PNNL

Abstract

Internal reforming of hydrocarbon fuels (e.g. methane or natural gas) can improve the thermal efficiency of solid oxide fuel cells (SOFC) by balancing exothermic electrochemical oxidation of H2 and CO at the anode/cathode interface with endothermic steam reforming reactions on the anode1. Generally the rate of reforming is much greater than the rate of H2 and CO oxidation leading to extensive thermal gradients across the cell that can compromise the physical integrity of the cell. Therefore, methods to control reformation activity and predict thermal gradients are needed. Computational modeling is used to predict thermal gradients and fuel conversion profiles across the cell, thus accurate and predictable methane reforming kinetics are required. Significant discrepancies in activation energy, rate expressions, and rate constants for methane reforming over nickel-yttria stabilized zirconia (Ni-YSZ) are reported in the open literature1-4. The objective of this work is to provide clarity on factors leading to discrepancies in kinetic information reported in the literature and identify potential methods to control reforming rates over NiYSZ anodes. Effects of pretreatment and reforming on Ni microstructure and activity of NiYSZ anodes for methane reforming were examined under open-circuit conditions.