A superprotonic membrane derived from proton-conducting metal-organic frameworks and cellulose nanocrystals

Metal-organic frameworks (MOFs) have emerged as proton conductors. However, their applications have been limited by their inability to form a self-standing membrane and their significant performance loss when incorporated into composite membranes. Herein, we report a simple strategy for fabricating a structurally and chemically stable proton-conducting MOF/cellulose nanocrystal (PCMOF/CNC) membrane. This PCMOF/CNC composite membrane has an extremely high MOF loading (89%) and low CNC content. With water-stable PCMOF10, this loading enables the retention of MOF properties, and the composite exhibits a proton conductivity of 1.44 x 10(-2) S cm(-1) at 85 degrees C and 95% relative humidity. The derived composite maintains its free-standing form, superprotonic conductivity during month-long heating/cooling cycles (indicating high mechanical strength), and excellent thermal and water resistance. We attribute the unprecedented proton conductivity and mechanical integrity of the membrane to the abundant hydrogen bonds between PCMOF10 and CNCs, confirmed through Fourier transform infrared spectroscopy and theoretical computations.