N,S coordination in Ni single-atom catalyst promoting CO 2 RR towards HCOOH.

Carbon-based single atom catalysts (SACs) are attracting extensive attention in the CO reduction reaction (CORR) due to their maximal atomic utilization, easily regulated active center and high catalytic activity, in which the coordination environment plays a crucial role in the intrinsic catalytic activity. Taking NiN as an example, this study reveals that the introduction of different numbers of S atoms into N coordination (Ni-NS ( = 1-4)) results in outstanding structural stability and catalytic activity. Owing to the additional orbitals around -1.60 eV and abundant Ni d, d, d, and d orbital occupation after S substitution, N,S coordination can effectively facilitate the protonation of adsorbed intermediates and thus accelerate the overall CORR. The CORR mechanisms for CO and HCOOH generation two-electron pathways are systematically elucidated on NiN, NiNS and NiNS. NiNS yields HCOOH as the most favorable product with a limiting potential of -0.24 V, surpassing NiN (-1.14 V) and NiNS (-0.50 V), which indicates that the different S-atom substitution of NiN has considerable influence on the CORR performance. This work highlights NiNS as a high-performance CORR catalyst to produce HCOOH, and demonstrates that N,S coordination is an effective strategy to regulate the performance of atomically dispersed electrocatalysts.