Negative differential resistance and steady state multiplicity in solid oxide fuel cells

Abstract

Nonlinear dynamics play a vital role in electrochemical systems and there are many examples in the literature of systems which exhibit interesting behaviour such as multiple steady states and autonomous oscillations. Within the fuel cell community nonlinear dynamics of proton exchange membrane fuel cells have been studied in depth, however other types of fuel cell have not received nearly as much attention. Since fuel cell systems are characterised by a wide variety of physicochemical processes operating on multiple time scales, it is crucial that the nonlinear effects are understood in order to better design and operate them. This work presents the first experimental results on global negative differential resistance and steady state multiplicity in solid oxide fuel cells operating on hydrogen under high fuel utilisation, alongside a basic prototype model that has been adapted from the literature in order to explore the origins of this behaviour. Results are discussed within the context of theoretical predictions from the literature and the prototype model presented within.