Constrained-Unconstrained Strategy Empowers Metastable Assemblies to Achieve Breakthrough Enhancement in Photocatalytic Hydrogen Evolution Efficiency

Abstract

Solar photocatalytic hydrogen production represents a significant development direction within the clean energy sector. Whilst symmetric organic photocatalysts offer advantages such as abundant raw materials and tunable structures, their high exciton binding energy (Eb) severely constrains the conversion efficiency from solar to hydrogen energy. This study employs 3,9-pyridinedicarboxylic acid (PDA) as a model molecule, proposing an entrapment-release engineering strategy: PDA is confined within the interlayer space of layered double hydroxides (LDH), inducing the formation of a metastable stacked structure. Upon deconfinement, this structure persists to form a supramolecular assembly (SSA). This approach generates a dipole moment exceeding 20 Debye for PDA tetramers, with internal electric field intensities tenfold higher than crystalline structures. The ionisation energy Eb drops below 50 meV. Interfacial water molecules stabilise the supramolecular assembly via hydrogen bonding, yielding a water contact angle below 30° and enhancing surface reactions. Under visible light irradiation, the optimised SSA achieves a hydrogen evolution rate of 42.83 mmol·g–1·h–1, significantly surpassing most organic photocatalysts. This study transforms molecular symmetry from a limiting factor into a tunable parameter, establishing a novel paradigm for organic photocatalyst design.