N, S coordination in Co single atom catalyst promoting CO2RR towards HCOOH at negative potentials

Abstract

Co-based single-atom catalysts (Co-SACs) have attracted widespread attention in electrocatalytic CO₂ reduction reaction (CO₂RR). The coordination environment around Co active centers plays a crucial role in determining their intrinsic catalytic activity. This work systematically investigates the effect of introducing different numbers of S atoms into the Co-N₄ coordination environment (Co-N_xS_4-x, x = 1––4) on the CO₂RR performance at negative potentials. Among all structures, para-sulfur doped structure (p-CoN₂S₂) performs best with the limiting potentials for HCOOH generation of –0.19, 0, and 0 V at –0.23, –0.54, and –0.84 V, respectively. Compared to CoN₄, the substitution of S atoms in p-CoN₂S₂ results in the emergence of two electron distribution peaks at –0.46 and –0.02 eV, primarily contributed by the Co $d_{\text{yz}}$ and $d_{\text{xz}}$ orbitals. This significantly reduces the band gap of p-CoN₂S₂ to 0.36 eV, much lower than that of CoN₄ (1.82 eV), thereby enhancing the electrical conductivity. Additionally, p-CoN₂S₂ exhibits a higher occupation of the Co $d_{z^2}$ orbital, which is beneficial for the electron transfer from Co atom to CO₂, thus promoting CO₂RR. This work highlights p-CoN₂S₂ as an efficient catalyst for HCOOH production, and demonstrates that the N, S coordination is an effective strategy to modulate the CO₂RR performance at negative potentials.