 (LSFCu) was specifically developed for La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) electrolyte. The chemical stability with LSGM electrolyte was investigated by structural and morphological analysis. The electrochemical properties of LSFCu dense pellets were investigated in the temperature range 600–750°C by electrochemical impedance spectroscopy (EIS). LSFCu/LSGM/LSFCu symmetrical cells were prepared and Area Specific Resistance (ASR) values, directly depending on the rate limiting step of the oxygen reduction reaction, were evaluated. Fuel cells were prepared using LSFCu as cathode material on LSGM pellet and electrochemical tests were performed and compared to similar fuel cells prepared by using commercial La0.6Sr0.4Fe0.8Co0.2O3(LSFCo). The maximum current density and power density recorded for LSFCu and LSFCo were comparable demonstrating that Cu can be used as substitutes Co.

Soft Chemistry Routes for the Synthesis of Sr0.02La0.98Nb0.6Ta0.4O4 Proton Conductor

Niobates and tantalates of rare-earth compounds are high temperature proton conductor (HTCP) oxides that are gaining attention as possible stable electrolyte materials for application in intermediate temperature solid oxide fuel cells (IT-SOFCs). Sr0.02La0.98Nb0.6Ta0.4O4 was synthesized by auto-combustion and co-precipitation routes, and by solid state reaction for sake of comparison, expecting an improvement in conductivity for the wet chemistry routes over the conventional solid state reaction method. Single phase materials were obtained at 1100°C by autocombustion and by co-precipitation. The synthesized powders were characterized by X-ray diffraction (XRD) and dilatometric analyses. Dense electrolytes were obtained by pressing the calcined powders into cylindrical pellets and then sintering at 1600°C for 10 h. The pellets were observed by scanning electron microscopy (SEM). Electrical conductivity of the sintered pellets was measured as a function of the temperature by electrochemical impedance spectroscopy (EIS) measurements. Proton conductivity of 2.2×10-4 S cm-1 was obtained in wet argon atmosphere at 800°C for the sample produced via auto-combustion.

Soft Chemistry Routes for the Synthesis of Sr

Niobates and tantalates of rare-earth compounds are high temperature proton conductor (HTCP) oxides that are gaining attention as possible stable electrolyte materials for application in intermediate temperature solid oxide fuel cells (IT-SOFCs). Sr0.02La0.98Nb0.6Ta0.4O4 was synthesized by auto-combustion and co-precipitation routes, and by solid state reaction for sake of comparison, expecting an improvement in conductivity for the wet chemistry routes over the conventional solid state reaction method. Single phase materials were obtained at 1100°C by autocombustion and by co-precipitation. The synthesized powders were characterized by X-ray diffraction (XRD) and dilatometric analyses. Dense electrolytes were obtained by pressing the calcined powders into cylindrical pellets and then sintering at 1600°C for 10 h. The pellets were observed by scanning electron microscopy (SEM). Electrical conductivity of the sintered pellets was measured as a function of the temperature by electrochemical impedance spectroscopy (EIS) measurements. Proton conductivity of 2.2×10-4 S cm-1 was obtained in wet argon atmosphere at 800°C for the sample produced via auto-combustion.