In situ ligand stripping of CeO2 nanocrystals in anion exchange membranes for enhanced water electrolysis

Abstract

Colloidal metal oxide nanocrystals offer advantages such as controllable size, shape, and doping, along with excellent solution dispersion, making them promising fillers for anion exchange membranes (AEMs). However, as-synthesized nanocrystals are typically capped with hydrophobic ligands, which limit water uptake and ion conductivity. Here, we address this challenge by employing in situ ligand stripping of highly dispersed CeO₂ nanocrystals within a polymer matrix. The ligand-capped nanocrystals are homogeneously distributed in quaternized poly(styrene-b-(ethylene-co-butylene)-b-styrene) (QSEBS) AEMs. Under alkaline conditions (1 M KOH), the ligands are removed in situ within the polymer matrix, transforming the nanocrystals from hydrophobic into hydrophilic. A 6 wt% loading of nanocrystals yields the highest OH⁻ conductivity (139.5 mS cm⁻¹ at 80 °C) and water electrolysis performance (2.52 A cm⁻² at 2 V at 50 °C). The composite membranes also exhibit enhanced alkaline/oxidation stability and mechanical properties, attributed to the stripped CeO₂ nanocrystals. Our study provides new insights into the design of mixed matrix AEMs through in situ ligand stripping of highly dispersed nanocrystals.