Impact of shutdown operations on the recovery of reversible degradation in proton exchange membrane fuel cells

Abstract

In proton exchange membrane fuel cells, partial performance loss accumulated during long-term operation can be recovered through optimized operation or shutdown, a process known as reversible degradation. However, most existing studies focus on small-scale single cells and laboratory-scale test conditions, without adequately considering the constraints inherent to practical system-level operation. Therefore, investigating the influence of practically adjustable shutdown parameters on recovery effectiveness is crucial. Moreover, large-scale stacks exhibit spatial heterogeneity in degradation and recovery, both across cell positions and within individual cells. This heterogeneity plays a key role in identifying reversible degradation and formulating recovery strategies. In this study, accelerated stress tests were conducted on a full-size short stack under New European Driving Cycle conditions. Experimental variables included shutdown temperature, operating temperature, and purging methods, to evaluate their effects on recovery. Changes in stack consistency and electrochemically active surface area before and after recovery were analyzed. Results indicate that moderate retention of condensed water promotes ionomer rehydration and performance recovery, while uneven water distribution leads to spatial differences in recovery. Inter-cell and in-plane inconsistencies increase with current density, with voltage deviations exceeding 40 mV between cells and 20 mV within cells at 594 A. The outlet region exhibited weaker recovery consistency and greater sensitivity to load fluctuations, with response amplification reaching approximately 300 %. Cooling measures during recovery improved both steady-state performance and dynamic response. This work provides important insights into the optimization of shutdown parameters and spatial performance variation in large PEMFC stacks, supporting the development of improved operational strategies to enhance durability and efficiency in practical applications.