Enhancement of Proton Conductivity in Water and Aqua-Ammonia Vapor by Incorporating Sulfonic Acid-Functionalized Polymer into MIL-101-SO₃H

The design and preparation of super proton conducting metal-organic frameworks (MOFs) are of great significance for the advancement of proton exchange membrane fuel cells (PEMFCs). An effective approach to increase the sulfonic acid density and control the hydrogen bonding networks within MOFs involves incorporating polymer chains that contain sulfonic acid groups into their pore structures. In this work, we report the <i>in situ</i> synthesis of a polyvinyl sulfonic acid (PVS) cross-linked polymer within the nanopores of MIL-101-SO₃H, resulting in the PVS@MIL-101-SO₃H composite. This composite maintains high proton conductivity in pure water vapor, achieving a peak conductivity of 2.57 × 10^-2 S·cm^-1 at 85 °C and 98% relative humidity (RH). Significantly, the proton conductivity markedly increases in aqua-ammonia environments, reaching 1.21 × 10^-1 S·cm^-1 under 1.0 M aqua-ammonia vapor at 100 °C, approximately five times higher than that observed in pure water vapor. Moreover, the composite exhibits excellent stability. Therefore, this study offers an efficacious approach to enhancing the performance of aqua-ammonia-assisted solid-state proton-conducting materials.