Promoting activation of N2 and H2O via dual active sites synergistically for efficient photocatalytic ammonia synthesis

Abstract

Photocatalytic nitrogen fixation is a green synthetic process for the direct conversion of N₂ and H₂O to ammonia using solar energy. However, the scarcity of N₂ and H₂O active sites is a limiting factor in the kinetics of nitrogen fixation reactions. The construction of spatially synergistic dual active sites is a feasible strategy to overcome this challenge. Herein, Fe-doped CdS (FCS) photocatalysts containing S vacancy have been prepared by a simple one-step solvothermal method. The results show that S vacancy in FCS preferentially adsorb H₂O molecules and activate them to active hydrogen (H*) for nitrogen reduction. Fe sites tend to adsorb N₂ molecules and promote the d− band center of CdS to move to Fermi level (E_f), which significantly improves the activation ability of N₂ molecules. The unique dual active sites greatly reduce Gibbs free energy of N₂ and H₂O activation and improve surface reaction kinetics of nitrogen reduction reaction. NH₄⁺ production rate of FCS reached 13.39 μmol · h⁻¹ without sacrificial reagent, which was 13.2 times higher than that of CdS. This study proves the significance of synergy between active sites for improving reaction efficiency and provides inspiration for the construction of dual active systems in photocatalytic nitrogen reduction.