MnF 2 Surface Modulated Hollow Carbon Nanorods on Porous Carbon Nanofibers as Efficient Bi-Functional Oxygen Catalysis for Rechargeable Zinc-Air Batteries.

Developing highly efficient bi-functional noble-metal-free oxygen electrocatalysts with low-cost and scalable synthesis approach is challenging for zinc-air batteries (ZABs). Due to the flexible valence state of manganese, MnF 2 is expected to provide efficient OER. However, its insulating properties may inhibit its OER process to a certain degree. Herein, during the process of converting the manganese source in the precursor of porous carbon nanofibers (PCNFs) to manganese fluoride, the manganese source is changed to manganese acetate, which allows PCNFs to grow a large number of hollow carbon nanorods (HCNRs). Meanwhile, manganese fluoride will transform from the aggregation state into uniformly dispersed MnF 2 nanodots, thereby achieving highly efficient OER catalytic activity. Furthermore, the intrinsic ORR catalytic activity of the HCNRs/MnF 2 @PCNFs can be enhanced due to the charge modulation effect of MnF 2 nanodots inside HCNR. In addition, the HCNRs stretched toward the liquid electrolyte can increase the capture capacity of dissolved oxygen and protect the inner MnF 2 , thereby enhancing the stability of HCNRs/MnF 2 @PCNFs for the oxygen electrocatalytic process. MnF 2 surface-modulated HCNRs can strongly enhance ORR activity, and the uniformly dispersed MnF 2 can also provide higher OER activity. Thus, the prepared HCNRs/MnF 2 @PCNFs obtain efficient bifunctional oxygen catalytic ability and high-performance rechargeable ZABs.