Understanding the dynamic behaviour of direct methanol fuel cells: Response to step changes in cell current

This paper presents investigations on the dynamic behaviour of Direct Methanol Fuel Cells (DMFC). Experimental cell voltage responses to step changes in cell current are analysed. Nonlinear DMFC models indicate that the anode reaction mechanism is the main physico-chemical phenomenon which causes anode overpotential overshooting, hence cell voltage overshooting. Since the models are strongly nonlinear, linearised models underestimate the DMFC’s dynamic behaviour. The presented models correctly predict the influence of operating conditions like current density level and current step size on the cell voltage response. Furthermore, the models indicate a low influence of the methanol distribution inside flow fields: Distribution has an influence on the cell voltage only in cells with very low local methanol concentrations (<0.1 M).