Cobalt/Zinc Dual-sites Coordinated with Nitrogen in Nanofibers Enabling Efficient and Durable Oxygen Reduction Reaction in Acidic Fuel Cells
The key to reducing the cost of proton-exchange-membrane fuel cells (PEMFCs) is to develop highly efficient non-precious metal catalysts for the cathodic oxygen reduction reaction (ORR). Herein, we fabricated Co/Zn atomic dual-sites anchored on N doped carbon nanofibers (Co/Zn-NCNF) catalyst via electrospinning, carbonization and post-treatments technologies. Aberration-corrected scanning transmission electron microscope (AC-STEM) verifies the existence of uniformly dispersed Co/Zn atomic pair within the NCNF. Meanwhile, the X-ray adsorption fine structure spectroscopy (XAFS) combined with fitting and calculated results further ascertain the coordination structure of Co/Zn dual-sites with the configuration of N2CoN2ZnN2. Such a Co/Zn-NCNF catalyst exhibits greatly enhanced ORR activity with the onset (Eonset) and half-wave (E1/2) potentials of 0.997 and 0.797V/RHE in acidic electrolyte, compared to the Co or Zn mono-doped sample. Density functional theoretical (DFT) calculation reveals that the novel N2CoN2ZnN2 structure, different from the traditional Co-N4 or Zn-N4, could largely lower the dissociative barrier of *OOH intermediate during the ORR, thereupon boosting the electrocatalytic performance. Finally, the assembled H2-O2 PEMFC using Co/Zn-NCNF as cathodic catalyst displays a maximum power density of 0.603 W cm-2 together with a remarkable stability after 150 h discharging at current density of 400 mA cm-2, paving the way for the future development of non-precious metal PEMFCs.