Intrinsic methane steam reforming kinetics on nickel-ceria solid oxide fuel cell anodes

Abstract

Direct internal reforming in solid oxide fuel cells (SOFCs) is advantageous as it enables to heat and steam from the exothermic hydrogen oxidation reaction in the endothermic steam reforming reaction. However, it may increase potentially deteriorating temperature gradients as well. The temperature and concentration profiles can be accurately simulated with adequate SOFC models and intrinsic methane steam reforming (MSR) kinetics. Therefore, this study aims to derive intrinsic MSR kinetics suitable for control-oriented dynamic SOFC models. The individual influences of the methane, steam and hydrogen partial pressures on the MSR reaction are experimentally studied on functional electrolyte supported cells with nickel-gadolinium doped cerium anodes. A non-proportional dependence of the MSR rate on the methane partial pressure and a slight negative dependence on the steam partial pressure are observed, but the effect of the hydrogen partial pressure seems insignificant. Various kinetic rate equations are parameterised with the experimental data and an ideal plug flow reactor model. An intrinsic Langmuir-Hinshelwood mechanism for a rate determining step between associatively adsorbed methane and dissociatively adsorbed steam on the catalyst surface shows good agreement with the experimental data, and is thermodynamically and physically consistent.