Influence of Sulfonic Acid Group on Sulfonated Polyethersulfone Membrane for PEM Fuel Cell: A First‐Principles Study

The introduction of a protogenic group such as sulfonic acid allows the operation of polymer electrolyte membranes for fuel cells at intermediate temperature (>100 °C) and very low humidity. A sulfonated polyethersulfone (SPES) membrane with additional sulfonation was simulated by density functional theory calculations to determine the beneficial effect of the sulfonic group, which induces hydrophilicity for increased hydrogen conductivity. A higher degree of sulfonation enhances the H 2 O adsorption. In particular, trans ‐di‐SPES ( trans ‐DSPES), with higher charge transfer to H 2 O and more hydrogen bonds, is more favorable for H 2 O adsorption than cis ‐DSPES; this is attributed to its narrow band gap (2.84 eV) and high adsorption energy (−0.81 eV) compared to cis ‐DSPES (2.96 and −0.69 eV, respectively). Theoretical findings suggest that adding the sulfonic acid group ultimately yields greater H 2 O adsorption on DSPES, increasing the hydrophilicity.