Dibromoxylene-crosslinked sulfonated para-PBI membranes for use in high temperature polymer electrolyte membrane fuel cells operating with reformate gas

Abstract

According to literature, the reduced hydrophilicity of phosphoric acid (PA) doped PBI membranes in comparison to PA itself is advantageous in high temperature polymer electrolyte fuel cells (HT PEMFCs) fed with dry gases, because the presence of H₃O⁺ results in electro-osmotic drag and thus drying of the anode side. For HT PEMFC operated with water containing reformate, this should be less of an issue, and membranes with increased water contents are expected to have higher conductivity without being affected by anode drying. Therefore, this work investigates the properties and performance of a sulfonated para-PBI membrane, crosslinked with 5 wt% dibromoxylene (5MS-PBI), for use in reformate-fueled HT PEMFC. We show that the concentration of the absorbed acid is 82 wt% for 5MS-PBI but 90 wt% for commercial standard meta-PBI. Even though 5MS-PBI absorbs only half of the PA than meta-PBI, it shows an improved conductivity, and in the HT PEMFC operating with reformate (6.9% H₂O, 1.4% CO, 22.3 % CO₂, 69.3 % H₂), the power densities at 700 mA cm⁻² and 170°C, 1 bar backpressure were 434 with meta-PBI and 454 mW cm⁻² with 5MS-PBI. At 160°C, without backpressure, power densities were 364 and 401 mW cm⁻², respectively.