NaBr-impregnated covalent organic framework aerogels for enhanced ammonia sorption and thermal energy storage

Abstract

Ammonia (NH3) is a hydrogen-rich, carbon-free molecule with significant potential for sustainable energy storage and environmental applications. However, developing sorbents with high adsorption capacity, rapid kinetics, and stable performance under cyclic conditions remains a challenge. In this study, a series of sodium bromide (NaBr)-impregnated covalent organic framework aerogels (NaBr@COFAs) were synthesized, exhibiting a hierarchical porous structure that provides high surface area and enables effective NaBr dispersion, enhancing NH3 adsorption performance. Among the synthesized samples, NaBr@COFA-1 demonstrated an exceptional NH3 adsorption capacity of 0.92 g/g at 6.1 bar and 20 degrees C, along with rapid adsorption kinetics and excellent cyclic stability over multiple adsorption-desorption cycles. Notably, this performance is significantly superior to that of pure NaBr, which suffers from volumetric expansion during sorption-desorption. Furthermore, NaBr@COFA-1 achieved a high working capacity of 0.82 g/g within a temperature range of 20 to 40 degrees C and a pressure of 6.1 bar, representing a 35.4 % improvement over conventional NaBr-imprignated sorbents. The enhanced performance is attributed to the synergistic interactions between NaBr and the COF aerogel matrix. Specifically, Na+ ions coordinate with NH3 molecules, while Br- ions enhance hydrogen bonding interactions. This unique combination prevents structural degradation and maintains high sorption efficiency. The NaBr@COFAs developed in this study offer a promising approach for efficient ammonia capture and thermal energy storage, with significant potential for sustainable energy applications.