Thermo-electrochemical modeling of oxygen ion-conducting solid oxide fuel cells with internal steam reforming in the water-energy nexus

Abstract

The precise estimation of chemical equilibrium state is highly crucial when simulating electrochemical and thermodynamic aspects of oxygen ion-conducting solid oxide fuel cells (SOFC). One way to determine the equilibrium state of an internal reforming solid oxide fuel cell system is to compute the total Gibbs free energy of the system (G) and then, adjust the molar amounts of each substance, subject to element balances, so as to minimize G. Multi-dimensional optimization algorithms can be used for this purpose. In this paper, a powerful analytical solution method called Lagrange's method of undetermined multipliers is used for estimating the chemical equilibrium state. The effects of each current density, reaction temperature and pressure of the stack, and fuel and carbon dioxide utilization ratios on the voltage losses and output voltage and power of the stack, efficiency, and molar portions of the exhaust chemical species in anode and cathode, are investigated. The solid oxide fuel cell stack simulations by Lagrange's method at a definite state shows an efficiency of 54.6% and output power of 158.3 kW.