20.500.12556/RUL-182193 Mechanistic analysis of coupled humidification, backpressure, and cathode stoichiometry effects in HT-PEMFCs High-temperature proton exchange membrane fuel cells (HT-PEMFCs) based on phosphoric-acid-doped polybenzimidazole membranes are promising for reformate-fed systems, yet their performance is highly sensitive to system operating parameters. This study evaluates the influence of cathode stoichiometry (λ▫$_{air}$▫=1.8–2.5), reactant backpressure (0.0–2.0 barg at the anode and 0.0–1.8 barg at the cathode), and 5 % inlet humidification at 160 °C using polarization analysis combined with electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT), Kramers–Kronig validation, and Monte-Carlo uncertainty quantification. Relative to dry atmospheric operation (0.0 barg, 0 % RH), increasing backpressure reduces transport-related resistance by up to 43 % at λ▫$_{air}$▫=1.8 and 59 % at λ▫$_{air}$▫=2.5 (0.4 A/cm²). In contrast, introducing 5 % RH at atmospheric pressure increases mass transport resistance by approximately 36 % (λ▫$_{air}$▫=1.8) and 63 % (λ▫$_{air}$▫=2.5), while KK residuals increase by up to 48 % and 24 %, respectively. A Unified Operating Index (UOI) integrating voltage, resistance, and stability was developed to rank operating regimes. At 0.8 A/cm², λ▫$_{air}$▫=1.8 and 2.0–1.8 barg, humidification lowers the UOI by 75.8 % relative to dry operation (amplification factor ≈13.5). Increasing stoichiometry to λ▫$_{air}$▫=2.5 lowers this effect by ∼50 % under identical conditions but does not eliminate instability. Dry operation with higher stoichiometry and moderate backpressure provides the most suitable operating window. high-temperature PEM fuel cell distribution of relaxation times cathode stoichiometry reactants backpressure reactants relative humidity visokotemperaturne gorivne celice protonska izmenjevalna membrana porazdelitev relaksacijskih časov stehiometrija katode protitlak reaktantov relativna vlažnost reaktantov true false true Angleški jezik Slovenski jezik Članek v reviji 2026-04-29 12:34:04 2026-04-29 12:34:12 2026-04-30 04:31:13 0000-00-00 00:00:00 2026 0 0 20 str. Vol. 569, art. 148933 2026 0000-00-00 Zaloznikova Objavljeno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 621.352.6:539.125.4:662.611.2 0013-4686 10.1016/j.electacta.2026.148933 276710659 Todorovski_..._Mechanistic_analysis_....pdf Todorovski_..._Mechanistic_analysis_....pdf 1 289527CCFC50A350E7FC450DD58BB973 c50accaf644a6083d93dc231ac6d9181bd8dae4e9d5ea8317fbb743b36b0666d d9adede2-43b6-11f1-b0ab-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=233193 https://www.sciencedirect.com/science/article/pii/S001346862600825X 1 b37d5575-43b6-11f1-b0ab-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=233192 Fakulteta za strojništvo 0 0 0