Abstract:
The hydrogenation mechanisms of N
2 reduction reaction (NRR) on Ti
2CT
2 and Ti
3C
2T
2 (T=O* or OH*) MXenes are studied by first-principles study. And the DOS of N
2 adsorption, the Gibbs free energy of the reaction intermediate structure (Δ
G), charge density difference(CDD), work function and activation energies (
Ea) are calculated to explore the new mechanism of NRR reaction on the surface of OH * terminal MXene. The results show that N
2 undergoes physical adsorption on Ti
2CO
2 and Ti
3C
2O
2 surfaces (∆
q≈0 e), while chemical adsorption occurs on Ti
2C(OH)
2 and Ti
3C
2(OH)
2 surfaces (∆
q>0.2 e), Ti
2CO
2 and Ti
3C
2O
2 are do not favor NRR due to high
ηNRR. While Ti
2C(OH)
2 and Ti
3C
2(OH)
2 can catalyze NRR by donating their surface H at initial steps and then via enzymatic mechanism, with the corresponding
ηNRR of 0.29 V and 0.38 V, respectively. Moreover, the calculated
ηNRR can be used as a function of
φ:
ηNRR=0.44
φ−0.71, where the correlation coefficient (
R2) is 0.97, showing a strong linear relationship between overpotential and work function. The strength and hybridization energy level of the N 2p orbitals and O 2p orbitals on Ti
n+1C
nT
2 and Ti
n+1C
n(OH)
2 are different during NRR, and delivering different catalytic activity for NRR. Finally, it concluded that the N
2 adsorption on Ti
2C(OH)
2 and Ti
3C
2(OH)
2 may via “N
2+2*H=*N
2H
2” at initial steps and then along enzymatic hydrogenation mechanism.