Ammonia fueled Proton conducting devices: toward more and more sustainable energy conversion and storage
Résumé
This contribution describes the development of proton-conductive solid oxide fuel cells, in which ammonia is the fuel. Not presenting carbon, ammonia offers the possibility of sustainable development in "carbon free" perspective. Ammonia is an interesting energy carrier being characterized by good hydrogen content; it is highly studied and produced with a well-established process. Proton conductor based solid oxide cells can operate at much lower temperatures (500-600°C) compared to the traditional solid oxide cells (800-1000°C). The necessity of developing proton based devices working with fuel ammonia can answer to the desire of low cost and high safety. Electrochemically active anodes active with this fuel, pushed the research in the design and optimization of this component. A Nickel-Yttrium-doped Barium cerate (Ni-BCY) cermet is developed and oxidized in this contribution; the addition of Nickel, by impregnation, catalyzes the decomposition reaction of ammonia and increases the electric conductivity. The chosen electrolyte is Y-doped Barium cerate (BCY); the use of ammonia as fuel allows to avoid the weakness of this materials: the reactivity with acidic gases as CO2. La-Sr-Co ferrite (LSCF) has been chosen for cathode. LSCF is a mixed ionic/electronic conductor which has been proposed as a valid cathode material thanks to its high oxygen diffusivity. Electrode and electrolyte have been characterized by XPS, XRD, SEM/EDX, BET, TPR, TPO; the symmetrical cells with BCY as electrolyte and Ni-BCY as electrodes were tested, at first, in a single chamber design, to analyze the electrochemical performances under different conditions, between 550 and 750°C. The measurements were carried out both in single and double chamber design. The results are encouraging: comparable results have been obtained in hydrogen and ammonia, confirming the success in the cell fueled with ammonia and the possibility to use this safety fuel as energy storage and hydrogen vector.