Enhanced understanding of electrothermal dynamics kinetic behavior for commercial-size PEM fuel cells based on impedance and distributed temperature measurement

Proton exchange membrane (PEM) fuel cells convert enthalpy change energy into heat and electricity, making it crucial to understand their electrothermal dynamic response to improve performance. However, existing studies on the transient response of PEM fuel cells mainly focus on voltage output, largely overlooking thermal transients. This study addresses this gap by using an embedded temperature sensor to capture the temperature and temperature change rate distribution in a 300 cm² PEM fuel cell. To further elucidate the electrothermal response and internal mechanisms, we employ fixed-frequency impedance spectroscopy as a complementary technique. Through a relaxation time distribution approach, impedances at strategically chosen frequencies (1800 Hz, 316 Hz, and 25 Hz) are used to quantify trends associated with proton transfer loss, charge transfer loss, and mass transfer loss, respectively. Building on this foundation, we explore the influence of loading mode, loading rate, and temperature on the PEM fuel cell's dynamic response. Subsequently, a detailed explanation is provided on how electrochemical transients translate into thermal transients. Our findings reveal a non-uniform temperature distribution across the cell's active region, highlighting the interplay between thermal dynamics and output performance. As temperature increases, the temperature differential widens, impacting the equilibrium between energy transfer and heat generation. This research introduces a groundbreaking concept: utilizing the rate of change of steady-state temperature as an indicator of the local heat source/sink relationship within the cell. This innovation presents a valuable tool for future investigations.