Perfluorosulfonic acid membranes with reduced hydrogen permeation by filling with carbon quantum dots for fuel cells

Carbon quantum dots (CQDs) are compatible with perfluorosulfonic acid (PFSA) polymers due to their rich hydrophilic functional groups and nanoscale particle size, making them suitable as inorganic fillers for proton exchange membranes. In this work, CQDs synthesized by a simple microwave-assisted pyrolysis method were used to improve the performance of PFSA proton exchange membranes. Research indicates that at 80 °C and 100% relative humidity (RH), the proton conductivity of the PFSA membrane increased to 254 mS/cm with the addition of 0.5 wt% CQDs filler, compared to 249 mS/cm for the original PFSA membrane. This enhancement in proton conductivity is likely attributed to the hydrophilic functional groups present on CQDs, such as carboxyl groups (–COOH) and amino groups (–NH 2 ). Furthermore, a notable decrease in hydrogen permeability was observed in the composite membranes due to the incorporation of CQDs. Specifically, the hydrogen permeability of the PFSA/CQDs-2 composite membrane was reduced by approximately 44% compared to the original PFSA membrane. This reduction in hydrogen permeability is likely a result of cross-linking between the sulfonic acid groups in PFSA and the amino groups in CQDs. In conclusion, CQDs contribute to better proton conductivity, lower hydrogen permeability, and enhanced thermal and mechanical stability for PFSA membranes, making them a potential membrane material for high-temperature operation in proton exchange membrane fuel cells.