Metal-organic frameworks with surface-grafted azobenzene for energy storage
This study addresses the intermittent nature of solar energy by developing a dual-mode energy storage material. A bulky azobenzene derivative, 4’-aminoazobenzene-4-sulfonic acid (AABS), was grafted onto the surface of ZIF-90, yielding ZIF-90-AABS (ZIF-AABS). The surface template effect enables reversible cis-trans isomerization of AABS, achieving photochemical energy storage of 5.1 J g−1. Because AABS is confined to the surface, ZIF-AABS retains the crystalline porous structure of ZIF-90, allowing encapsulation of octadecyl alcohol (OD) as a phase change material (PCM). The resulting composite, OD/ZIF-AABS, exhibits a latent heat storage capacity of 121.3 J g−1 at maximum OD loading, with no significant degradation after 50 melting/solidifying cycles. This work demonstrates a synergistic approach that combines photochemical and phase-change energy storage within a single MOF-based platform, expanding the application scope of azobenzene and MOF composites for solar energy storage.