Atomic-Level Interfacial Regulation Enables Efficient Chlorine Redox Chemistry in Rechargeable H₂─Cl₂ Batteries

Hydrogen─chlorine (H₂─Cl₂) batteries are attractive high-power energy storage systems but remain fundamentally limited by inefficient Cl₂ confinement and sluggish interfacial Cl₂/Cl^- redox kinetics. Here, we report a hydrogen-bonded porphyrin framework with atomically dispersed Cu sites (SACu-GTUB5) that enables efficient Cl₂ storage and accelerates Cl₂/Cl^- conversion. The intrinsic porosity of the framework combined with chemically active Cu─N₄ centers enables synergistic physical confinement and chemical adsorption of Cl₂, effectively suppressing Cl₂ escape and improving Coulombic efficiency. As a result, the SACu-GTUB5-based H₂─Cl₂ battery exhibits stable operation across a wide temperature range (-40°C to 60°C) and achieves a high areal discharge capacity of 2.55 mAh cm^-2 over 300 cycles. Spectroscopic analyses combined with density functional theory calculations reveal that Cu─N₄ sites govern Cl₂ adsorption, electron redistribution, and reaction pathways, substantially lowering the energy barriers for Cl₂ reduction. This work establishes an atomic-level interfacial regulation strategy for controlling halogen redox chemistry in electrochemical energy storage.