How Doped MoS₂ Breaks Transition-Metal Scaling Relations for CO₂ Electrochemical Reduction

Linear scaling relationships between the adsorption energies of CO₂ reduction intermediates pose a fundamental limitation to the catalytic efficiency of transition-metal catalysts. Significant improvements in CO₂ reduction activity beyond transition metals require the stabilization of key intermediates, COOH∗ and CHO∗ or COH∗, independent of CO∗. Using density functional theory (DFT) calculations, we show that the doped sulfur edge of MoS₂ satisfies this requirement by binding CO∗ significantly weaker than COOH∗, CHO∗, and COH∗, relative to transition-metal surfaces. The structural basis for the scaling of doped sulfur edge of MoS₂ is due to CO∗ binding on the metallic site (doping metal) and COOH∗, CHO∗, and COH∗ on the covalent site (sulfur). Linear scaling relations still exist if all the intermediates bind to the same site, but the combined effect of the two binding sites results in an overall deviation from transition-metal scaling lines. This principle can be applied to other metal/p-block materials. We rationalize the weak binding of CO∗ on the sulfur site with distortion/interaction and charge density difference analyses.