The ability of the polymer electrolyte fuel cell to start up at sub-freezing temperatures, also called cold start, is paramount for its transportation application. The ability to cold start is governed by whether the fuel cell is able to overcome 0 °C before the produced ice terminates the electrochemical reaction. Therefore, fundamental understanding of the fuel cell performance at sub-freezing temperatures is highly needed to improve its cold start characteristics. In this work, we investigated the fuel cell sub-freezing operation through experimental investigation. PEFCs using various membranes and catalyst layer configurations were constructed. In particular, various catalyst layer thickness, ionomer-catalyst ratios, RHs, and membrane thicknesses were considered, and their influence on fuel cell cold start performance was investigated. The voltage, current, high-frequency resistance, and the coulombs passed before failure were recorded and presented to reveal the fuel cell cold start operation. Further, a simplified analysis of cold start was performed based on an electrode model. The cell voltage evolution and solid water build up were predicted and compared with the experimental data.

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