Porous MnNi₂O₄ nanorods as an efficient bifunctional catalyst for rechargeable Li-O₂ battery

Spinel-type porous MnNi₂O₄ nanorods are prepared using a facile electrospinning and subsequent calcination approach. A MnNi₂O₄ nanoparticle material is also synthesized via the sol-gel method to explore the effect of surface area, pore diameter and pore volume on catalytic activity. The crystal phase and morphology of the samples are confirmed by X-ray diffractometry and transmission electron microscopy. Linear sweep voltammetry analysis shows that the MnNi₂O₄ nanorods electrode exhibits better activities in oxygen reduction and evolution reactions than the prepared MnNi₂O₄ nanoparticles or Ketjenblack electrodes. The sequenced activities of these three materials are further supported by a reduction in both the discharge and recharge overpotentials during battery tests. Furthermore, batteries with the MnNi2O4 nanorods present improved rate capability and cyclability compared with the MnNi₂O₄ nanoparticles and Ketjenblack. This enhanced performance is explained by the large surface area, mean pore diameter, and pore volume of the MnNi₂O₄ nanorods. These results highlight the importance of porous MnNi₂O₄ nanorods as a prospective bifunctional catalyst and a potential method of electrospinning to scale up the preparation of catalysts for rechargeable Li-O₂ batteries.