Low-loaded catalyst layers for proton exchange membrane fuel cell dynamic operation part 1: Experimental study

•Low Pt-loading catalyst layers (CL) of PEMFC were prepared and tested.•Hysteresis in polarization plots is due to water/thermal management and Pt-oxides.•Increased Pt-loading induces heterogeneous transport across CL thickness.•Saturation in CL pores changes the accessibility of Pt to protons.•Potential-dependant Pt surface state is impacted by ionomer adsorption/desorption. In the past decades, the proton exchange membrane fuel cell (PEMFC) components, cell/stack designs and system architecture have been significantly improved. However, despite great initial performance, PEMFC systems still suffer technological limitations, such as their initial cost, partly due to the use of expensive Pt-based electrocatalyst, which prevents widespread industrial deployment. Lowering the cathode catalyst loading while keeping high (and durable) catalytic activity has been intensively studied. In this work, low-loaded catalyst layers (20 and 100 µgPt cmgeo−2) are tested in PEMFC differential single-cell (DC) under high reactant stoichiometry to characterize their intrinsic electrochemical properties under various ideal and well-controlled operating conditions of cell temperature (T) and relative humidity (RH). Particularly, the change of the membrane hydration state, via the ohmic resistance measurement, and the Pt-oxides surface coverage are investigated to gather information on the physico-chemical and electrochemical mechanisms involved in the cathode active layer, and the typical performance hysteresis observed during dynamic operation such as polarization curves. These specific electrochemical measurements further enable to build a dataset, that can be used to improve PEMFC models taking into account the complex ORR mechanism, and the role of the Pt oxides in catalyst layer transient operation and degradation.