S‐Scheme Charge Separation Enables Photocarrier‐Regulated Aqueous NH 4 + Storage in g‐C 3 N 4 @WO 3 Heterojunctions

ABSTRACT Aqueous ammonium‐ion (NH 4 + ) batteries are promising for sustainable energy storage, yet their performance is severely constrained by sluggish reaction kinetics. Photo‐assisted strategies offer a compelling route to overcome these limitations; however, single‐semiconductor electrodes suffer from rapid photogenerated carrier recombination, resulting in poor light‐utilization efficiency. Here, we develop a g‐C 3 N 4 @WO 3 S‐scheme heterojunction (CNW) that unlocks efficient light‐to‐charge conversion for photocarrier‐regulated reversible NH 4 + storage. Characterization and simulation reveal that Fermi level alignment and band bending at the CNW interface establish a built‐in electric field, driving S‐scheme charge separation with selective recombination of low‐energy carriers and retention of high‐energy electrons on g‐C 3 N 4 and holes on WO 3 . This preserves strong redox capability, thereby enabling efficient utilization of photoexcited carriers in the electrochemical storage process. Together with pronounced interfacial orbital coupling, the resulting photocarrier redistribution accelerates NH 4 + adsorption and electron/ion transport. Consequently, the CNW electrode delivers a 187% capacity enhancement under illumination, achieving 452 mAh g −1 at 2 A g −1 with excellent cycling stability, surpassing all currently reported W‐based and C‐based materials for NH 4 + storage. Correlative electrochemical, spectroscopic, and theoretical analyses decouple photoelectric and thermal effects, revealing a photoelectric‐dominated, thermally assisted synergistic mechanism that simultaneously enhances NH 4 + storage kinetics and capacity.