Heterogeneous metal trimer catalysts on Mo2TiC2O2 MXene for highly active N2 conversion to NH3

Activating the inert basal plane of functional-group-terminated MXenes is highly desirable for non-noble metal MXenes applied for the N2 reduction reaction (NRR) to value-added ammonia (NH3), but remains a significant challenge. Herein, we report the coupled interactions and catalytic mechanism of the supported trimeric metal M3 single-cluster catalysts (SCCs) on oxygen-vacancy-rich Mo2TiC2O2 (VO−Mo2TiC2O2) MXene materials for catalyzing this difficult reaction via spin-polarized density functional theory (DFT) calculations. Energy and electronic property analysis showed that the robust structural stability of the M3/VO−Mo2TiC2O2 catalysts stemmed from the vacancy defects, electronegativity difference, and significant charge redistribution. Based on the unique bidirectional electron transfer activation mechanism, the N2 adsorption strength can be well represented by a simple descriptor of the valence electrons in the d orbitals of M3 trimers. Remarkably, these confined Rh3, Ru3, Ni3 and Co3 SCCs on VO−Mo2TiC2O2 were capable of providing superior electrocatalytic activity and selectivity toward the NRR with ultra-low limiting potentials of −0.23, −0.32, −0.42 and −0.44 V, respectively. Finally, a mechanistic investigation illustrated that the valence electrons, charge transfer, and d-band center of the M3 active sites could collectively act as good descriptors to correlate the structure and NRR activity.