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

Abstract

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 °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 °C (0% RH). The composite membrane fuel-cell stably withstand a constant current discharge of 200 mA cm −2 for 200 h (160 °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. • Metal–organic frameworks (MOF) grafted with phosphoric acid ligand is synthesized. • The unique MOF greatly enhances performance of phosphoric acid doped PBI membrane. • 1:2G–UIO-66@OPBI HT-PEM achieves the highest proton conductivity (0.124 S cm −1 . • The HR-PEM fuel cell exhibits an excellent long-term stability. • The HR-PEM fuel cell achieves a peak power density 725 mW cm −2 at 160 °C (0% RH).