Macromolecule crosslinked hydroxide exchange membranes with low ammonia crossover for direct ammonia fuel cells

Abstract

Ammonia crossover in hydroxide exchange membrane (HEM) poses a significant challenge to the advancement of low-temperature DAFCs. In this study, we have developed two types of macromolecule crosslinked HEMs (PNH-ene-x and PNH-yne-x) through a straightforward in-situ thermal crosslinking method using alkenes and aromatic crosslinked moieties. The engineered crosslinked networks demonstrate dual functionality: effectively limiting water absorption to suppress ammonia permeation (2.62 × 10⁻⁷ cm² s⁻¹ for PNH-ene-2%) while maintaining a well-defined microphase-separated morphology to promote hydroxide ion conduction (45.1 mS cm⁻¹ at 30 °C). PNH-ene-2% achieves a superior membrane selectivity (9.57 × 10⁷ mS s cm⁻³) through optimal balance between transport properties and structural stability. Accordingly, the DAFC with PNH-ene-2% exhibits a high cell energy efficiency (26.9%) and a modest peak power density (256.8 mW cm⁻²), representing the best record for low-temperature DAFCs to date. This work suggests that crosslinking is an effective approach to prepare high-performance HEMs for low-temperature DAFCs.