Sulfur-doping tunes p-d orbital coupling over asymmetric Zn-Sn dual-atom for boosting CO₂ electroreduction to formate

The interaction of p-d orbitals at bimetallic sites plays a crucial role in determining the catalytic reactivity, which facilitates the modulation of charges and enhances the efficiency of CO₂ electroreduction process. Here, we show a ligand co-etching approach to create asymmetric Zn-Sn dual-atom sites (DASs) within metal-organic framework (MOF)-derived yolk-shell carbon frameworks (named Zn₁Sn₁/SNC). The DASs comprise one Sn center (p-block) partially doped with sulfur and one Zn center (d-block) with N coordination, facilitating the coupling of p-d orbitals between the Zn-Sn dimer. The N-Zn-Sn-S/N arrangement displays an asymmetric distribution of charges and atoms, leading to a stable adsorption configuration of HCOO* intermediates. In H-type cell, Zn₁Sn₁/SNC exhibits an impressive formate Faraday efficiency of 94.6% at -0.84 V. In flow cell, the asymmetric electronic architecture of Zn₁Sn₁/SNC facilitates high accessibility, leading to a high current density of -315.2 mA cm^-2 at -0.90 V. Theoretical calculations show the asymmetric sites in Zn₁Sn₁/SNC with ideal adsorption affinity lower the CO₂ reduction barrier, thus improve the overall efficiency of CO₂ reduction.