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 (NaxMoO3). The N2 temperature-programmed desorption (N2-TPD) result of the as-prepared NaxMoO3 exhibits that introducing Mo5+ could significantly improve the N2 adsorption on the catalyst’s surface. The optimized NaxMoO3 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. [Display omitted] •More Mo5+ active sites were introduced in NaxMoO3 by Na intercalation.•DFT calculations indicate that introducing Mo5+ sites leads to more strong d-π* interaction, thus boosting N2 activation.•In situ FTIR spectroscopy confirmed the evolution of N2 on NaxMoO3 catalyst.•NaxMoO3 exhibited significantly improved eNRR performance.