Elucidating Light-Regulated H⁺/Zn²⁺ Partitioning Behavior in Photoassisted Zinc-Ion Batteries

Photoassisted aqueous zinc batteries provide a compact route to couple light input with electrochemical energy storage, but the ionic origin of light-enhanced capacity remains difficult to quantify because proton and zinc-ion storage pathways are strongly intertwined. Here, a self-supported Cu/Cu₂S nanoarray is used as a light-responsive conversion interface to resolve illumination-regulated H⁺/Zn²⁺ partitioning. By tuning proton accessibility through dimethylformamide, H₂O/dimethylformamide, and H₂O electrolyte matrices, the dominant charge carrier shifts from Zn²⁺-favored storage to nearly balanced H⁺/Zn²⁺ storage and then to H⁺-dominated storage. Illumination enlarges the cyclic voltammetry response by 110.2%, reduces polarization, and enables nearly 50% capacity enhancement at 5 A g^-1. State-resolved Raman spectroscopy, X-ray photoelectron spectroscopy, and ex situ X-ray diffraction reveal light-regulated ZnS/basic-zinc-salt evolution and improved Cu/S interfacial reversibility. These findings identify nanoscale Cu-S conversion interfaces as light-tunable platforms for directing proton-cation competition, offering a carrier-resolved design principle for photoassisted aqueous batteries.