Sp/sp2 carbon ratio-driven high-throughput screening of electrocatalytic nitrogen reduction performance on transition metal single-atom catalysts

Single-atom catalysts (SACs) have been widely utilized in electrochemical nitrogen reduction reactions (NRR) due to their high atomic utilization and selectivity. Owing to the unique sp/sp2 co-hybridization, graphyne materials can offer stable adsorption sites for single metal atoms. To investigate the influence of the sp/sp2 hybrid carbon ratio on the electrocatalytic NRR performance of graphyne, a high-throughput screening of 81 catalysts, with 27 transition metals loaded on graphyne (GY1), graphdiyne (GY2), and graphtriyne (GY3), was conducted using first-principles calculations. The results of the screening revealed that Ti@GY3 exhibits the lowest energy barrier for the rate-determining step (0.32 eV) in NRR. Further, to explore the impact of different sp/sp2-hybridized carbon ratios on the catalytic activity of SACs, the mechanism of nitrogen (N2) adsorption, activation, and the comprehensive pathway of NRR on Ti@GY1, Ti@GY2, and Ti@GY3 was systematically investigated. It was found that the ratio of sp/sp2-hybridized carbon can significantly modulate the d-band center of the metal, thus affecting the energy barrier of the rate-determining step in NRR, decreasing from Ti@GY1 (0.59 eV) to Ti@GY2 (0.49 eV), and further to Ti@GY3 (0.32 eV). Additionally, the Hall conductance was found to increase with the bias voltage in the range of 0.4–1 V, as calculated by Nanodcal software, demonstrating an improvement in the conductivity of the SAC. In summary, this work provides theoretical guidance for modulating the electrocatalytic nitrogen reduction activity of SACs by varying the ratio of sp/sp2 hybrid carbon, with Ti@GY3 showing potential as an excellent NRR catalyst.