Electrochemical assessment of contact pressure effects on durability of high-temperature proton exchange membrane fuel cells under dynamic operation

Abstract

This study examines the impact of nominal contact pressure on the electrochemical performance and degradation behaviour of high-temperature proton exchange membrane fuel cells (HT-PEMFCs) with pre-doped polybenzimidazole (p-PBI) membranes, focusing primarily on start-stop cycling durability. Three nominal contact pressures—0.30 MPa, 0.55 MPa, and 0.85 MPa—were applied during 70-cycle start-stop tests. Performance evolution was assessed using polarization curves, electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT), and spatial current density mapping. Complementary steady-state tests were conducted on separately activated MEAs to evaluate the role of both activation and operational nominal contact pressures. MEAs activated at 0.55 MPa achieved 2.5 % higher voltage at 0.4 A/cm² compared to those activated at 0.30 MPa. Independently, increasing the operational contact pressure from 0.30 MPa to 1.00 MPa resulted in a 2.2 % voltage improvement, confirming the dual influence of activation and mechanical compression on fuel cell performance. Under dynamic conditions, 0.85 MPa offered the highest initial voltage but suffered the most severe degradation (21.3 % voltage loss), while 0.30 MPa preserved durability with reduced initial performance. The intermediate 0.55 MPa pressure provided the optimal balance, with the highest Unified Performance Index (UPI = 1.94). Post-mortem thickness analysis and Pearson correlation ( r = –0.97 to –0.98, p < 0.001) confirmed strong spatial links between mechanical thinning and electrochemical degradation. These results demonstrate that optimized activation and operating nominal contact pressure are essential for enhancing long-term performance and mechanical stability in HT-PEMFC systems under cyclic conditions.

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