Improved proton conductivity in UiO-66-(COOH)2@PP composites with reduced activation energy at low humidity

The proton exchange membrane (PEM) is vital in proton exchange membrane fuel cells (PEMFCs), but current PEMs face issues including low conductivity, poor durability, and instability in maintaining proton transport across varying temperatures. This study proposes an innovative approach to address this issue by incorporating UiO-66-(COOH)2 as a filler in a polymeric matrix comprising polyvinylpyrrolidone and polyvinylidene fluoride (abbreviated as PP). Significantly, this facilitates forming hydrogen bonds between UiO-66-(COOH)2 and the PP matrix. The UiO-66-(COOH)2@PP composite membranes are comprehensively characterized through PXRD, TGA-DSC, FTIR, and SEM analyses. The remarkable water adsorption performance observed in the UiO-66(COOH)2@PP-X series creates favourable conditions for enhancing proton conductivity. Proton conductivity studies highlight exceptional performance, particularly UiO-66-(COOH)2@PP-30 achieving a remarkable 5.8 x 10-3 S cm-1 at 98% RH, with sustained conductivity over one week. At 32% RH, UiO-66-(COOH)2@PP-30 exhibits a significantly reduced activation energy of 0.09 eV, indicating a stable proton transport pathway across a wide temperature range. Mechanism studies unveil that the collaborative interaction between UiO-66-(COOH)2 and PP establishes a continuous network of hydrogen bonds, strengthened by PP's hydrophilic properties. Additionally, the stabilization of water within UiO-66-(COOH)2 channels significantly contributes to the overall efficiency of proton conduction.