Constructing proton transport channels in low phosphoric-acid doped polybenzimidazole membrane by introducing metal-organic frameworks containing phosphoric-acid groups

Proton-exchange membranes (PEMs) are considered as core components of high-temperature fuel cells. Phosphoric acid (PA) plays a pivotal role in the performance of PEMs and is especially vital for conductivity. This work reports the firstly successful preparation of metal-organic frameworks grafted with phosphate functionalized ligand, which introduce efficient, high-performance proton transport channels. At a ligand replacement ratio of 1:2, the conductivity of 40% hydroxyphosphono-acetic acid-type UIO-66@OPBI membrane is 0.097 S cm(-1) at 160 degrees C (0% RH), and the power density of the fuel cell achieves 640 mW cm(-2). When the UIO-66 ligand is replaced with glyphosine containing two phosphate groups at the same ratio (1:2, 40% composition), the highest conductivity of the composite membrane is 0.124 S cm(-1), and the power density of the fuel cell reaches 725 mW cm(-2) at 160 degrees C (0% RH). The composite membrane fuel-cell stably withstand a constant current discharge of 200 mA cm(-2) for 200 h (160 degrees C, 0% RH) with a voltage attenuation rate of only 0.042 mV h(-1) from 60 to 200 h, lower than that of the 1:2H-UIO-66@OPBI membrane (0.066 mV h(-1)) under the same conditions.

Automated summary

This study successfully prepared metal-organic frameworks grafted with phosphate functionalized ligands, introducing efficient proton transport channels for high-temperature fuel cells. The composite membrane fuel cell showed improved conductivity and power density at 160 degrees C under 0% relative humidity. Additionally, the stability of the cell under constant current discharge was demonstrated, with a low voltage attenuation rate over 200 hours.