Engineering graphyne-supported single-atom catalysts for efficient nitrogen reduction to ammonia: First-principles investigation.

The electrochemical nitrogen reduction reaction (N₂RR) offers a sustainable route to ammonia production under ambient conditions but remains limited by inert N ≡ N bond activation and competitive hydrogen evolution reaction (HER). Herein, we employ first-principles density functional theory (DFT) to systematically investigate the N₂RR activity of graphyne (GY) doped with single-atom transition metals (Fe, Mo, Ru, W). Structural analysis reveals strong binding and minimal distortion of the TM dopants on the porous, π-conjugated GY scaffold, with Fe-GY and W-GY exhibiting the highest stability. TM doping induces substantial bandgap narrowing and introduces localized d-orbital states near the Fermi level, enhancing charge transfer and catalytic potential. Adsorption studies show that TM sites effectively activate N₂ via π-backdonation, with W-GY inducing the greatest N ≡ N bond elongation. Free energy profiles demonstrate that TM-GY catalysts significantly lower the limiting potential for N₂RR compared to pristine GY, with Fe-Gy and W-GY achieving the most favorable limiting potential via the alternating mechanism. HER analysis reveals Ru-GY possesses near-optimal hydrogen adsorption energy (ΔG_H = -0.25 eV), suggesting high activity but possible competition with N₂RR. In contrast, Mo-GY and W-GY exhibit stronger H binding, potentially suppressing HER and improving N₂RR selectivity. This work identifies TM-doped GY as a versatile platform for single-atom catalysis and offers design principles for optimizing selectivity and efficiency in electrochemical nitrogen fixation.