Single Ru-N₄ Site-Embedded Porous Carbons for Electrocatalytic Nitrogen Reduction

Ammonia is an effective feedstock for chemicals, fertilizers, and energy storage. The electrocatalytic nitrogen reduction reaction (NRR) is an alternative, efficient, and clean technology for ammonia production, relative to the traditional Haber-Bosch method. Single-metal catalysts are widely studied in the field of NRR. However, very limited conclusions have been made on how to precisely modulate the coordination environment of the single-metal-atom sites to boost catalytic NRR performance. Herein, we report a 5,7-membered carbon ring-involved porous carbon (PC) preparation toward single-atom Ru-embedded PCs. As electrocatalysts, such materials exhibit surprisingly promising catalytic NRR properties with an NH₃ yield rate of up to 67.8 ± 4.9 μg h^-1 mg_cat^-1 and a Faradaic efficiency of 19.5 ± 0.6%, exceeding those of most of the reported single-atom NRR catalysts. Extended X-ray absorption fine structure demonstrates that the presence of topological defects increases the Ru-N bond from 1.48 to 1.56 Å, modulating the coordination environment of the single-atom Ru active sites. Density functional theory-calculated results demonstrate that the adsorption of N₂ onto single-atom Ru surrounded by topological defects extends the N≡N bond to 1.146 Å, weakening the strength of N≡N and making it susceptible to the NRR. All in all, this work provides a new design strategy by involving topological defects and corresponding large polarization around the Ru single atom to boost the catalytic NRR performance. Such a concept can also be applied to many other kinds of catalysts for energy storage and conversion.