First-principles design of bifunctional oxygen reduction and evolution catalysts through bimetallic centers in metal-organic frameworks

Rational design of efficient bifunctional oxygen electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with low cost and high activity is greatly desired for the realization of rechargeable metal-air batteries and regenerative fuel cells. Metal-organic frameworks (MOFs) are promising oxygen electrocatalysts due to their flexible structures, ultrahigh surface area, porosity, and high catalytic activity. However, it is still a significant challenge to achieve bifunctional oxygen electrocatalysts based on MOF materials with comparable activity and durability. Herein, the electronic and catalytic properties of M-3(triphenylene-2,3,6,7,10,11-hexathiol)(2) [M-3(THT)(2)] nanosheets with nine different central metal atoms (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt) are investigated systematically based on density functional theory. It is found that the electronic and catalytic properties of M-3(THT)(2) nanosheets are mainly based on the central metal atoms. Of the nine different M-3(THT)(2) nanosheets considered, Co-3(THT)(2) displays the best ORR catalytic activity, while Fe-3(THT)(2) shows the best OER catalytic activity. Due to the separation by THT molecules, the electronic and catalytic properties of MS4 groups in bi-metallic M-3(THT)(2) nanosheets are consistent with their single-metal counterparts. Bi-metallic FexCo3-x(THT)(2) nanosheets exhibit bifunctional catalytic activity for both the ORR and OER. The ORR occurs on the Co atom, while the active site for the OER is the Fe atom. With desirable architecture and excellent electrocatalytic activities, the FexCo3-x(THT)(2) nanosheets can be considered as promising bifunctional oxygen electrocatalysts.