Synergy of Photogenerated Electrons and Holes toward Efficient Photocatalytic Urea Synthesis from CO₂ and N₂

Abstract

Directly coupling N₂ and CO₂ to synthesize urea by photocatalysis paves a sustainable route for urea synthesis, but its performance is limited by the competition of photogenerated electrons between N₂ and CO₂, as well as the underutilized photogenerated holes. Herein, we report an efficient urea synthesis process involving photogenerated electrons and holes in respectively converting CO₂ and N₂ over a redox heterojunction consisting of WO₃ and Ni single-atom-decorated CdS (Ni₁-CdS/WO₃). For the photocatalytic urea synthesis from N₂ and CO₂ in pure water, Ni₁-CdS/WO₃ attained a urea yield rate of 78 μM h^-1 and an apparent quantum yield of 0.15 % at 385 nm, which ranked among the best photocatalytic urea synthesis performance reported. Mechanistic studies reveal that the N₂ was converted into NO species by ⋅OH radicals generated from photogenerated holes over the WO₃ component, meanwhile, the CO₂ was transformed into *CO species over the Ni site by photogenerated electrons. The generated NO and *CO species were further coupled to form *OCNO intermediate, then gradually transformed into urea. This work emphasizes the importance of reasonably utilizing photogenerated holes in photocatalytic reduction reactions.