Study on a quantitative characterization method for reversible degradation during fuel cell operation

Under dynamic operation, proton exchange membrane fuel cells (PEMFCs) exhibit reversible degradation that is often recovered during routine shutdown and rest, which can mask underlying irreversible durability trends. If this shutdown–rest recovery is not explicitly quantified and separated, durability assessment and prognostic health indicators may be biased. This work develops a measurement-driven protocol to isolate reversible degradation (Urev) under an automotive-relevant, J1015-derived cycling load. A single PEMFC is operated with controlled cycling durations (1–4 h) and subsequent shutdown rest windows (3–48 h), with polarization curves and electrochemical diagnostics (EIS, CV, and LSV) collected before and after rest. Results show Urev increases with cycling duration and saturates at 3 h, while recovery with rest follows a finite relaxation behavior with marginal gains beyond 24–48 h. Indicator correlations are regime-dependent: at low current densities, Urev is mainly associated with changes in ohmic resistance (ΔRohm) and electrochemically active surface area (ΔECSA), whereas at high current densities it is primarily governed by changes in reciprocal insulation resistance (Δ(1/Rins)). These findings provide actionable triggers for in-service monitoring and mitigation of PEMFC degradation in practical operation.