Sabrina Presto

IDEAL-Cell, Innovative Dual mEmbrAne fueL-Cell: Fabrication and Electrochemical Testing of First Prototypes

The IDEAL-Cell concept is based on the junction between a PCFC anode/electrolyte section and a SOFC cathode/electrolyte section, through a mixed proton and oxide ion conducting porous ceramic membrane, operating in the temperature range 600-700°C. Recombination of ions takes place within the junction, or central membrane (CM), and water vapor is evacuated through open porosity. The first results on the fabrication of multilayered samples reproducing the IDEAL-Cell structure are reported here, together with electrochemical tests carried out on selected samples in order to evaluate the performances of the chosen materials and to demonstrate the feasibility of this innovative concept of fuel cell.

Ionic conductivity and local structural features in Ce1-xSmxO2-x/2

Sm-Doped ceria is one of the most promising materials to be used as electrolyte in solid oxide fuel cells due to its remarkable ionic conductivity values in the intermediate temperature range. Transport properties and local structural features of Ce1-xSmxO2-x/2 (0.1 ≤ x ≤ 0.7) were studied by an impedance/μ-Raman spectroscopy coupled approach up to 1073 K. Results suggest that C-based nanosized defect clusters are responsible for the drop in ionic conductivity observed even at x = 0.2, i.e. at a Sm content lower than necessary to allow C domains to reach the percolation threshold through crystallites. Moreover, within the fluorite-type compositional region, with increasing the Sm content, defect clusters undergo a rearrangement resulting in the enlargement of C-based domains rather than in the increase of their number; at higher x, on the contrary, both the size and amount of C domains increase in parallel.

Infiltration of Metal Substrates with Nanostructured CeO2 by a Room-Temperature Wet Process.

A room-temperature infiltration procedure for the deposition of CeO2 nanopowders on Ni-based foams employing stable CeO2 suspensions in water has been developed. It consists of a two-steps dipping process, the first in nanopowder suspension at pH 6.5 followed by further dipping into a NH3OH solution at pH 12. The pH shift represents a key factor to improve the homogeneity and dispersion of infiltrated powder by avoiding coalescence during the drying step. Water-based suspensions have been prepared starting from a commercial nanostructured CeO2. Powder was characterized by X-ray diffraction, particle size and specific surface area measurements, transmission electron microscopy. Stability of suspensions was studied by zeta potential measurements at low concentration, while sedimentation tests were carried out on highly concentrated suspensions as a function of pH, CeO2 amount and surfactant presence. Effect of CeO2 concentration, surfactant addition, pH value, substrate composition and microstructure were taken in account. Under best conditions, very homogeneous infiltrations could be obtained without any preferential orientation or agglomerates. Thermal stability of the composites infiltrated materials was also tested. The technique seems to be very promising in advanced nanostructured decorations and coating preparation.

Electrochemical Performances of a Reversible High Temperature Fuel Cell Based on a Mixed Anionic-Protonic Conductor

This paper deals with the fabrication and study of a high temperature solid electrolyte supporting electrochemical cell operating as SOFC and SOEC. The cell is based on the idea of a dual membrane electrolyte, which has the advantage to separate the cell in three different chambers: hydrogen side, oxygen side and dual membrane (D.M.), where water production-SOFC or splitting-SOEC takes place. The tape casted supporting electrolyte is constituted by a dense/porous/dense tri-layer, made of BaCe0.85Y0.15O3-δ (BCY), which is a mixed ionic conductor. The electrolyte sandwich was formed by in-situ sintering of stacked green tapes with or without pore former. The process optimization (slurry formulation, lamination and thermal treatments) led to flat, crack-free, 580 µm thick BCY discs with a well-controlled microstructure. Platinum electrodes were deposited on both sides of the sandwich-structured electrolyte. The cell was then electrochemically studied under different operating conditions of temperature, overpotentials and gas feeding, either in SOFC and SOEC mode. From the presented results it can be highlighted that despite the dense electrolyte layers were kept thick and the electrodes were made of platinum, the electrochemical study of the cell show: i) a promising power density, ii) an interesting reversibility SOFC/SOEC, iii) a proved splitting of the water contained in the porous central membrane when the cell operates as an electrolyser (SOEC). Degradation of the cell performance is also focused.

Towards Understanding the Dual Membrane Fuel Cell (IDEAL-Cell) Using a Metallic Central Membrane

This work presents results of a measurement setup which was constructed for understanding the performance contributions of the individual compartments and reactions taking place in the patented concept of IDEAL-Cell (described in detail in(1)). By inserting a third measurement point at the central membrane of an ideal cell it was possible to measure the cell in three different modes corresponding to hydrogen, oxygen compartment and the full cell. Recorded maximum power densities of (~4, ~7, 11, 16) mW/cm² at (600, 650, 700, 750) °C in H2-O2 atmosphere respectively were observed which were similar to the values of proof of concept ideal cell samples tested so far. Moreover in this setup it was possible to record higher maximum power densities for the hydrogen (proton conducting) compartment which was (~14, 22, 33*, ~38*) mW/cm² at (600, 650, 700, 750) °C.