Mo₂C-MoO₂ Heterostructure Quantum Dots for Enhanced Electrocatalytic Nitrogen Reduction to Ammonia

The electrocatalytic nitrogen reduction reaction (NRR) has been regarded as a promising strategy for producing ammonia (NH₃) at ambient conditions. However, the development of the NRR is severely hindered by the difficult adsorption and activation of N₂ on the catalyst surface and the competitive hydrogen evolution reaction (HER) due to the lack of efficient NRR electrocatalysts. Herein, Mo₂C-MoO₂ heterostructure quantum dots embedded in reduced graphene oxide (RGO) are proposed as efficient catalysts for the electrocatalytic NRR. The ultrasmall size of the quantum dot is beneficial for exposing the active sites for the NRR, and the synergetic effect of Mo₂C and MoO₂ can promote N₂ adsorption and activation and suppress the competitive HER simultaneously. As a result, a well-balanced NRR performance is achieved with a high NH₃ yield rate of 13.94 ± 0.39 μg h⁻¹ mg⁻¹ at -0.15 V vs RHE and a high Faradaic efficiency of 12.72 ± 0.58% at -0.1 V vs RHE. Density functional theory (DFT) calculations reveal that the Mo₂C (001) surface has a strong N₂ adsorption energy of -1.47 eV with the side-on configuration, and the N≡N bond length is elongated to 1.254 Å, indicating the enhanced N₂ adsorption and activation on the Mo₂C surface. On the other hand, the low ΔGH* for HER over the MoO₂ (-111) surface demonstrates the impeded HER process for MoO₂. This work may provide effective catalyst-design strategies for enhancing the electrocatalytic NRR performance of Mo-based materials.