Electrochemical characterisation of fuel cell stack during cold start

Abstract

Fuel cell self start at negative temperature conditions is not an easy task due to the water produced by the reduction of oxygen at the cathode. This amount of water can turn into ice and block the reaction before the temperature inside the fuel cell reaches positive values. The mechanism of the physical process which leads to oxidant starvation phenomena when ice appears is not yet well identified. In order to obtain a deeper understanding of this problem, the article presents some experimental investigations conducted on a short fuel cell stack. These experiments simulate vehicle technology operated in cold start conditions not with the primary objective to reach a successful and rapid start-up but much rather to characterise and understand the cold start phenomena until starvation occurs. A number of polarisation curves, electrochemical spectroscopy and cyclic voltammetry measurements are done on the stack before, after and also during the cold starts experiments. It is observed that the process of drying and cooling down prior to cold start have a great impact on the electrochemical cathode area. The results obtained show the evolution of the stack behaviour during the low temperature operation with a slow production of frost. The consequence on the individual cells in terms of inhomogeneous degradation is highlighted.