Dual-metal-organic frameworks as ultrahigh-performance bifunctional electrocatalysts for oxygen reduction and oxygen evolution

At present, it is significant to research bifunctional catalysts for metal-air batteries with bargain price, excellent stability, and satisfactory activity. Herein, by density functional theory, the performance of dual-metal-organic frameworks M2-BTC (M2 = Ni2, Fe2, Co2, FeNi, CoNi, FeCo) as bifunctional electrocatalysts to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is investigated. All M2-BTC are proved to possess satisfactory thermodynamical stability. For ORR, FeNi-Ni, Ni2-BTC, Co2-BTC, and CoNi-Ni are confirmed to have high activity with corresponding overpotential of 0.40, 0.25, 0.31, and 0.28 V, respectively, which are both better than Pt(111) (ηORR = 0.45 V). For OER, Fe2-BTC, Ni2-BTC, Co2-BTC, and CoNi-Ni show excellent catalytic activity, with the overpotential of 0.42, 0.38, 0.22, and 0.31 V, respectively, which can be compared to RuO2(110) (ηOER = 0.37 V) or even better than it. According to the ORR/OER potential gap, Ni2-BTC, Co2-BTC, and CoNi-Ni are screened out to be ultrahigh-performance bifunctional electrocatalysts. The results of the highest occupied molecular orbital and the lowest unoccupied molecular orbital confirm that the metal atom is the main active site, and the O atoms attached to the active metal also participate in the reaction. Density of states analysis indicates that the different catalytic performance of M2-BTC is caused by the variety of electronic structures.