Influence of catalyst layer polybenzimidazole molecular weight on the polybenzimidazole-based proton exchange membrane fuel cell performance

The catalyst layer (CL) of a polybenzimidazole (PBI) membrane electrode assembly (MEA) consists of Pt–C (Pt on a carbon support), PBI, and H3PO4. Two series of catalyst ink solutions each containing Pt–C, N,N′-dimethyl acetamide, and PBIs comprising four different molecular weights (MWs) (i.e., Mw = 1.1 × 104, 4.4 × 104, 9.0 × 104, and 17.4 × 104 g mol−1) are used to fabricate CLs. One catalyst ink solution series is mixed with LiCl, while the other solution series lacks LiCl. We demonstrate that the CL prepared using a lower MW PBI has a higher electrochemical surface area, lower charge transfer resistance, and higher fuel cell performance. The addition of LiCl enhances the dispersion of the high MW PBIs in the catalyst ink solution and acts as a foaming agent in CL, thus improving fuel cell performance. However, LiCl exerts small influence on the fuel cell performance of the MEAs fabricated using low MW PBIs.