Theoretical and Comparative Analysis of Graphdiyne and Confined Flexible Nitrogen-Doped Graphdiyne-Supported Single-Atom Catalysts for Electrochemical Nitrogen Reduction

To develop high-performance and low-cost catalysts for electrochemical nitrogen reduction reaction (eNRR) in producing ammonia, a promising alternative to the Haber-Bosch process continues to be a substantial challenge. Herein, by using density functional theory calculations, single-atom-supported pristine and nitrogen-doped (N-doped) graphdiyne (GDY) monolayer-catalyzed eNRR were investigated to realize high performance via rational design. Candidate catalysts include 10 different transition-metal (M = Cr, Mn, Fe, Co, Ni, Cu, Mo, W, Re, and Ru) single-atom-anchored GDY monolayers (M1/GDY) and three different types of N-doped (sp2-N and sp-N) GDY monolayers (M1/ Nn-GDY, n = 1-3), with 40 single-atom catalysts (SACs). Both Mo1/N3-GDY and W1/N3-GDY were screened out with rather low theoretical onset potentials of merely -0.36 and -0.41 V, respectively. Further investigation of the exemplar Mo1/N3-GDY system shows that it has high selectivity, stability, and activity toward ammonia. The synergy effect between single-atom Mo and the confined flexibility substrate gives rise to self-adjustment of the coordination microenvironment of Mo1/N3-GDY, that is, this doped first coordination sphere sp-N is confined, yet shows steric flexibility, and transfers into sp2-N without Mo-N bond formation when single-atom Mo is anchored. Therefore, the system regulates adsorption pattern and strength of N2and intermediates, and finally boosts the performance. This work provides a new idea of using a confined flexibility substrate to construct SACs for efficient synthesis of ammonia at ambient conditions.