Photocatalytic ammonia synthesis from nitrate reduction on nickel single-atom decorated on defective tungsten oxide

Photocatalytic reduction of waste nitrate (NO3- ) into value-added ammonia (NH3) under ambient conditions has enormous advantages over the Haber-Bosch process. However, weak adsorption capacity and low efficiency of photocatalysts limit its large-scale application. Here, Ni single-atom (SA) on defective WO3 (Ni/HxWO3_y) hybrids with abundant oxygen vacancies (OVs) are synthesized by a facile H-spillover process, which exhibits a high NH3 rate of 10.5 mmol gcat-1 h-1 and 98.26 % NH3 selectivity. In situ characterizations and theoretical calculations demonstrate the activity mainly derives from the synergetic effect of OVs and Ni SAs. That is, (1) photogenerated electrons and adsorbed NO3- transfer from OVs to Ni SAs; (2) the strong hybridizations of Ni 3d O 2p orbitals of NO3- accelerate electron transfer from Ni SAs to NO3- ; (3) Ni SAs effectively reduce the free energy of the rate-limiting step (NO2* -> NO*) of HxWO3_y. In simulated wastewater, the durable performance of Ni/ HxWO3_y hybrids proves great potential in industrial applications.