TiO2-Mo2C Heterostructure for Enhanced Electrocatalytic Nitrogen Reduction to Ammonia.

Abstract

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.