• Transport impedance with Current-modulated Hydrogen flow-rate Spectroscopy (CH2S). • Effective diffusivities and mass transport resistances of hydrogen measured with CH2S. • GDL substrate and MPL layers operando transport properties differentiated. • Transport properties compared for passive-PEMFC and conventional-PEMFC • Current density and active area effects on hydrogen transport in passive PEMFC. Current-modulated Hydrogen flow-rate Spectroscopy (CH2S) is the mass-transport impedance that relates cell current ( I ˜ ) and hydrogen flow rate ( Q ˜ H 2 ) in the anode of a proton exchange membrane fuel cell (PEMFC). The transfer function ( H = n F Q ˜ H 2 / I ˜ ) provides kinetic information about transport processes in the anode of a PEMFC under working conditions. CH2S can differentiate hydrogen transport in the gas diffusion layer substrate (GDLS) and in the microporous layer (MPL) of the anode. Using an analytical model and the distribution of relaxation times formalism, the effective, operando , hydrogen diffusivities and mass transport resistances of the GDLS and MPL are obtained. Here CH2S is used to study mass transport in a PEMFC anode fed with quasi-static hydrogen and air atmospheres, or passive PEMFC (p-PEMFC). The anode is a commercial gas diffusion electrode, with Pt/C based catalyst layer, a hydrophobic carbon black MPL, and a woven carbon cloth GDLS. The results show larger mass transport losses in the GDLS of the p-PEMFC compared with a convective PEMFC (c-PEMFC) fed with gases under forced convection. The MPL, however, presents same mass transport losses in both cell types, with operando water saturation close to 100%. Increasing current density, up to 180 mA cm -2 , has little impact on GDLS transport properties but improves them in the MPL attributed to thermal activation and drier conditions in the anode by water electroosmotic dragging. Larger active area size increases transport losses in p-PEMFC due to more difficult passive elimination of water from the cell by natural forces. Changes in the p-PEMFC design are proposed to mitigate mass transport losses and bring its efficiency closer to the c-PEMFC.
Duque et al. (Sun,) studied this question.