TiO₂-Mo₂C Heterostructure for Enhanced Electrocatalytic Nitrogen Reduction to Ammonia

The development of catalysts with high activity and selectivity for the electrochemical nitrogen reduction reaction (NRR) remains crucial. Molybdenum carbide (Mo₂C) shows promise as an electrocatalyst for NRR but faces challenges due to the difficulty of N₂ adsorption and activation as well as the competitive hydrogen evolution reaction. In this study, we propose a strategy of combining TiO₂ with Mo₂C to form heterostructure catalysts. Our first-principles theoretical calculations indicate that the TiO₂-Mo₂C heterostructure exhibits enhanced N₂ adsorption and activation, attributed to the increased interaction between the π_4d ^* orbital of Mo and the π_2p ^* orbital of N₂, facilitated by the directional modulation of Mo's d-orbitals by TiO₂. A more positive integrated crystal orbital Hamilton population and an elongated N≡N bond length prove this. Additionally, the higher Gibbs free energy for N₂ compared to that for H demonstrates a preference for N₂ adsorption. We further elucidate the catalytic mechanism for converting N₂ to NH₃ on the TiO₂-Mo₂C surface, identifying the associative distal pathway as the dominant route over the associative alternating pathway. This work highlights unique advantages of the TiO₂-Mo₂C heterostructure for the NRR and provides theoretical guidance for designing efficient NRR electrocatalysts.