Experimental study on the application of stack voltage distribution fluctuations in operational monitoring and fault diagnosis: Analyzing the effects of stack degradation on monitoring accuracy and validating it in an 80 kW fuel cell stack

To address the “black box” issue in commercial proton exchange membrane fuel cell (PEMFC) stack operation, this study proposes a Voltage Trend Rate (VTR) algorithm. Using an 80 kW PEMFC stack as the test subject, a 2000-h accelerated degradation test was conducted under VTR monitoring to explore stack degradation mechanisms and validate the VTR's full-lifecycle performance. Results show: stack performance degradation mainly stems from increased activation voltage loss (86.09% of total voltage loss increase); catalyst layer exhibits significant thickness decay (32.49% for cathode, 42.15% for anode), due mainly to Pt particle agglomeration (anode/cathode average size: 2.57/2.66 nm → 6.25/6.46 nm) and loss, with minimal carbon support corrosion; in the membrane electrode assembly, elemental loss rate is F > Pt > C. though Pt has the second-highest loss rate, much Pt migrates into the proton exchange membrane (PEM) to form deactivated Pt bands; F mass fraction drops from 43.43% to 19.3%, yet Pt bands compensate, limiting PEM thickness decay to only 5.99%. Moreover, degradation alters optimal stack operation: optimal cathode stoichiometry rises from 1.8 to 2.0, and optimal temperature from 70 °C to 75 °C, with parameter adjustments mitigating adverse effects from reduced Pt activity and increased gas diffusion layer hydrophilicity. Finally, VTR evaluation confirms its stability: 1-s moving window mean filtering captures minor operating condition changes, and its judgment threshold only rises from 10.4% to 11.0% over 2000 h, requiring no frequent revisions. This study supports efficient, stable PEMFC stack operation and commercial application.