Nitrogen-activation and charge-transfer lanthanide oxide promoters for enhanced photocatalytic ammonia synthesis

Abstract

Lanthanide metals possess multiple oxidation states, and are emerging as a frontier in nitrogen fixation, yet the knowledge regarding their photocatalytic mechanism and active sites is very limited. Herein, a series of LnO_y/MoS₂ (Ln = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu) photocatalysts for nitrogen fixation were successfully designed and synthesized. The experimental results demonstrate that the load of LnO_y redox promoters (Ln = Ce, Eu or Tb, the same hereinafter) significantly increases the effective reaction-active sites and promotes the separation and transfer of carriers, thereby enhancing photocatalytic performance. The visible-light-driven nitrogen fixation activities of LnO_y/MoS₂ composites are significantly enhanced, achieving remarkable rates of 342.8 μmol g⁻¹ h⁻¹ for CeO_y/MoS₂, 369.1 μmol g⁻¹ h⁻¹ for EuO_y/MoS₂, and 457.3 μmol g⁻¹ h⁻¹ for TbO_y/MoS₂, which are substantially higher than that of pristine MoS₂ (46.1 μmol g⁻¹ h⁻¹). Theoretical calculations reveal that LnO_y loading promotes the adsorption and activation of N₂ molecules, with the Tb site exhibiting the strongest adsorption capacity (ΔG = 1.46 eV) and superior electron transfer efficiency, as confirmed by PL spectroscopy and photocurrent response analysis. This work provides fundamental insights into the role of lanthanide oxides in regulating photocatalytic nitrogen activation and offers a strategic framework for designing high-performance lanthanide-based catalysts.