Ultrahigh Proton Conductivities of Postmodified Hf(IV) Metal–Organic Frameworks and Related Chitosan-Based Composite Membranes
Xin Chen, Shuai‐Long Zhang, Shang-Hao Xiao, Zifeng Li, Gang Li
Abstract
Recently, researchers have focused on preparing and studying proton exchange membranes. Metal–organic frameworks (MOFs) are candidates for composite membrane fillers due to their high crystallinity and structural characteristics, and Hf-based MOFs have attracted our attention with their high porosity and high stability. Therefore, in this study, Hf-based MOFs were doped into a cost-effective chitosan matrix as fillers to fabricate composite films having excellent proton conductivity (σ). First, the nanoscale MOFs Hf-UiO-66-(OH) 2 ( 1 ) and Hf-UiO-66-NH 2 ( 2 ) were chemically modified by a ligand design strategy to obtain SA-1 and CBD-2 bearing free −COOH units. The proton conductivities of SA-1 and CBD-2 under optimal test conditions reached 1.23 × 10 –2 and 0.71 × 10 –2 S cm –1 . After that, we prepared composite membranes CS/SA-1 and CS/CBD-2 by the casting method; tests revealed that the introduction of MOFs improved the stabilities and σ values of the membranes, and their best σ could reach above 10 –2 S cm –1 under 100 °C/98% RH. Further structural characterization and activation energy calculation revealed the conductive mechanism of the composite films. This investigation not only proposes a novel chemical modification method for optimizing the σ of MOFs but also promotes the development of MOF-doped composite membranes and provides a basis for future applications of MOFs in fuel cells.