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In this paper we investigate the oscillatory response of a methane fuelled solid oxide fuel cell (SOFC) under weakly humidified conditions. We present experimental results conducted using operating conditions which allow for direct comparison with the mathematical model presented in Sands et al. 2014. We find transitions from a stable, steady current producing state, to nonlinear autonomous oscillations, to a zero current output state, which corresponds to the pattern of behavior also observed in the model. In this paper we briefly summarize the model from Sands et al. 2014, followed by a description of the cell assembly and experimental procedures. The results are then presented, followed by a discussion and comparison with the model. [ABSTRACT FROM AUTHOR]

In this article, we address the phenomenon of temporal, self-sustained oscillations for a solid oxide fuel cell which utilises a humidified methane fuel stream. Our objective is to uncover the fundamental mechanisms giving rise to current oscillations that have been observed experimentally. To this end, we develop a model based on the fundamental chemical kinetics and transfer processes which take place within the fuel cell. This leads to a three-dimensional dynamical system, which, under typical operating conditions, is rationally reducible to a planar dynamical system. This planar dynamical system was studied in (Sands et al., Proc. R. Soc. Lond. A 470 (2014)) for the case where the parameter ¯c0 ⪡ 1, corresponding with a weakly humidified fuel stream. In the present article, the structural dynamics of the planar dynamical system for the case where the parameter ¯c0 = O(1), which corresponds with a humidified fuel stream, are studied in detail. Self-sustained oscillations are shown to arise through Hopf bifurcations in this planar dynamical system, and the key parameter ranges for the occurrence of such oscillations are identified. Fuel stream humidification is also shown to significantly alter the fuel cell dynamics, leading to hysteresis. [ABSTRACT FROM AUTHOR]