Topologically Constrained Semi-IPN Architectures: A Synergistic Strategy toward High-Strength Hydrogel Membranes with Superior Proton Conductivity and Thermal Stability

Hydrogel membranes exhibit promising proton conductivity, but their low mechanical strength and poor water retention ability limit their application in proton exchange membrane fields. In this work, the strategic integration of chitosan into the covalently cross-linked PEI network created a semi-interpenetrating network (semi-IPN) architecture where linear chitosan chains permeate the matrix through hydrogen bonding and electrostatic interactions, forming physical cross-links that impose topological constraints. Benefiting from the distinctive structural synergy between chitosan and the hydrogel matrix, the fabricated semi-IPN rigid hydrogel demonstrated exceptional tensile strength (7.8 MPa, representing a 172.57% improvement over chitosan-free counterparts), superior water retention capability (70.726% water retention rate at 12 h, doubling that of neat PEI hydrogel membranes), outstanding proton conductivity (165.7 mS/cm, 1.33 times higher than pristine hydrogels), and excellent electrical stability under elevated temperatures (88.6% conductivity retention at 80 °C after 720 min and 71.28% retention at 100 °C). We believe that the development of semi-IPN hydrogels in this work holds significant implications for advancing proton exchange membrane research, particularly in addressing critical challenges related to durability and proton transport efficiency.