Synthesis of ultrahigh-metal-density single-atom catalysts via metal sulfide-mediated atomic trapping

Single-atom catalysts (SACs) exhibit exceptional intrinsic activity per metal site, but are often limited by low metal loading, which compromises the overall catalytic performance. Pyrolytic strategies commonly used for synthesizing SACs generally suffer from aggregation at high metal loadings. Here we report a universal synthesis approach for ultrahigh-density metal–nitrogen–carbon (UHDM–N–C) SACs via a metal-sulfide-mediated atomization process. We show that our approach is general for transition, rare-earth and noble metals, achieving 17 SACs with metal loadings >20 wt% (including a loading of 26.9 wt% for Cu, 31.2 wt% for Dy and 33.4 wt% for Pt) at 800 °C, as well as high-entropy quinary and vicenary SACs with ultrahigh metal contents. In situ X-ray diffraction and transmission electron microscopy alongside molecular simulations reveals a dynamic nanoparticle-to-single atom transformation process, including thermally driven decomposition of the metal sulfide and the trapping of liberated metal atoms to form thermodynamically stable M–N–C moieties. Our studies indicate that a high N-doping is crucial for achieving ultrahigh-loading metal atoms and a metal-sulfide-mediated process is essential for avoiding metal aggregation at high loadings. As a demonstration, the metal-loading-dependent activity in electrocatalytic oxygen evolution reaction is demonstrated on SACs with increasing Ni content. Increasing the metal loading of single-atom catalysts (SACs) typically results in aggregation, which can have a detrimental effect on catalytic performance. Now, a nitrogen-doping-assisted atomization approach is reported that transforms metal-sulfide nanoparticles into ultrahigh-density metal–nitrogen–carbon SACs.