Decoupling Hydrogen Evolution From Continuous Irradiation via CO₂-Mediated Proton-Coupled Electron Storage

The intermittent nature of solar energy and the safety concerns of high-pressure hydrogen storage/transportation pose critical challenges to the widespread adoption of solar-driven hydrogen production. To address these challenges, we explored a metal-organic framework/polymeric carbon nitride (PCN) heterostructure with atomically dispersed Cu sites (Cu@MOF/PCN-n, n = 1-5, representing the initial mass percent of Cu@MOF-303 as 1%-5%). The optimized Cu@MOF/PCN-3 enables solar energy storage and decouples H₂ evolution from continuous irradiation through CO₂-mediated proton-coupled electron storage. Under CO₂ atmosphere, Cu@MOF/PCN-3 demonstrates exceptional photoelectron storage capabilities under illumination and achieves a remarkable H₂ production rate of 2.88 mmol g^-1 in the dark, 3.2-fold enhancement compared to Ar-controlled systems. Experimental and theoretical investigations demonstrate that CO₂ serves as a bifunctional electron-proton mediator, stabilizing photoelectrons via reversible carboxylation while facilitating proton transfer through *COOH intermediates, thereby decoupling H₂ evolution from continuous irradiation. The single Cu site plays a pivotal role in regulating electron extraction and proton coupling, effectively overcoming the thermodynamic competition between CO₂ reduction and hydrogen evolution reaction (HER). This work establishes a new paradigm for CO₂-mediated dark photocatalysis, offering a dual solution to overcome the critical challenges of solar intermittency and safe H₂ storage.