Quantifying coordination effects for rational design of MXene-based NRR electrocatalysts

Abstract

The coordination environment of single-atom catalysts (SACs) on two-dimensional supports critically dictates their performance in the nitrogen reduction reaction (NRR), yet a unifying design principle remains elusive. Here, we decipher this structure–activity relationship by systematically investigating nine transition metals in two distinct configurations—doping versus anchoring—on Mo₂TiC₂O₂ MXene. We identify Mo- and Cr-doped systems as exceptional catalysts, exhibiting ultralow limiting potentials of 0.19 and 0.21 V, respectively. Our mechanistic analysis reveals a delayed activation effect, where the critical weakening of the NN bond occurs not upon initial adsorption but during the first hydrogenation step. This finding underscores that the overall activity is governed by the synergistic interplay between the metal and its coordination environment, rendering adsorption energies of single intermediates inadequate as descriptors. To overcome this limitation, we develop and iteratively refine an intrinsic descriptor, φ₃, which successfully unifies the activity trends across both doped and anchored configurations into a single volcano plot. This work provides a universal framework for the rational design of high-performance NRR SACs by harnessing the synergy between the metal center and its local coordination environment.