Inverse Spinel Cobalt-Iron Oxide and N-Doped Graphene Composite as an Efficient and Durable Bifuctional Catalyst for Li-O-2 Batteries

Rational design of efficient bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts are critical for rechargeable Li-O-2 batteries. Here, we report inverse spinel Co[Co,Fe]O-4/nitrogen-doped graphene (NG) composite used as a promising catalyst for rechargeable Li-O-2 batteries. The cells with Co[Co,Fe]O-4/NG catalyst exhibit high initial capacity, remarkable cyclability, and good rate capability. Moreover, the overpotential of the Li-O-2 batteries is reduced significantly. The improved ORR/OER performances are attributed to the good property of Co[Co,Fe]O-4 with an inverse spinel structure toward ORR and the improved electronic conductivity of N-doped graphene. The density functional theory (DFT) calculation shows the rate limitation step for ORR on the inverse spinel surface is the growth of the Li2O2 cluster while the rate limitation step for the OER pathway is the oxidation of Li2O2. The inverse spinel surface in Co[Co,Fe]O-4/NG is more active than that of the normal spinel phases for the Li-O-2 battery reactions. This work not only provides a promising bifunctional catalyst for practical metal air batteries but also offers a general strategy to rationally design catalysts for various applications.