Selectivity enhancement by the presence of HOF + CNT composite membranes investigated by non-equilibrium molecular dynamics

Hydrogen purification through membrane separation offers convenience and suitability for on-site operation, especially in automotive fuel cells that utilize reformed methanol as a hydrogen source. In this study, the molecular dynamics simulation method was employed to investigate the micro-separation mechanism of hydrogen purification using multi-walled carbon nanotubes (MWNTs) and hydrogen-bonded organic frameworks (HOFs) as membrane materials. Novel composite membranes combining different HOF and MWNT materials were designed to enhance the interaction energy with CO2. The results demonstrated that these composite membranes exhibited higher selectivity in the separation of H2/CO2 gas mixtures, achieving higher hydrogen permeability compared with individual HOF and MWNT membranes. Notably, the PhTCz1 + CNT, UPC-H4a + CNT, and TCPP-1,3-DPP + CNT-3 composite membranes demonstrated 100 % CO2 retention and reached a maximum flux hydrogen of 4.782 × 105 GPU, which was higher than traditional membranes by 6 orders of magnitude. Furthermore, the PhTCz1 + CNT-3 composite membrane had a significant ability to simultaneously intercept CO2 and CO. The MD calculation results show that this newly synthesized HOF + CNT composite membrane material can provide high permeability as well as ultrahigh selectivity simultaneously, making it a prospective H2 separation membrane with superior performance.