S-Scheme Charge Separation Enables Photocarrier-Regulated Aqueous NH4 + Storage in g-C3N4@WO3 Heterojunctions.

Aqueous ammonium-ion (NH4 +) 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-C3N4@WO3 S-scheme heterojunction (CNW) that unlocks efficient light-to-charge conversion for photocarrier-regulated reversible NH4 + 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-C3N4 and holes on WO3. 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 NH4 + 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 NH4 + storage. Correlative electrochemical, spectroscopic, and theoretical analyses decouple photoelectric and thermal effects, revealing a photoelectric-dominated, thermally assisted synergistic mechanism that simultaneously enhances NH4 + storage kinetics and capacity.