Mn-doped cobalt oxide dodecahedron nanocages as an efficient bifunctional electrocatalyst for zinc–air batteries†

Abstract

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a vital role in the functioning of Zn–air batteries and similar energy storage systems. These reactions are kinetically sluggish, which limits the performance of rechargeable Zn–air batteries. An effective bifunctional electrocatalyst that can replace the current noble metal based expensive systems is the need of the hour. In this study, Mn-doped cobalt oxide was synthesized using a cobalt zeolitic imidazolate framework (Co-ZIF) as a template. Mn-doped Co-ZIFs with different Co : Mn ratios (0.5, 1, and 2) were prepared using a single-pot technique and converted into corresponding Mn-doped cobalt oxides via calcination. Structural features were studied using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Mn-Co₃O₄ displayed a high Brunauer–Emmett–Teller (BET) surface area of 69 m² g⁻¹ and a high pore volume. Among all the studied compositions, Mn-Co₃O₄-1 (Co : Mn = 1) exhibited the best performance, illustrating the crucial role of an optimum level of Mn doping. Mn-Co₃O₄-1 displayed a low ORR onset potential of 0.94 V and high mass transfer limited current density of 5.65 mA cm⁻². The catalyst exhibited a low overpotential of 330 mV at a current density of 10 mA cm⁻² for the OER. It also exhibited excellent ORR and OER stability and good bifunctionality, with a potential difference of 0.71 V. This study illustrates the excellent performance of Mn-doped cobalt oxides produced using ZIF templates in oxygen electrocatalysis.