Kinetic Control of Angstrom-Scale Porosity in 2D Lattices for Direct Scalable Synthesis of Atomically Thin Proton Exchange Membranes

Angstrom-scale pores introduced into atomically thin 2D materials offer transformative advances for proton exchange membranes in several energy applications. Here, we show that facile kinetic control of scalable chemical vapor deposition (CVD) can allow for direct formation of angstrom-scale proton-selective pores in monolayer graphene with significant hindrance to even small, hydrated ions (K+ diameter similar to 6.6 angstrom) and gas molecules (H2 kinetic diameter similar to 2.9 angstrom). We demonstrate centimeter-scale Nafion| Graphene|Nafion membranes with proton conductance similar to 3.3-3.8 S cm-2 (graphene similar to 12.7-24.6 S cm-2) and H+/K+ selectivity similar to 6.2- 44.2 with liquid electrolytes. The same membranes show proton conductance similar to 4.6-4.8 S cm-2 (graphene similar to 39.9-57.5 S cm-2) and extremely low H2 crossover similar to 1.7 x 10-1 - 2.2 x 10-1 mA cm-2 (similar to 0.4 V, similar to 25 degrees C) with H2 gas feed. We rationalize our findings via a resistance-based transport model and introduce a stacking approach that leverages combinatorial effects of interdefect distance and interlayer transport to allow for Nafion|Graphene|Graphene|Nafion membranes with H+/K+ selectivity similar to 86.1 (at 1 M) and record low H2 crossover current density similar to 2.5 x 10-2 mA cm-2, up to similar to 90% lower than state-of-the-art ionomer Nafion membranes similar to 2.7 x 10-1 mA cm-2 under identical conditions, while still maintaining proton conductance similar to 4.2 S cm-2 (graphene stack similar to 20.8 S cm-2) comparable to that for Nafion of similar to 5.2 S cm-2. Our experimental insights enable functional atomically thin high flux proton exchange membranes with minimal crossover.

Automated summary

Introducing angstrom-scale pores into atomically thin 2D materials through chemical vapor deposition enables high flux, proton-selective proton exchange membranes, with in-depth analysis conducted through impedance transport models and stacking methods.