Hydration state measurement in polymer electrolyte fuel cells from correlated neutron imaging and single-point impedance

Journal article

Effective water management remains a critical challenge for polymer electrolyte fuel cell (PEFC) durability and reliability, necessitating accurate real-time hydration state monitoring. Full-spectrum electrochemical impedance spectroscopy (EIS) struggles to balance diagnostic speed with accuracy, and the linkage between microscopic liquid water distribution and macroscopic EIS parameters remains inadequately resolved. This study introduces a novel method using the 40 Hz single-frequency impedance phase angle, integrated with operando neutron imaging, for non-invasive, rapid hydration state assessment in operating PEFCs. The methodology was validated across three operational modes (Drying, Normal, Flooding). While conventional parameters like high-frequency resistance (HFR) effectively identified membrane dehydration and low-frequency resistance (LFR) detected cathodic flooding, neutron imaging revealed that neither HFR nor LFR consistently correlated with total liquid water mass across all states. Specifically, LFR showed strong water mass correlation in Drying mode (r = 0.98) but declined significantly in Normal (r = 0.76) and Flooding (r = 0.39) modes. In contrast, the 40 Hz phase angle maintained strong positive correlations (r ≥ 0.89) universally across all hydration states and operational regimes. Crucially, terminal voltage remained stable despite substantial hydration fluctuations during Normal mode operation (e.g., water mass: 98–111 mg; phase angle: 25.1°–27.5°), underscoring its inadequacy for hydration detection. The phase angle also dynamically captured pore-blocking and channel-clearing events during Flooding mode, while voltage responses lagged behind mass transport limitations. These findings establish the 40 Hz impedance phase angle as a rapid, accurate, and robust indicator for real-time PEFC hydration assessment, enabling future advanced water management strategies.

Authors: Wu, Y; Zhou, S; Chen, J; Li, B; Li, J

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Energy
• Volume: 344
• Article number: 139764
• Publication date: 2025-12-22
• Acceptance date: 2025-12-21
• DOI: 10.1016/j.energy.2025.139764
• EISSN: 1873-6785
• ISSN: 0360-5442
• Language: English
• Keywords: polymer electrolyte fuel cells; water management; electrochemical impedance spectroscopy; neutron imaging; phase angle