Non–Pt Catalyst Layer Operation in a PEM Fuel Cell: A Variable‐thickness Regime

Abstract

A recently pubilshed experimental polarization curve of a PEM fuel cell with the non–Pt cathode catalyst layer (CCL) exhibits unusual feature: in the region of small current densities, the curve is close to linear. We report a model for the CCL performance which explains this effect. The model includes finite rate of the oxygen adsorption on the catalyst surface. Qualitatively, due to a very high exchange current density of the non–Pt catalyst, the ORR rate close to the membrane is determined by the potential–independent oxygen adsorption rate. This leads to a specific regime of the CCL operation, when only part of the CCL thickness contributes to current production, while the rest part is completely inactive. With the growth of the cell current, the active part increases in width, while the inactive part shrinks. The resulting polarization curve appears to be close to linear.

Loading Impact of a PGM-Free Catalyst on the Mass Activity in Proton Exchange Membrane Fuel Cells

“…For fuel-cell applications, constraints in the catalyst layer thickness need to be considered, since both mathematical models and experimental works in the literature show that the thickness of the catalyst layer plays an important role in terms of specific current and stability/durability, depending on the operating regime. 8,[17][18][19] PGM-free catalyst layers of ≈4 mg cat cm −2 MEA , mentioned earlier, thereby correspond to a thickness of ≈100 μm, which is approximately ten times thicker than in the case of conventional Pt/C electrodes. 10,20 Such thick electrodes somewhat negatively affect the stack dimensions (≈4 cm additional length for a 400-cell stack), but more importantly, transport resistances that are negligible for the ≈10 μm thick Pt-based catalyst layers are expected to play a more significant role for the ≈100 μm thick PGM-free catalyst layers.…”