From Dark Photocatalysis to Photobattery‐Type Operation: A Re‐Functionalized Ti‐MOF for Solar Energy Storage

ABSTRACT Efficient harvesting, storage, and on‐demand release of solar energy are essential for overcoming the intermittency of sunlight and enabling continuous solar energy‐driven processes, yet achieving storage of photogenerated charge remains challenging. Here, we report a Ti‐based bipyridine MOF, COK47‐bpy, and its ReCl(CO) 3 ‐functionalized analogue, ReCl47‐bpy , as photochargeable materials for time‐decoupled solar energy utilization. Re incorporation introduces localized photosensitizing and “electron sink” sites while preserving the parent framework structure, enabling visible‐light response, faster charge accumulation, and improved charge retention. In colloidal suspension, ReCl47‐bpy reaches an electron storage capacity of 19.5 C g −1 MOF under simulated solar irradiation and retains about 70% of the stored charge after 2.5 months. The stored electrons can be released on demand for dark hydrogen (H 2 ) evolution with electron‐to‐H 2 efficiencies exceeding 90%. Beyond colloids, when fabricated as robust FTO‐supported layers, ReCl47‐bpy |FTO photoelectrodes deliver capacities of up to ∼7.0 mAh g −1 MOF upon photocharging under 1 Sun irradiation. Overall, this work establishes Re‐functionalized Ti‐MOFs as versatile platforms for solar‐driven charge storage, dark photocatalysis, and MOF‐based photoelectrodes, toward the development of next‐generation MOF‐based energy devices.