Sulfonated MOF‑Enhanced Nafion Membranes for High‑Temperature, Durable Proton Exchange Membrane Water Electrolysis

High-temperature proton exchange membrane water electrolysis (HT-PEMWE) is a promising strategy for low-energy, high-efficiency hydrogen production. However, practical implementation relies critically on the development of novel PEMs that simultaneously offer high proton conductivity and long-term stability at high temperatures. While metal-organic frameworks (MOFs) have been widely investigated as high-performance proton-conducting materials, their specific incorporation into Nafion matrices for HT-PEMWE remains largely unexplored. In this work, we designed and fabricated a sulfonated MOF-reinforced Nafion (S/N-Nafion) composite membrane. The S/N-Nafion membrane achieved a proton conductivity of 154.7 mS cm^-1 at 100 °C, which is twice that of recast Nafion (75.6 mS cm^-1), while also possessing excellent mechanical strength and dimensional stability at elevated temperatures. When used as the solid electrolyte, an electrolyzer with S/N-Nafion reached only 1.59 V at 120 °C and 3.0 A cm^-2, which is 120 mV lower than recast Nafion (1.71 V) under the identical conditions. Moreover, during a 300-h durability test at 120 °C and 1.0 A cm^-2, the S/N-Nafion-PEMWE exhibited an extremely low voltage decay rate of 6.0 µV h^-1. These results underscore the immense potential of the S/N-Nafion membrane for enabling highly efficient and stable high-temperature electrolytic hydrogen production.