Ether-Group-Mediated Aqueous Proton Selective Transfer across Graphene-Embedded 18-Crown-6 Ether Pores

Nanoporous two-dimensional (2D) materials provide a new avenue for the design of zero-crossover proton selective membrane, which is critical for the development of direct methanol fuel cells and many other renewable energy systems. In this work, we investigate the aqueous proton selective conduction behavior across graphene-embedded 18-crown-6 ether pores using extensive ReaxFF molecular dynamics simulations. It is found that though there exists a vacuum gap between the aqueous phase and graphene membrane, the proton conduction behavior can be mediated by the crown ether functional groups and results in a low proton penetration energy barrier of 5.53 ± 0.29 kcal mol⁻¹, corresponding to a high proton conductivity of about 3.23 × 10⁵ S cm⁻². Meanwhile, the vacuum gap together with the small pore size can effectively block the transportation of other molecules such as methanol, resulting in a high proton−methanol selectivity of about 9.3 × 10²⁵. Our results indicate that functional groups can significantly influence the proton conduction behavior across nanoporous 2D materials, and graphene membrane with embedded 18-crown-6 ether pores is a promising candidate for zero-crossover proton exchange membrane.