Meyer, QP-G; (2015) Advanced Diagnostics for Air-Cooled, Open-Cathode Polymer Electrolyte Fuel Cells. Doctoral thesis , UCL (University College London).

Abstract

Polymer electrolyte fuel cells (PEFCs) operating on hydrogen offer the possibility of zero-emission electricity generation. The technology has shown significant advances in terms of performance and durability, and wide-scale commercialisation in a range of applications is imminent. However, technological challenges still exist and the ability to understand the internal workings of fuel cells during operation is one of the most powerful ways to tackle these issues. This work presents advanced diagnosis on air-cooled, open-cathode state-of-the-art polymer electrolyte membrane fuel cells. One of the main challenges in understanding and improving the performance of air-cooled open-cathode fuel cells is the fact that reactant supply to the cathode is linked to air supply for cooling. As such, the electro-thermal properties of this class of fuel cell must be considered in order to optimise operation. Firstly, the intricate relationship between the temperature, voltage, current density and air and cooling flow rate is investigated, in order to determine the optimum electro-thermal regime of operation. Electrochemical impedance spectroscopy enables the determination of the ‘current of lowest resistance’, as a function of the system parameters. In conjunction, current and temperature mapping reveals insights on the in-situ gradients, and their correlations with the voltage decay at high current density and limiting reactant flow rate. Finally, an optimisation of the operation is proposed at the cell and system level, minimising the resistive losses and parasitic power losses. This work also investigates the processes occurring in dead-ended and through-flow at the anode. This investigation combines thermal imaging, off-gas analysis and a novel reconstructive electrochemical impedance spectroscopy methodology, enabling the effects of nitrogen accumulation and water flooding on cell performance to be separated. Significant temperature and current density gradients are revealed in dead-ended mode, which suggest localised flooding and localised dehydration.

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