Integrating Cooperative Dual Active Sites Onto a Plasmonic Photocatalyst for Synergistic Promotion of the Reduction and Oxidation Half‐Reactions in Ammonia Synthesis

ABSTRACT Photocatalytic N ₂ fixation offers a promising sustainable alternative to the energy‐intensive Haber–Bosch process. Since N ₂ fixation involves the reduction and oxidation half‐reactions, understanding their synergistic relationship and achieving their cooperation is crucial for improving the overall efficiency of N ₂ fixation. To fulfill this objective, we have designed a type of Ru‐WO _{3− x} /CoO _x photocatalyst with respective reduction and oxidation active sites. In this type of photocatalyst, Ru doping not only provides reduction sites to facilitate N ₂ adsorption and activation but also optimizes the band structure by widening the defect band and elevating the Fermi level. Meanwhile, the CoO _x clusters serve as O ₂ evolution sites that can accelerate hole utilization and improve electron–hole separation, thereby enhancing N ₂ reduction. Consequently, the Ru‐WO _{3− x} /CoO _x photocatalyst gives an impressive NH ₃ production rate of 131.95 µmol g ⁻¹ h ⁻¹ in pure water, superior to the photocatalysts with a single type of active site. The optimized catalyst delivers a solar‐to‐chemical conversion efficiency of 0.22% under AM 1.5G light illumination and maintains an apparent quantum efficiency above 0.2% within the entire test range, including the near‐infrared region. This work underscores the mutual influence of the oxidation and reduction half‐reactions in photocatalysis and highlights the cooperation between redox‐active sites.