Vacancy and N dopants facilitated Ti3+ sites activity in 3D Ti3-xC2Ty MXene for electrochemical nitrogen fixation

Identification of the intrinsic active sites and understanding of the kinetics processes on electrocatalysts is essential in the rational design of highly efficient electrochemical nitrogen fixation electrocatalysts. In this work, 3D N-doped-Ti-V-Ti3-xC2Ty-1.2 MXene was fabricated for ENRR. The intrinsic active-site, as well as the activated mechanism of 3D porous N-doped Ti3-xC2Ty MXene, were elucidated by in situ electrochemical Raman spectrum and DFT simulation. It was demonstrated that the Ti3+ species were the intrinsic active sites for electrocatalytic nitrogen reduction reaction (ENRR), and the electronic state of the active Ti3+ species in 3D porous N-doped Ti3-xC2Ty MXene can be adjusted by surface atomic engineerings, such as vacancy creation and heteroatom doping. The introduction of Ti vacancies can trap the electrons that inject into an antibonding orbital of adsorbed N-2, which facilitates the activation of N-2. Besides, the N-dopant species in the MXene can not only act as steady active sites for ENRR but also promote the desorption of NH3 by minimize the orbits overlap between Ti3+ and N-2, which was confirmed by a bidirectional isotopic exchange labeling method and DFT simulation. This finding paves a valuable strategy for the surface engineering design of efficient catalysts in ENRR.

Automated summary

This study demonstrated that Ti3+ species are the intrinsic active sites for ENRR, and the electronic state of active Ti3+ species can be adjusted by surface atomic engineerings in 3D porous N-doped Ti3-xC2Ty MXene. In addition, Ti vacancies can facilitate the activation of N-2, while N-dopant species in MXene can act as stable active sites and promote NH3 desorption by reducing the orbital overlap between Ti3+ and N-2.