LAUSR

Abstract MgO-Co/N-doped carbon (NC) as highly efficient bifunctional electrocatalyst toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was developed by a facile two-step pyrolysis method. The resulting electrocatalysts have a hybrid nanostructure of MgO-Co hybrid nanoparticles coated with NC shells. Although MgO itself is inactive for both OER and ORR, it still plays important roles in enhancing OER and ORR activity of MgO-Co/NC electrocatalysts. Of importance, a moderate content of MgO is highly required. Specifically speaking, MgO with moderate content is favorable for the resulting MgO-Co/NC electrocatalysts to achieve high ratios of O vacancy/total O (~0.46), graphitic-N/total N (~0.30) and Co3+/Co0 (~10.33), thus benefitting OER activity. Moreover, a moderate content of MgO also facilitates the formation of the abundant active Co2+ species and a high Co2+/Co0 ratio (~9.56) is obtained in the resulting MgO-Co/NC, which is in favor of ORR activity. The optimized electrocatalyst shows a low Ej=10 (~1.56 V) for OER and a high value of E1/2 (~0.85 V) for ORR. Its overall bifunctional activity of ΔE (ΔE = Ej=10 − E1/2) is as low as ~0.71 V. Its outstanding OER/ORR activity and bifunctional activity are comparable or even superior to precious metal electrocatalysts and recently reported Co-based bifunctional electrocatalysts.