A model for SOFC anode performance

A model for anode performance of a planar anode-supported SOFC is developed. The model includes Butler-Volmer relation for the hydrogen oxidation, Ohm's law for ionic current and equation of hydrogen mass balance in the anode channel. We show that the regime of anode operation depends on the relation between the cell current density j and the critical current density j(crit). Analytical solutions to the system of governing equations for the case of "low" (j<j(crit)) and "high" (j >> j(crit)) currents are derived. In the "low-current" regime the anode polarization voltage is proportional to cell current, which justifies the notion of anodic activation resistivity R(a). Full hydrogen utilization increases the value of R(a) by a factor of 2. In the "high-current" regime polarization voltage depends on cell current logarithmically. with the effective Tafel slope being twice the kinetic value (doubling of Tafel slope). In this regime 100% hydrogen utilization leads to a constant similar or equal to 230-mV shift of polarization curve as a whole. (C) 2009 Elsevier Ltd. All rights reserved.