Decoupling Hydrogen Evolution From Continuous Irradiation via CO ₂ ‐Mediated Proton‐Coupled Electron Storage

ABSTRACT 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 H 2 evolution from continuous irradiation through CO 2 ‐mediated proton‐coupled electron storage. Under CO 2 atmosphere, Cu@MOF/PCN‐3 demonstrates exceptional photoelectron storage capabilities under illumination and achieves a remarkable H 2 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 CO 2 serves as a bifunctional electron‐proton mediator, stabilizing photoelectrons via reversible carboxylation while facilitating proton transfer through *COOH intermediates, thereby decoupling H 2 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 CO 2 reduction and hydrogen evolution reaction (HER). This work establishes a new paradigm for CO 2 ‐mediated dark photocatalysis, offering a dual solution to overcome the critical challenges of solar intermittency and safe H 2 storage.