Abstract:
The architecture of Solid Oxide fuel Cells/Solid Oxide Electrolysis Cells (SOFC/SOEC) has changed with time, mainly with regard to the operating temperature. Decreasing this temperature from 950°C down to 600°C required not only to decrease the ohmic drop of the electrolyte, but also to enhance the electrode performances. If the classical hydrogen electrode remains the efficient Ni/electrolyte cermet, the oxygen electrode has to be significantly improved with the aim to reduce the overpotential.
Early oxygen electrodes in ESC (Electrolyte Supported Cell operating at T > 900°C) were made of a screen printed YSZ (Yttria Stabilized Zirconia) - LSM (Lanthanum Strontium Manganite) composite. Later on, these composite electrodes were replaced in ASC (Anode Supported Cells operating at about 750°C) by appropriate unique oxides showing mixed ionic and electronic conduction, such as the Lanthanum Strontium Ferro-Cobaltite (LSFC) [1].
More recently, we have shown that lanthanide nickelates Ln2NiO4+δ (Ln = La, Pr or Nd) exhibit very good ionic diffusivity of oxides ions as well as oxygen exchange properties leading to outstanding electrochemical properties as oxygen electrode materials [1-2].
Improvement of the cell performance was also achieved thanks to the addition of a thin interlayer ( = 2-3 µm) in between the electrolyte and the oxygen electrode; it mainly plays the role of a barrier against cation diffusion due to the reactivity of these materials with each other [3].
In the last generation of cells, the so called MSC (Metal Supported Cell operating at 600-700°C), has to allow imagination of new ways to make the oxygen electrodes. This has to be done with regard to the presence of metal which can be oxidized at temperatures higher than 900°C during the fabrication process. The infiltration technique has proven to be a promising route to make highly efficient electrodes [4]. The electrocatalyst is infiltrated in a porous skeleton (Gadolinia doped Ceria, GDC) sintered on the YSZ electrolyte, then fired at low temperatures (T = 600-800°C), leading to the formation of nanoparticles showing high electrocatalytic properties [5].
A review of all these issues is presented.
References:[1] J.-C. Grenier, J.-M. Bassat, F. Mauvy, Functional materials for sustainable energy applications, eds. J. A. Kilner, S. J. Skinner, S. J. C. Irvine and P. P. Edwards, Woodhead Publishing 402-444 (2012)
[2] Ogier T., Mauvy F., Bassat J. M., Laurencin J., Mougin J. and Grenier J.-C. Int. J. Hydrogen Energy, 40(46) 2015, 15885-15892.
|3] A. Flura, C. Nicollet, B. Zeimetz, V. Vibhu, A. Rougier, J.-M. Bassat, J.-C. Grenier, Int. J. Electrochemical Soc. 163(6) (2016) F523-F532.
[4] J. Vohs, R. Gorte, Adv. Mater., 21, 943-956 (2009).
[5] C. Nicollet, A. Flura, V. Vibhu, A. Rougier, J.-M. Bassat, J.-C. Grenier, Intern. J. Hydrogen Energy, 41(34), 15538-15544 (2016).
|
