Two-dimensional C2N-based single-atom catalyst with complex microenvironment for enhanced electrochemical nitrogen reduction: A descriptor-based design

The catalytic descriptor with operational feasibility is highly desired towards rational design of high-performance catalyst especially the electrode/electrolyte solution interface working under mild conditions. Herein, we demonstrate that the descriptor Ω parameterized by readily accessible intrinsic properties of metal center and coordination is highly operational and efficient in rational design of single-atom catalyst (SAC) for driving electrochemical nitrogen reduction (NRR). Using two-dimensional metal (M)-BxPySzNm@C2N as prototype SAC models, we reveal that *N2 + (H+ + e−) → *N2H acts predominantly as the potential-limiting step (PLS) of NRR on M-B2P2S2@C2N and M-B1P1S1N3@C2N regardless of the distinction in coordination microenvironment. Among the 28 screened M active sites, with Ω values close to the optimal 4, M-B2P2S2@C2N (M = V (Ω=3.53), Mo (Ω=5.12), W (Ω=3.92) and M-B1P1S1N3@C2N (M = V (Ω=3.00), Mo (Ω=4.34), W (Ω=3.32) yield the lowered limiting potential (UL) as −0.45, −0.54, −0.36, −0.58, −0.25, and −0.24 V, respectively, thus making them the promising NRR catalysts. More importantly, these SACs are located around the top of volcano-shape plot of UL versus Ω, re-validating Ω as an effective descriptor for accurately predicting the high-activity NRR SACs even with complex coordination. Our study unravels the relationship between active-site structure and NRR performance via the descriptor Ω, which can be applied to other important sustainable electrocatalytic reactions involving activation of small molecules via σ-donation and π*-backdonation mechanism.