Constructing Mo⁵⁺ sites in molybdenum oxide by lattice stress for efficient ammonia synthesis

Molybdenum oxide (MoO₃) is a promising catalyst for electrocatalytic nitrogen reduction (eNRR). However, Mo sites with saturated coordination are not favorable to stable N₂ adsorption. Herein, we employed sodium ions as electron donors to interact with the interlayer atoms of MoO₃, causing localized lattice stress on it and weakening the M-O bond, thus inducing the Mo⁵⁺ active sites (Na_xMoO₃). The N₂ temperature-programmed desorption (N₂-TPD) result of the as-prepared Na_xMoO₃ exhibits that introducing Mo⁵⁺ could significantly improve the N₂ adsorption on the catalyst's surface. The optimized Na_xMoO₃ has an NH₃ yield of 41.3 μg h⁻¹ mg⁻¹ at ambient temperature and an FE of 21.4 %, which is in the relatively advanced position in the contemporaneous studies. Both experiments and density-functional theory (DFT) calculation demonstrated that the Mo⁵⁺ sites can effectively reduce the d-orbital energy level of Mo, which significantly enhances the interaction with N₂.