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-TiV-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 N2, which facilitates the activation of N2. 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 N2, 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.