Encapsulation of Phase-Changing Eutectic Salts in Magnesium Oxide Fibers for High-Temperature Carbon Dioxide Capture: Beyond the Capacity–Stability Tradeoff

Abstract

Eutectic mixture (EM)-promoted MgO sorbents exhibit high CO2 sorption capacities but experience a significant decrease in uptake after multiple sorption–regeneration cycles due to EM movement and redistribution at high temperatures. Encapsulation of a pseudoliquid, phase-changing EM promoter with MgO may thus prevent the loss of active interface by confining the EM within a fixed area inside a MgO shell. In this work, we successfully embedded an EM composed of KNO3 and LiNO3 in a MgO fiber matrix via core–shell electrospinning. The synthesized sorbent achieved relatively high and steady sorption capacities, maintaining a stable uptake of ∼20 wt % after 25 sorption–regeneration cycles. The sorbent was also characterized using various techniques including in situ transmission electron microscopy (TEM) to describe its morphology, from which it was confirmed that the eutectic salt existed in distributed hollow pockets within the MgO fiber matrix and stayed confined within these fixed areas, favorably limiting its movement and redistribution when exposed to high temperatures where it exists in the liquid form. The EM may also be described as a glue that holds the fiber together, while MgO acts as a protective shell that prevents structural changes and rearrangement caused by EM movement, allowing the sorbent to retain its cyclic stability after multiple cycles and demonstrating its potential for industrial use after further improvement. Thus, the microencapsulation of a phase-changing EM material with pure MgO metal oxide was successfully achieved and might be explored for various material applications.