Synergy of Photogenerated Electrons and Holes toward Efficient Photocatalytic Urea Synthesis from CO 2 and N 2 .

Directly coupling N 2 and CO 2 to synthesize urea by photocatalysis paves a sustainable route for urea synthesis, but its performance is limited by the competition of photogenerated electrons between N 2 and CO 2 , as well as the underutilized photogenerated holes. Herein, we report an efficient urea synthesis process involving photogenerated electrons and holes in respectively converting CO 2 and N 2 over a redox heterojunction consisting of WO 3 and Ni single-atom-decorated CdS (Ni 1 -CdS/WO 3 ). For the photocatalytic urea synthesis from N 2 and CO 2 in pure water, Ni 1 -CdS/WO 3 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 N 2 was converted into NO species by ⋅OH radicals generated from photogenerated holes over the WO 3 component, meanwhile, the CO 2 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.