Screening of effective NRR electrocatalysts among the Si-based MSi2N4 (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) monolayers

Recently, Science reported a novel centimeter-scale monolayer film of MoSi2N4 synthesized by the chemical vapor deposition method (Science, 2020, 369, 670). Since Si atom has been recognized to be an active phase for N-2 fixation, in this paper, we systematically evaluate the catalytic performance in the electrochemical N-2 reduction reaction (NRR) on a series of MSi2N4 (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) monolayers, by means of density functional theory calculations. It is found that the N vacancy, which should be firstly created to expose the active Si atoms, is more favorably formed on a pre-hydrogenated surface. Through a three-step screening, TiSi2N4 and TaSi2N4 monolayers are predicted to be highly potential and promising electrocatalysts because they can (i) successfully capture N-2, (ii) effectively recover to the initial active states after a round of catalytic cycle without a strong surface reconstruction, and (iii) be stabilized at high temperatures. Moreover, thorough NRR mechanism investigations show that the NRR process proceeds via a Mars-van Krevelen mechanism, where the calculated limiting potentials are only -0.41 and -0.46 V for TiSi2N4 and TaSi2N4, respectively.

Automated summary

This study systematically evaluated the catalytic performance of a series of MSi2N4 monolayers in the electrochemical N-2 reduction reaction through density functional theory calculations, and identified TiSi2N4 and TaSi2N4 as highly potential and promising electrocatalysts. Thorough NRR mechanism investigations showed that the NRR process proceeds via a Mars-van Krevelen mechanism, with calculated limiting potentials of -0.41 and -0.46 V for TiSi2N4 and TaSi2N4, respectively.