A dual-constrained assembly strategy of highly aligned two-dimensional montmorillonite membranes for efficient proton transport†

Driven by the boosted demand for energy storage and conversion devices, highly conductive proton exchange membranes (PEMs) are extremely desired. Assembling atomically thin nanosheets into nanofluidic channels represents one promising way to construct high-performance PEMs. However, how to produce ultra-aligned nanofluidic channels in a universal and scalable manner is still challenging. Here, we report a dual-constrained assembly strategy to fabricate two-dimensional (2D) montmorillonite (MMT) membranes with highly ordered nanochannels and fast proton transport through confined modification with sulfonated polyvinyl alcohol (SPVA). The numerous polar functional groups with rich lone pair electrons of SPVA enabled nanosheets to feature more negative charges and additional proton carriers, improving the spatial orientation degree of nanosheet dispersion via the electrostatic confinement effect. The hydrogen bond interaction between SPVA and nanosheets offered a unique capillary force compensation effect to constrain nanochannel disordering during water removal. Consequently, the SPVA-modified MMT membrane presented significantly enhanced alignment of nanochannels, endowing it with ultra-high proton conductivity (134.58 mS cm⁻¹), ultra-low activation energy (9.19 kJ mol⁻¹), and excellent stability. This work provides a facile and general strategy for constructing high-performance PEMs, and opens an avenue for the development and design of highly aligned lamellar membranes.