| Summary: | Polymer electrolyte membrane fuel cells have shown great promise as a clean and renewable energy source due to their high efficiency and lack of carbon emissions at point of use. However, one of the great challenges in their wider commercialisation is the lack of in-situ metrological techniques to measure performance of the devices over the course of their lifetime. In this work, novel transfer function analysis techniques are developed and applied to these devices to better understand their in-situ performance through perturbation and measurement of electrical, thermal, and pneumatic properties. Localised electrochemical impedance spectroscopy measurements using a novel reference electrode array are made to measure spatially resolved, cathode-specific fuel cell performance for the first time as well as membrane hydration transients when the fuel cell is polarised from open circuit. Electro-thermal impedance spectroscopy, a transfer function technique relating an electrical perturbation to a thermal response, is developed to characterise the electrically-dependent thermal performance of an open-cathode fuel cell and identify faults such as pinhole formation and bowing of lands. Electrochemical pressure impedance spectrscopy, a transfer function technique relating a cathodic pressure perturbation to an electrical response, is developed and applied to a fuel cell in order to characterise water management of a fuel cell under varying humidity conditions. The impact of the techniques developed is discussed with scope for further advancement deliberated. The relevance of the application of the techniques is highlighted to give novel and complementary information not easily accessible by more conventional metrological methodologies.
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