Proton and Mixed Conductors for Dual Membrane Fuel Cells
- PDF / 1,056,202 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 67 Downloads / 230 Views
Proton and Mixed Conductors for Dual Membrane Fuel Cells Massimo Viviani1, Sabrina Presto1, Antonio Barbucci2,1, Maria P. Carpanese1,2, Roberta Amendola1, Alain S. Thorel3, Anthony Chesnaud3, Joao Abreu3, Remi Costa4,3, Zeynep Ilhan4, Sayed-Asif Ansar4,Daria E. Vladikova5 and Zdravko B. Stoynov5 1
Institute for Energetics and Interphases, CNR, Via De Marini 6, 16149 Genova, Italy
2
DiCheP, University of Genoa, P. le Kennedy 1, 16129 Genova, Italy
3
Centre Matériaux, Mines-ParisTech, BP87, Evry Cedex 91003, France.
4
German Aerospace Center (DLR-ITT), Pfaffenwaldring 38-40, Stuttgart D-70569, Germany
5
Institute of Electrochemistry and Energy Systems-BAS, 10 Acad. G. Bonchev, 1113 Sofia, Bulgaria ABSTRACT This paper presents results for the conductivity of BaCe0.85Y0.15O2-δ (BCY15) measured by electrochemical impedance spectroscopy in wet hydrogen and in Air, as well as test results from the application of the material in a new dual membrane fuel cell configuration (“IDEAL Cell”), in which the water is produced and evacuated through a separate chamber. The conductivity of dense BCY15 in wet hydrogen atmosphere at 700 °C is 2.0 10-2 S/cm. The measured values in air are of the same order. Preliminary tests of the material in the new cell design, where the three types of conductivity (protonic, oxide ion and mixed) are used in different cell compartments, are successfully performed. INTRODUCTION The measurement of high temperature proton conductivity in doped Sr and Ba cerates in the late eighties of the last century [1,2] opened a new niche for optimization of SOFC towards reduction of the operating temperature (500-800 °C) due to the higher mobility of protons. In proton conducting SOFC (pSOFC) the water vapor is evacuated through the cathode where it mixes with the excess air and thus does not influence the cell voltage [3-6]. Acceptor doped perovskites with general formula AB1-xMxO3-α (A = Ba, Sr; B = Ce, Zr; M = rare earth metal; x less than the upper limit of solid solution formation) are promising proton conducting systems. Proton conduction increases in the order BaCeO3 > SrCeO3 > SrZrO3, while the chemical stability deteriorates in the opposite order [6,7]. Under humidified hydrogen atmosphere protonic defects are formed by dissociative absorption of water in the presence of oxygen vacancies. Water vapor dissociates into a hydroxide ion which fills an oxide-ion vacancy, and a proton that forms a covalent bond with lattice oxygen, i.e. two proton defects are created stoichiometrically [8]:
H 2O(g) + VO•• + OOx → 2OH •O
(1)
Since the incorporation of water is exothermic [6,10], the protonic transport is dominating at lower temperatures (under 600 °C). The doping with aliovalent rare earth cations causes the formation of oxygen vacancies and significantly improves the proton conductivity [4-8]. In the BaCeO3 system, which is considered to be very promising because of the measured high protonic conductivity (0.01 – 0.05 S/cm between 600-800 °C [9,10]), the reaction can be described as: x 2Ce Ce + M 2O3
Data Loading...
