Effect of anodic concentration overvoltage on power generation characteristics of solid oxide fuel cells

Current-voltage (I-V) and anodic polarization characteristics were measured for the H-2-fueled solid oxide fuel cell with an 8 mole percent yttria-stabilized zirconia (YSZ) electrolyte and Ni YSZ anode. For a H-2-rich H-2-H2O system, the I-V curve was characterized by a high open-circuit voltage and significant concave bending in the small cut-rent density region. For an extremely dilute fuel condition, the curve started from a straight decrease of the voltage followed by a sharp voltage drop due to Limiting current. Significant contribution of concentration overvoltage was suggested in determining the fuel systems. The experimentally obtained mining the shape of the I-V curve from the calculated equilibrium P(O2)in the fuel systems. The experimentally obtained anodic polarization curve could be fitted to the calculated curve based on the concentration difference across the Ni-YSZ anode layer. The effective diffusion coefficient, D-eff, of the Ni-YSZ cermet which affects the anodic polarization, is estimated to be 10(-2) to 10(-1) cm(2) s(-1). The electrode polarization conductivity, sigma(a), was maximum at P-O2 = ca. 10(-8) Pa, and decreased with increasing or decreasing P-O2. This behavior could be explained by considering the concentration over-voltage based on the relation between log P-O2 and the fractional concentration of H-2.