Triple-Phase Boundary Regulation via In Situ Quaternization of the Polybenzimidazole Ionomer for High-Temperature Proton Exchange Membrane Fuel Cells

Abstract

Polytetrafluoroethylene (PTFE) is the most widely used catalyst layer (CL) binder in a polybenzimidazole phosphoric acid (PBI–PA)-based high-temperature proton exchange membrane fuel cell (HT-PEMFC) due to its great hydrophobicity. However, PTFE also limits the formation of an effective triple-phase boundary (TPB) due to its strong resistance to acid retention. To obtain the composite ionomer in the CL of HT-PEMFC, polybenzimidazole (PBI) is thus invited. Then, an in situ quaternization strategy on PBI is developed to increase the TPB concentration in CL by controlling the PA distribution and taking into account the superior PA retention capability of quaternary ammonium groups. At the same time, Pt active sites can be freed and mass transfer channels can be in situ constructed. Consequently, the corresponding HT-PEMFC fed with H₂/O₂ attains a maximum power density of 755 mW/cm² and an electrochemical surface area of 35.56 cm²/mg_Pt, surpassing those equipped with PTFE by 10 and 30%, respectively. The electrochemical performance improvement indicates that the in-situ quaternization strategy on the ionomer has great application potential in practical HT-PEMFC manufacturing.