Operando investigations of proton exchange membrane fuel cells performance during air interruptions in dry and humidified conditions

Abstract

Activating proton exchange membrane fuel cells is crucial to systematically build proton conductive pathways, remove contaminants from the electrode surface and obtain the highest performances, with air interruption emerging as one of the most powerful methods. While this approach enables fast activation and considerable recovery after extended periods of shutdown or operation, the impact of relative humidity on this process has not been explored. Herein, the impact of the relative humidity on the air interruption is investigated using an array of operando methods such as polarization, electrochemical impedance spectroscopy, and high-resolution localized current and mapping. It is found that while air interruptions in humidified conditions can improve performance, they rapidly reduce them in dry conditions. Specifically, air interruptions in fully humidified conditions improve ions, charges, and gas diffusion to the active sites, which may be attributed to the removal of platinum oxides increasing active site availability. However, air interruptions under low relative humidity rapidly reduce the cell voltage by increasing charge transfer and mass transport limitations, while causing extensive overheating as the cell is starved of oxygen and hydrogen might be generated. Overall, this work reveals the potential, yet limitations of air interruptions in operando hydrogen fuel cells.