Title : Engineering out-of-equilibrium molecular assemblies via confinement for efficient solar hydrogen production
Abstract:
Photocatalytic hydrogen evolution (PHE) via solar energy represents a key pathway towards sustainable energy, yet the energy conversion efficiency of the symmetric organic photocatalyst 2,6-naphthalenedicarboxylic acid (NDA) is constrained by its elevated exciton binding energy (Eb). This study employs NDA as a model molecule and proposes a confinement- deconfinement strategy to address this issue. Confinement of NDA within the interlayer space of layered double hydroxides (LDHs) induces a 65° tilted stacking arrangement due to geometric mismatch, forcing NDA into a metastable state (deviating from thermodynamic equilibrium). Following delocalisation treatment, this metastable structure is preserved, leading to the formation of NDA-based supramolecular assemblies (SSA). The NDA tetramers within the SSA exhibit a dipole moment exceeding 20 Debye and an internal electric field (IEF) intensity tenfold that of crystalline NDA. This property reduces the activation energy (Eb) to 42.6 meV and enhances charge separation efficiency to 65.29%, representing a 6.38-fold increase over the crystal. Concurrently, interfacial water molecules stabilise the SSA structure via hydrogen bonding, reducing the water contact angle to 28.5° and accelerating surface reaction kinetics. Under visible light irradiation (λ ≥ 420 nm), the optimised SSA achieves a hydrogen evolution rate of 63.18 mmol·g–1·h–1, outperforming most reported organic photocatalysts. This strategy transforms NDA's molecular symmetry from a limiting factor into a tunable parameter, establishing a universal paradigm for organic photocatalyst design
Keywords: layered double hydroxides; supramolecular; photocatalysis; hydrogen evolution
