Modelling Of The Electrochemical Conduction Of Different Types Of Partially Sintered Fuel Cell Electrodes By Discrete Simulations

• Main Authors: Schneider, L C R, Martin, C L, Bouvard, D, Bultel, Y
• Format: Conference Proceeding
• Language: English
• ISSN: 0094-243X
• DOI: 10.1063/1.3180039

Composite electrodes for Solid Oxide Fuel Cells (SOFC) are generally obtained through partial sintering of a mixture of ionic and electronic conducting powders. Enhancing the electrochemical performances of SOFC electrodes requires the multiplication of so-called Triple Phase Boundary points (where the gas and the ionic and electronic conducting materials meet), some residual porosity, and the percolation of the two particle networks (ionic and electronic). Also, the poor intrinsic conductivity of ionic particles requires the reinforcement of the ionic network. Thus, the optimization of the electrode microstructure is a complex task and must take into account the particulate nature of the partially sintered material of the electrode. We propose to model the electrode material as a 3D packing of spheres, which sintering is simulated by the Discrete Element Method (DEM). This allows the generation of a realistic numerical microstructure for which the geometric features of each contact is known. Typically we generate electrodes with 40 000 spherical particles and residual porosity of 25%. For the determination of the electrochemical performance, the packing is sandwiched between a current collector and an electrolyte. The packing is then replaced by a network of electronic, ionic and electrochemical resistances, and the effective conductivity of the electrode is calculated. Our simulations allow the importance of percolation effects to be demonstrated. We also compute the effective conductivity of composition graded electrodes and compare them to non-graded composite electrodes. We show that only slightly graded electrodes can compete with non-graded composite electrodes. In any case, the simulations show that due to percolation problems, one should not expect large gains in terms of electrochemical performance when grading electrodes. Instead, we propose a new and more effective microstructural architecture for which the electronic network percolation is imposed.