Catalyst layers for fluorine‐free hydrocarbon PEMFCs

Abstract

Herein, we study catalyst ink composition on the current-voltage characteristics of fuel cells incorporating fully hydrocarbon-based membrane-electrode-assemblies. The membrane and ionomer used for these studies is sulfo-phenylated poly(phenylene) biphenyl (sPPB-H+). Fuel cell current-voltage characteristics vary depending on the nature of the dispersing medium of the ink with single-cell power densities increasing for inks prepared from MeOH > EtOH > iPrOH, based on 3:1 alcohol:water mixtures. This correlates with the catalyst layer's higher BET- surface area, porosity, electrochemically active surface area (ECSA), and lower cathodic charge transfer resistance. Despite this, MeOH-based catalyst inks yield catalyst layers with relatively high ionic resistance, which is postulated to result from the poor integrity of ionomer films coating C/Pt aggregates within the catalyst layer. This deficiency is mitigated using low surface area Vulcan XC-72 catalyst support. Using low surface area carbon supports, a satisfactory proton conduction network can be established in the catalyst layer with ionomer contents as low as 2.5 wt% (∼0.023 mgionomer cm-2), with a > 10% increase in peak power density (H2/Air) compared to a conventional D520-Nafion®-based MEA containing 30 wt% ionomer in the catalyst layer (∼ 0.28 mg cm-2).