Two-Dimensional Fe-Hexaaminobenzene Metal–Organic Frameworks as Promising CO₂ Catalysts with High Activity and Selectivity

Motivated by the recent synthesis of two-dimensional (2D) metal–organic frameworks TM₃(HAB)₂ (TM = Fe, Co, Ni, Cu; HAB = hexaaminobenzene) with good intrinsic conductivity, for the first time, we explore the CO₂ conversion performance of these 2D sheets using density functional theory combined with the computational hydrogen electrode model. We find Fe₃(HAB)₂ as a promising material for electrocatalytic CO₂ reduction reaction. Reaction energy calculations identify the preferred pathway for CO₂ conversion to CH₃OH on Fe₃(HAB)₂ via an “RWGS + CO-hydro” process in which the corresponding free energy change is 0.69 eV and the activation energy barrier is 1.36 eV. In addition, the formation of *CHO through the hydrogenation of *CO is the rate-limiting step with the highest thermodynamic and kinetic barrier in elementary reactions. Compared with Cu(211), which exhibits the highest catalytic activity among all transition metals, Fe₃(HAB)₂ has a better catalytic activity with a lower overpotential for CO₂ reduction and a better selectivity with a much higher overpotential for the side reaction.