Effect of total pressure difference on counter transport of gases with different molecular weights through solid oxide fuel cell anode

The counter transport of gases with different molecular weights is experimentally and numerically investigated to clarify gas transport phenomena of a hydrogen-steam binary mixture in a solid oxide fuel cell (SOFC) anode during operation. The crossover fluxes through the anodes with different porous microstructures are measured and the effect of total pressure difference on the counter gas transport is evaluated. Without the total pressure difference, an imbalance is found in the diffusion fluxes of gases with different molecular weights in accordance with Graham's diffusion law. Therefore, for the equimolar transport, a total pressure difference is required to enhance the transport of the gas with a larger molecular weight. A numerical model based on the cylindrical pore interpolation model (CPIM) is developed and confirmed to be able to reproduce the experimental results accurately. In addition, the limiting current density of an SOFC predicted using the model we developed agrees with that of the cell evaluated in the experiment. The total pressure at the anode-electrolyte interface is found to be about 20 kPa higher than that on the anode surface at 1 A cm-2, which is non-negligible. Therefore, we must take this into account when we perform numerical simulation of anode-supported SOFCs.