Performance Improvement by Temperature Control of an Open-Cathode PEM Fuel Cell System

The work presented in this article combines experimental analysis and theoretical studies of temperature effects on the performance of an open-cathode, self-humidified PEM fuel cell system for the design of optimal control strategies. The experimental analysis shows the great potential of improving the system performance by proper thermal management. The most significant temperature dependent parameter of the system under study is the exchange current density. On the one hand it is influenced positively by a temperature increase as this lowers the activation barrier. On the other hand a higher temperature causes a reduction of the electrochemical active sites in the cathode catalyst layer due to lower water content in the ionomer and primary pores. Dynamic models for fuel cell temperature, liquid water transport and the related electrochemistry have been developed and validated against the experiment. A cascaded Extremum Seeking control algorithm with a local PI controller is proposed to regulate the temperature to a fuel cell voltage maximum. However, the slow dynamics of the temperature related catalyst-drying effect on performance complicate the optimal thermal management with model-free control strategies.