Bioinspired anion exchange membranes with dual steric cross-linking centers for industrial-scale water electrolysis

Abstract

OH⁻ transport through anion exchange membranes (AEMs) is influenced by the arrangement of ion channels. Inspired by the channel structure of pectin in plants, a precise molecular regulation approach has here been developed for designing high-performance AEMs. This approach utilizes two steric molecules, triptycene and 9,9′-spirobifluorene, as dual spatially cross-linking centers in AEMs. By incorporating both of these steric centers into poly(terphenyl piperidinium), the pore structure stability, ionic conductivity, and mechanical strength are further improved. This variant achieved a high OH⁻ conductivity of 197.4 mS cm⁻¹ and a significantly low swelling ratio of 8.6% at 80 °C. These characteristics enable the use of AEM water electrolysis (AEM-WE) for the achievement of a current density of 8.4 A cm⁻² at 2.0 V when using completely platinum group metal (PGM)-free catalysts. This device also demonstrated high performance by achieving a current density of 2.0 A cm⁻² at a cell voltage of 1.77 V at 60 °C, along with excellent stability (aging rate of 0.077 mV h⁻¹). It should be noted that an electrode cell based on a five-stacked-membrane, with a total flow-field area of 1250 cm², has been used in the present study. In addition, this cell device allowed for a current density of 20 000 A m⁻² at a cell voltage of 2.0 V. The molecular regulation approach developed here precisely represents a promising strategy for industrial applications of PGM-free AEM-WE systems.