Enhanced proton conductivity in a Cu-BTC thin-film membrane through lysine incorporation and a mixed matrix membrane

Abstract

To meet the growing demand for clean and sustainable energy, the development of high-performance proton conductive materials is crucial for practical applications in PEMFCs. However, the current materials suffer from issues such as low conductivity, poor durability, and unclear structure–activity relationship. To address these challenges, we investigate the proton conductivity properties of lysine-decorated Cu-BTC (where BTC is benzene-1,3,5-tricarboxylate) and its corresponding thin-film membrane. We explore the impact of lysine (Lys) content (10 wt%, 20 wt%, 30 wt%, and 40 wt%) on the proton conductivity performance under varying humidity and temperature conditions. Our findings show that Cu-BTC-Lys (40 wt%) exhibits the best conductivity of 1.2 × 10⁻³ S cm⁻¹ at 80 °C under 100% relative humidity (RH), aided by an activation energy (E_a) of 0.25 eV facilitating proton transfer through hydrogen-bonding networks via the Grotthuss mechanism. We then create a proton conductive membrane by fabricating Cu-BTC-Lys (40 wt%) with the PVP/PVDF polymeric matrix. The resulting Cu-BTC-Lys@PVP/PVDF-20 membrane shows a significantly improved conductivity of 4.8 × 10⁻³ S cm⁻¹ at 80 °C under 100% RH, along with a decreasing E_a value of 0.15 eV. The membrane retains its rich hydrogen-bonding networks and excellent performance durability for up to 5 days, making it an ideal candidate for real-life applications.