Modeling of the Kinetic Factors in Flame-Assisted Fuel Cells

Abstract

Despite the significant experimental work in flame-assisted fuel cells (FFCs), a detailed model of FFC polarization losses does not exist in the literature. This paper thus presents a combination of theoretical and empirical models to describe the performance of FFCs. Previous models for solid oxide fuel cell (SOFC) polarization losses typically assumed values of the charge transfer coefficient (α) of 0.5 and a Nernst diffusion layer thickness (δ) equal to the anode thickness. The theoretical model developed in this work, parametrized in α and δ, is empirically fitted to the experimental polarization curves to understand the variation of these parameters while the FFC operates with different fuel partial pressures. Model results indicate that at low fuel concentrations (CR,0), the current density of the fuel cell (j) is limited by mass transfer limitations. As CR,0 increases, j is then limited by activation due to the limited number of activation sites in the fuel cell. Activation loss (ɳact) remains constant at low CR,0 (concentration limited) and increases rapidly with an increase in CR,0 under activation-limited conditions. The value of α, which varies significantly from 0.5, under concentration-limited conditions remains constant at ~0.24 and decreases rapidly with CR,0 under activation-limited conditions. The value of δ, which is much smaller than anode thickness, remains constant at ~10 µm under concentration-limited conditions and increases to a constant value of ~17.5 µm under activation limitations. Overcoming activation losses under high CR,0 conditions requires further investigation of FFCs.