DESIGN AND OPTIMIZATION OF MIXED IONIC-ELECTRONIC CONDUCTIVE MATERIAL FOR USE IN SOLID OXIDE FUEL CELL UTILIZING CARBON NANOTUBES

Abstract

Triple phase boundary (TPB) is considered to be an important limiting factor of the fuel cell performance. Triple phase boundary is a geometrical line where the ionic, electronic and gaseous fuel phase of the fuel cell comes in contact. Electrochemical reactions of the fuel cell occur at the TPB sites. The TPB length greatly impacts the efficiency of the fuel cells. Carbon nanotubes have recently been shown to enhance oxygen reduction reaction (ORR) of the fuel cell and transfer electrons with its conductive properties. CNT also provides porosity in the electrode and could facilitate mass transport. CNT allows for oxygen and gas to permeate inside it to reach reaction sites. This research theorizes a new model for the electrode material. This model utilizes CNT as the electronic phase and YSZ as the ionic phase. The two phases are mixed together to form a new kind of mixed ionic-electronic conductive (MIEC) material. MIEC allows for the electrode to be electronic and ionic conductive. MIEC allows for a denser TPB site throughout the electrode when compared to the traditional electrode. In traditional electrode TPB sites are only present at the interface of electrode and electrolyte. A mathematical model is developed for this new material to calculate volumetric TPB length using geometrical values of the electrode. Different parameters are taken into account such as porosity, particle radius, CNT diameter, contact ratio of two phases, the distance between ionic particles and distance between CNT and particle. Graphs are produced to get a better understanding of the trends of TPB length when different parameters are altered.