Influence of Ionomer Overcoating on the Interfacial Properties and Performance of Gas Diffusion Electrode-Based Proton Exchange Membrane Fuel Cells

Membrane electrode assemblies (MEA) based on gas diffusion electrodes (GDEs) usually suffer from greater ohmic losses and proton transport resistances owing to poor contact at the membrane–catalyst layer (CL) interface. This affects the overall performance of the proton-exchange-membrane fuel cells (PEMFCs). To address this, it is essential to strengthen the interface between the membrane and CL, especially at the cathode side. In this context, the present work is focused on engineering the membrane–CL interface by applying an optimized Nafion ionomer overcoat on top of a Mayer-rod-coated cathode-GDE, within an asymmetric MEA architecture. The role of the Nafion overcoat in improving the membrane–CL interface is inferred from morphological observations and in situ electrochemical characterizations. The electrochemical evaluation indicates the critical role of the ionomer overcoat on GDE, followed by the hot pressing during MEA fabrication, in improving the PEMFC performance. Furthermore, the surface characteristics of the overcoated GDEs have been characterized by profilometry and scanning electron microscopy. The findings suggest progressive smoothening of the CL surface with increasing ionomer overcoat concentration till 10 wt.% and further increase leads to crack generation. The polarization behavior of the overcoated (0–20 wt.%) GDE-MEAs identifies 10 wt.% as the best-performing sample among the discrete cases examined, corresponding to an ~4.8 μm ionomer overlayer (0.86 mg cm−2). This configuration exhibits the lowest ohmic resistance and improved proton and mass transport behavior, suggesting enhanced interfacial interaction based on HFR/EIS trends. In addition, the study of relative humidity (RH) transitions (100% RH → 40% RH) and polarization curves indicate superior performance of the 10 wt.%-overcoated GDE-MEA compared to the catalyst-coated membrane (CCM) type MEA under fully humidified conditions. This study manifests that interfacial engineering is highly effective in fabricating a high-performance GDE-based MEA for PEMFCs.