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 repre-sented 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.