Tuning transport mechanisms in fuel-assisted solid oxide electrolysis cells for enhanced performance and product selectivity: Thermodynamic and kinetic modeling

Abstract

Fuel-assisted solid oxide electrolysis cells (FASOECs) have the capacity to generate power and valuable chemicals, simultaneously, by supplying fuels including methane, carbon monoxide, and hydrogen to a cell’s anode. Such fuels can comprise the tail gas of Fischer–Tropsch (FT) reactors and can be further exploited by FASOECs to reduce the amount of energy required to facilitate steam electrolysis. Important challenges that remain in the development of FASOECs, however, are determining the reactions that contribute to the transport phenomena of the system and how they influence the performance of these devices. To date, most numerical models of FASOECs have accounted for methane steam reforming and the water gas shift reaction in the anode, which cannot predict the onset of carbon deposition and other reactions that can occur in different regions of a cell. For the first time, a combined mass and heat transport model of an FASOEC fed with a multi-component fuel mixture is constructed to track the reaction pathways by which each component is utilized/produced and to develop strategies to enhance their performance and product selectivity. We reveal the transport regimes (and corresponding cell specifications) in which carbon deposition can be alleviated, which has been observed in previous experiments on methane-assisted solid oxide cells, and those that yield H2/CO ratios desirable for the feedstock of FT reactors. As a result of this framework, designers will have an understanding of how to select appropriate values of the design specifications and operating conditions of FASOECs, in order to augment their efficiency and product selectivity, while mitigating carbon deposition.