A Plasmonic S‐Scheme Heterojunction Achieves Broadband Response and Ultralow Overpotential of Photo‐Assisted Li─O 2 Batteries

Li─O 2 batteries (LOBs) offer an ultrahigh theoretical energy density but suffer from a large overpotential. Photocathodes can lower this overpotential, but most of them cannot achieve efficient charge separation, sufficient redox capability, and broadband photoresponse at the same time. Here, a plasmonic S‐scheme heterojunction photocathode (W 18 O 49 / g ‐C 3 N 4 , WOCN) is constructed. W 18 O 49 serves as the oxidation semiconductor of the heterojunction and a noble‐metal‐free plasmonic absorber, forming a continuous plasmonic heterointerface with g ‐C 3 N 4 . The intrinsic localized surface plasmon resonance (LSPR) of W 18 O 49 originates from periodically arranged lattice‐localized electrons in W 5+ clusters. Photogenerated carriers with strong redox capability and LSPR‐generated hot electrons are separated by the S‐scheme carrier transfer pathway. Under AM 1.5G illumination, the WOCN‐based LOBs exhibit an ultralow overpotential of 0.04 V and a round‐trip efficiency of 98.75%. Even under NIR illumination, an overpotential of 0.34 V and a round‐trip efficiency of 90.12% are achieved, demonstrating an effective NIR response in photo‐assisted LOBs for the first time. This work opens a new avenue for designing plasmonic S‐scheme heterojunctions toward next‐generation energy storage systems with full solar spectrum utilization.