Single-atom catalysts confined in shell layer achieved by a modified top-down strategy for efficient CO reduction.

High-temperature pyrolysis is a primary method for synthesizing single-atom catalysts (SACs). However, this method accelerates the migration of metal atoms within the solid support, leading to low atom utilization. Herein, we report a novel top-down synthesis strategy wherein surface-sintered nickel sulfide (NiS) nanoparticles (NPs) are in situ atomized into single atoms, achieving confinement of the single-atom catalyst within the shell layer and synthesizing a high-performance single-atom catalyst. Systematic investigations indicate that driven by strong interactions between metal atoms and the support, the NiS NPs on the surface of the support atomize into single Ni atoms, which are predominantly distributed on the support surface, thus enhancing the accessibility of the active sites. Furthermore, theoretical calculations indicate that introducing S atoms into the second coordination shell around Ni atoms significantly reduces the activation energy of the CO reduction reaction, thereby enhancing the catalytic performance of the single-atom catalyst. In the flow cell, the Ni single-atom catalyst achieving nearly 100% Faradaic efficiency for CO (FE) over a wide potential range of -0.5 to -1.3 V versus reversible hydrogen electrode (vs. RHE). At -1.6 V vs. RHE, the partial current density for CO reaches a maximum of 709 mA cm (turnover frequency of 28.67 s) with a FE of 95.9%.