Solar Energy Storage in Polyoxometalate for On‐Demand Hydrogen Transportation and Evolution

ABSTRACT Widespread application of solar‐driven hydrogen production is hindered by critical limitations: the inherent safety risks of high‐pressure H 2 storage/transport, and the intermittent nature of solar energy. To address these challenges, we develop a solar energy storage and on‐demand hydrogen production system by synergistically integrating commercial polyoxometalate (NH 4 ) 6 H 2 W 12 O 40 (W 12 ) with graphitic carbon nitride (g‐C 3 N 4 ). This system demonstrates remarkable efficiency in storing solar energy as electrons within W 12 during illumination. These stored electrons can be released on demand in the dark through Pt/C activation to produce H 2 , achieving a highly efficient hydrogen evolution rate of 3220 µmol g −1 h −1 under dark photocatalytic conditions. Notably, the system maintains robust performance under real‐world conditions, delivering an outdoor hydrogen evolution rate of 954 µmol g −1 h −1 under natural sunlight irradiation. Detailed analysis reveals an optimized electron storage‐release pathway, facilitated by the favorable alignment between the reduction potential of W 12 and the band structure of g‐C 3 N 4 , as well as the electrostatic self‐assembly driven by oppositely charged g‐C 3 N 4 and W 12 . In this system, solar energy is facilely stored as stabilized electrons within the POM‐semiconductor suspension, which can then be efficiently transported to light‐deficient environments and controllably released for on‐demand hydrogen evolution.