Fluorinated polybenzimidazole as binders for high-temperature proton exchange membrane fuel cells

Abstract

The performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs) is highly affected by the binders in the catalyst layer. However, the currently commonly used binders such as acidophilic polybenzimidazoles (PBIs) and hydrophobic fluorinated polymers (e.g. PTFE) could not conduct protons or facilitate rapid gas transport simultaneously. Herein, two fluorinated PBIs (F6PBI and F4PBI) are designed and synthesized as binder materials from the easily obtained monomers of hexafluoroglutaric acid (HFGA) and tetrafluoroterephthalic acid (TFPA). Combined with the good proton conductivity of PBI and high fuel permeability of PTFE, the H2/O2 single cell based on PA/mPBI membrane using F6PBI binder in catalyst layer exhibits a larger electrochemical surface area (ECSA) of 67 cm2/mgPt corresponding to a Pt-mass specific power density of 1.41 W/mgPt. Therefore, the MEA achieved the highest peak power density of 705 mW/cm2 at 160 °C with F6PBI binder of 5 wt% and catalyst of 0.50 mgPt/cm2, which is over 100 mW/cm2 higher than MEAs using mPBI and PTFE as binder materials. And the H2/O2 cell using F6PBI binder exhibits good stability of more than 800 h at a current of 0.3 A/cm2 at 160 °C.