Supplementary material from "Using polarizable flexible force fields to design metal-organic framework-containing mixed matrix membranes for hydrogen purification from solar water splitting"

Abstract

In this study, mixed matrix membranes (MMMs) consisting of a continuous polymer phase and a dispersed metal-organic framework (MOF) phase were designed to purify hydrogen from the solar water splitting process. We first identified 20 MOFs with a small pore limiting diameter of ≤3 Å to restrict the passage of larger molecules such as N2 and O2, thereby allowing the smaller H2 molecule to pass through. These MOFs were assessed for water stability, thermal stability, solvent removal stability, and to identify open-metal sites. We developed atomistic polarizable flexible force fields for these 20 MOFs and used these in molecular dynamics and Monte Carlo simulations to calculate diffusion constants and adsorption isotherms. Using these results, we selected stable MOFs with the highest permeability and ideal selectivity for hydrogen separation. We used experimental data for polymer permeability and selectivity. Finally, we used the Maxwell model to predict the permeability and ideal selectivity of each MMM. We observed that selectivity is primarily governed by polymer properties, and permeability increases by adding MOFs as the dispersed phase. Our computed results showed that MMMs have approximately a twofold reduction in required membrane area compared with pure polymers. TPBO-1.0/ARIBOS performed the best, requiring the smallest membrane area.