Q. Niu, B. Chen, J. Guo, J. Nie, X. Guo, and G. Ma, “Flexible, Porous, and Metal–Heteroatom-Doped Carbon Nanofibers as Efficient ORR Electrocatalysts for Zn–Air Battery”, Nano-Micro Lett, vol. 11, p. 8, Jan. 2019.