Abstract:
The density of states (DOS) , Gibbs free energy (Δ
G)of the reaction intermediate structure, charge density difference (CDD), work function and activation energies (
Ea) of the reaction intermediate structure on the surface of two-dimensional transition metal carbon nitride (MXenes) Ti
2CT
2 and Ti
3C
2T
2 (T=O* or OH*) catalysts before and after N
2 adsorption were calculated by first-principles, to explore the new mechanism of N
2 reduction reaction (NRR) 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 not conducive to NRR due to high
ηNRR. While Ti
2C(OH)
2 and Ti
3C
2(OH)
2 surfaces can provide H atoms during the initial adsorption step and undergo NRR through the Enzymatic mechanism, with the corresponding
ηNRR decreasing to 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 hybridization intensity of N 2p and O 2p orbitals on the surface of *OH terminal and *O terminal is different, resulting in different NRR activity of OH* MXene. Therefore, it is believed that N
2 is adsorbed on Ti
2C(OH)
2 and Ti
3C
2(OH)
2 via “N
2+2*H=*N
2H
2” , followed by NRR along the Enzymatic mechanism.