Transfer function analysis of the direct methanol fuel cells response to dynamic changes in cell current

This paper presents investigations on the dynamic behaviour of direct methanol fuel cells (DMFCs). Experimental cell voltage responses to cell current step changes are investigated with transfer function analysis. The voltage response shows significant overshooting behaviour (up to 80 %) in most places when applying cell current steps to the DMFC. Linear system analysis is applied to a set of dynamic models with different complexity, and a criterion for cell voltage overshooting is given. In the models, the dominating physico-chemical phenomenon is the transport of methanol through the membrane, causing cathodic overpotential overshooting. This is supported by experimental observations. Moreover, the models can be suitable for controller design