Intrinsic mechanism-guided constant-potential density functional theory screening of two-dimensional conjugated metal-organic frameworks for CO₂ electroreduction

The development of efficient electrocatalysts for the CO₂ reduction reaction (CO₂RR) is essential for producing value-added targeted products. Two-dimensional conjugated metal-organic frameworks (2D c-MOFs), known for their high electrical conductivity, show great potential as efficient CO₂RR catalysts. However, the complex surface electrochemistry of these materials introduces intricate regulatory mechanisms governing their catalytic activity, posing challenges for establishing clear design principles. Herein, we systematically screen a series of transition metal-based 2D c-MOFs constructed from a 2,3,8,9,14,15-hexahydroxytribenzocyclyne (HHTC) linker for the electrocatalytic CO₂RR by using grand canonical density functional theory (GC-DFT) calculations. Among the 24 catalysts, 20 preferentially promote CO₂ reduction over hydrogen evolution, successfully suppressing the competing reaction while exhibiting high thermodynamic and electrochemical stability. By applying a stringent hydrogenation free-energy threshold of ΔG < 0.5 eV for the first three hydrogenation steps of CO₂, 15 promising catalysts were identified. Further mechanistic analysis based on free-energy barriers and selectivity evaluation narrowed the selection to 10 active catalysts. Ultimately, Ir₃(HHTC)₂ was identified as the most promising candidate, with the potential-determining step (PDS) being the hydrogenation of *CH₂OH to *CH₂, yielding CH₄ as the product and featuring a free-energy barrier of 0.08 eV. In contrast, Co₃(HHTC)₂ and Rh₃(HHTC)₂ exhibit higher activity and favor CH₃OH synthesis, with corresponding PDS barriers of 0.19 eV and 0.23 eV, respectively. Furthermore, Mn-, Fe-, Ni-, and Cu-based TM₃(HHTC)₂ primarily promote HCOOH production, with corresponding PDS barriers of 0.40 eV, 0.34 eV, 0.31 eV, and 0.29 eV, respectively. Our findings provide a rational framework to guide the design of high-performance and selective CO₂RR electrocatalysts.