Bimetallic Metal-Organic Frameworks as Efficient Cathode Catalysts for Li-O2 Batteries.

Metal-organic frameworks (MOFs) have the potential to improve the electrochemical performance of Li-O2 batteries with high O2 accessibility and catalytic activity of the open metal sites. Here, we explored bimetallic MnCo-MOF-74 as a cathode catalyst in Li-O2 batteries. MnCo-MOF-74 was synthesized with the Mn to Co ratio of 1:4 by a simple hydrothermal reaction. Compared to monometallic Mn-MOF-74 and Co-MOF-74 with only single catalytic activity for LiOH formation or oxygen evolution reactions, bimetallic MnCo-MOF-74 demonstrated a capability to facilitate improved reversibility and efficiency during both discharge and charge cycles. Benefitting from the porous structure of the MOF as well as the complementary contribution from both Mn- and Co-metal clusters, MnCo-MOF-74 outperformed Mn-MOF-74 and Co-MOF-74. A high full discharge capacity of 11 150 mAh g-1 at 200 mA g-1 was achieved in MnCo-MOF-74. During the cycling test, MnCo-MOF-74 stably delivered a limited discharge capacity of 1000 mAh g-1 for 44 cycles at 200 mA g-1, which is remarkably longer than those of carbon black, Mn-MOF-74, and Co-MOF-74 with cycle lives of 8, 22, and 18 cycles, respectively.