Electrochemical signatures in proton exchange membrane fuel cells: A comprehensive study based on distribution of relaxation times

The impedance response of a proton exchange membrane fuel cell (PEMFC) was analyzed using the Distribution of Relaxation Times (DRT) under varied operating conditions of load, temperature, pressure, stoichiometry, and oxidant type. Six relaxation processes were identified and characterized through their resistance and time constant evolution. A non-linear regression framework quantified their statistical significance and correlations with operating parameters, while reconstruction errors and confidence intervals revealed non-negligible uncertainties affecting interpretation. The highest-frequency contribution appears mainly as a DRT regression artifact, though its resistance still exhibits temperature dependence, possibly linked to proton transport or residual ohmic effects. Among the remaining high-frequency features, one is statistically insignificant, while another shows mixed dependencies, suggesting the superposition of multiple concurrent processes. Mid- and low-frequency contributions vary coherently with temperature, pressure, and load, consistent with charge-transfer and mass-transport phenomena. Overall, the work establishes a quantitative link between operating parameters and internal processes, advancing the diagnostic and predictive capabilities of DRT for PEMFCs.