Efficient Separation of Helium Isotopes via Resonant Tunneling in Bilayer FePc Membranes

Quantum sieving in two-dimensional membranes offers a promising route for helium isotope separation, and several monolayer materials have been predicted to approach industrial benchmarks criteria. In this work, two-dimensional polymerized iron phthalocyanine (FePc) membranes are employed as a platform to investigate how interlayer stacking can enhance 3He/4He separation. Using first-principles calculations, we construct penetration energy profiles for 3He and 4He along the minimum-energy permeation pathway and explicitly incorporate isotope-dependent zero-point energy corrections to obtain effective one-dimensional barriers. Quantum transport analysis based on these barriers shows that a monolayer FePc membrane yields 3He/4He selectivity below industrial benchmarks criteria, while stacking two FePc layers generates a well-defined double-barrier landscape with an interlayer potential well that supports resonant tunneling in the confined region. Within an interlayer spacing window of 3.25–3.45 Å, the bilayer FePc membrane simultaneously achieves industrial benchmarks criteria for permeance and selectivity at cryogenic temperatures. Especially, at an interlayer spacing of 3.35 Å, it delivers a 3He/4He selectivity of 1612.1 and a 3He permeance of 4.29 × 10–7 mol s–1 cm–2 bar–1 at 8 K. These results elucidate how interlayer resonant tunneling can be harnessed to amplify isotope-dependent quantum effects and provide rational design guidelines for high-performance multilayer quantum-sieving membrane for helium isotope separation.