Metal-organic frameworks with surface-grafted azobenzene for energy storage

• • Photochemical energy storage of 5.1 J g−1 is achieved via reversible cis-trans isomerization of surface-grafted AABS on ZIF-90; this value represents a 100% increase over typical azobenzene-functionalized MOFs, enabling direct solar-to-chemical storage without phase change. • • The composite PCM OD/ZIF-AABS delivers a latent heat of 121.3 J g−1 at maximum OD loading, which is 15% higher than that of pure OD (105 J g−1), attributable to the confinement effect and improved thermal conductivity of the MOF scaffold. • • After 50 melting/solidifying cycles, the latent heat retention exceeds 98%, with no observable leakage or chemical degradation, indicating robust cycling stability essential for long-term industrial deployment in solar thermal systems. • • The surface grafting strategy preserves the BET surface area of ZIF-90 (>1000 m2 g−1) and pore volume, allowing high PCM loading (up to 70 wt%) while maintaining photochemical activity, a critical balance for dual-mode energy storage.