Achieving excellent proton conductivity and power density by introducing stable nitrogen-rich carbonized metal-organic frameworks into high-temperature proton exchange membranes

Abstract

The introduction of metal-organic frameworks (MOFs) into polybenzimidazole (PBI) as high temperature proton exchange membranes has attracted extensive attention. In this work, nitrogen-rich carbonized MOFs derived from UIO-66-NH2 were synthesized, exhibiting superior chemical stability under concentrated phosphoric acid (PA) and high-temperature conditions compared to conventional MOFs. The composite membranes were prepared by introducing these nitrogen-rich carbonized MOFs into PBI for the first time. Remarkably, the carbonized MOFs demonstrated a triple synergistic proton-conduction mechanism: retained porous architecture as proton-conducting channels; nitrogen-rich sites enabling proton hopping through acid-base pairs; and self-driven proton conduction via in situ-generated zirconium phosphate. Notably, even at lower levels of PA doping, the proton conductivity reached 0.079 S cm-1, surpassing that of both porous carbon-based and zirconia-based composite membranes. Furthermore, the interaction between PBI and the carbonized MOFs substantially enhanced the mechanical properties of the composite membrane, with the elongation at break increasing more than 8 times relative to these composites. These conductivity and mechanical enhancements contributed to achieving a peak power density of 952 mW cm-2, which, to the best of our knowledge, represents the highest reported value for PA doped inorganic/polymer-based high-temperature proton exchange membrane fuel cells (HT-PEMFCs). This work highlights the potential of nitrogen-rich carbonized MOF-based composite membranes for high-power-density and long-term stable HT-PEM applications.