TiC- and TiN-Supported Single-Atom Catalysts for Dramatic Improvements in CO₂ Electrochemical Reduction to CH₄

CO 2 electrochemical catalysis is limited by scaling relations due to a d-band theory of transition metals. As a means of breaking the scaling relation, it has recently been reported that hybridizing the d-orbitals of transition metal with p-orbitals of main group elements or using naturally hybridized materials such as metal carbides and nitrides is a promising strategy. In this Letter, by means of density functional theory calculations, we investigate the catalytic properties of TiC, TiN, and single-atom catalysts supported on them for CO 2 electrochemical reduction. In particular, we found that when single transition-metal atoms are inserted into the surface defect sites of TiC, denoted as M@d-TiC (M = Ag, Au, Co, Cu, Fe, Ir, Ni, Os, Pd, Pt, Rh, or Ru), the iridium-doped TiC (Ir@d-TiC) is found to have a remarkably low overpotential of −0.09 V, the lowest value among any catalysts reported in the literature to selectively produce CH 4 (−0.3 ∼ −1.0 V). It is also shown that possible surface protonation reactions on TiC as a side reaction can be ignored because the overpotential (−0.38 V) is significantly larger than that of the CO 2 electrochemical reduction reaction on single-atom catalysts (e.g., −0.09 V). The origin of an extraordinary catalytic activity of Ir@d-TiC is also explained. This work clearly demonstrates the great potential of carbides and single-atom catalysts supported on TiC as active and selective CO 2 reduction catalysts, and perhaps for other electrochemical applications as well.