Effects of gradient porosity and gradient particle on performances of planar SOFCs

A comprehensive 3-D single-unit cell model is established to study the performance of anode-supported solid oxide fuel cells (SOFCs) with gradient porosity and gradient particle size anodes. The coupled phenomena of fluid flow, multi-component mass transfer, electron/ion transport and electrochemical reactions in the SOFC are numerically simulated. Effects of the gradient porosity and gradient particle size distributions on the cell mass transfer and electrical performances are investigated. Results reveal that the positive effects of high porosity gradient on the activation and concentration overpotentials are nearly equal to the negative effect on the ohmic overpotential, and therefore the electrical performances of the three gradient porosity distributions almost remain the same. High porosity gradient is beneficial to enhance the mass transfer performance of SOFC; however, it is not advantageous to the electrical performance improvement. The SOFC with high particle size gradient could considerably reduce the ohmic overpotential, which accounts for a large share of the three polarization losses. Influence of the particle size gradient is more effective than that of the porosity gradient on the cell performances. These results are helpful to the high performance design of the anode-supported planar SOFC.