Enrico Traversa

Preparation of sol-gel nano-composites containing copper oxide and their gas sensing properties

Sol-gel derived composite materials were prepared with nano-sized copper particles in silica matrix. Nano-sized oxide coatings were grown on the nano-particles of copper by subjecting the composites to a controlled oxidation treatment at different temperatures. The current response of samples with oxide layers of different thickness were studied at fixed temperatures in the range 350–450°C in the presence of different concentrations of CO and NO2. The nano-composites were sensitive to both the gases. The operating temperature and the oxide thickness were found to have significant effect on the sensing properties.

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.

Non-Nernstian Planar Sensors Based on YSZ with an Nb2O5 Electrode: Discussion on Sensing Mechanism

Solid electrolyte based sensors have been widely studied for the detection of CO/HC and NOx at high temperature. Nevertheless, the discussion about the sensing mechanism of non-nernstian electrochemical gas sensors, with a semiconducting sensing electrode, is still open. In this work, a study of the influence of the metallic electrode under the semiconducting metal oxide Nb2O5 on the sensor response was performed. Planar sensors based on tape-cast YSZ layers were fabricated. Two Pt or Au finger electrodes were deposited in a parallel arrangement on a single side of YSZ. One of these electrodes was covered with Nb2O5 thick film. In order to better understand the sensing mechanism, the electrical measurements were correlated with catalytic measurements performed on both sensing and reference electrodes.

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.

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.

Electrical properties of sol-gel processed hybrid films

We report on the electrical properties of a hybrid organic/inorganic material synthesized by a sol-gel technique. Spin-coated films with sputtered Nb electrodes in a sandwich-type geometry were studied by a.c. measurements. The aging of the films affected the resistance of the samples. Electrochemical impedance spectroscopy (EIS) measurements were performed in a test chamber at different relative humidity (RH) values to evaluate the aging mechanism.

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.

Performance of Solid Oxide Fuel Cells with In-Doped BaZrO3 Electrolyte Films on Different Anode Substrates

High temperature proton conductors received broad interests because they show high ionic conductivities and low activation energies, and provide an alternative solution for SOFC electrolyte materials compared with oxygen-ion conductors. Although many oxides have been found to show certain protonic conductivity at high temperatures, the most widely studies high temperature proton conductors are still doped BaCeO3 and doped BaZrO3 systems. In the view of practical applications, the poor chemical of BaCeO3 limits its application, whereas BaZrO3 is regarded as a good electrolyte candidate because of its excellent chemical stability and high bulk conductivity. 4 However, the poor sinteractivity and low grain boundary conductivity of BaZrO3 hinder its applications. In addition, current reports for the fuel cells based on BaZrO3 electrolyte usually shows undesirable performance because of its refractory nature.