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 Fe-3(HAB)(2) as a promising material for electrocatalytic CO2 reduction reaction. Reaction energy calculations identify the preferred pathway for CO2 conversion to CH3OH on Fe-3(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, Fe-3(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.