Solid oxide fuel cell (SOFC) is a high temperature fuel cell operating between 650oC-1000oC with increasing importance for stationary power house applications. High reactivity, comparatively inexpensive anode and cathode material, high power density, high level of usable heat and the possibility of using flexible fuels have made SOFC an attractive choice for utility and industrial applications.

In a tubular solid oxide fuel cell, as the size of the gas flow channels are increased for a given circumferential area, the velocity of the gaseous species decrease. This results in a higher residence time for the reactants thereby increasing the percentage conversion of the reactants. On the other hand, an increase in size leads to a reduction in the pressure drop across the cell. For a given exit pressure, this results in a reduced pressure inside the cell. The decrease in the pressure reduces the molar concentration of the reactants at a given temperature affecting the conversion of the reactants and increasing the concentration overpotential of the cell. Therefore an optimum L/D ratio exists for a given circumferential area. A detailed two dimensional steady state model is developed for the optimization of the aspect ratio for a set of given materials and operating conditions. In another optimization study, a graded loading of Ni at the anode is considered with the objective of reducing the temperature gradient across the cell. In a traditional SOFC, Ni loading in the Ni-YSZ anode remains uniform. If the Ni-loading near the channel is reduced, the diffusion length of the gaseous species will increase resulting in a higher concentration overpotential and a more pronounced temperature gradient towards the anode TPB. In contrast, a higher loading of Ni near the channel will result in a higher overall ohmic resistance of the cell and steeper temperature gradient near the channel. Computational optimization studies on optimal loading of Ni in the Ni-YSZ anode for the minimization of the temperature gradients will be presented in this talk.

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