Bimetal zeolitic imidazolate framework (ZIF-9) derived nitrogen-doped porous carbon as efficient oxygen electrocatalysts for rechargeable Zn-air batteries

Abstract The commercialization of oxygen-related energy storage/conversion devices, for instance metal-air batteries or fuel cells, is highly dependent on development of low-cost, high performance electrocatalysts for oxygen reduction/oxygen evolution reactions (ORR and OER). In the present study, we employed Co-ZIF-9 as a sacrificial precursor to synthesize highly efficient bifunctional ORR/OER electrocatalysts through tuning the pyrolysis temperature and Fe-doping of the zeolitic imidazolate framework. The synthesized samples were characterized extensively using X-ray photoelectron spectroscopy (XPS), X-ray diffraction, elemental CHN and ICP analyses, and Fourier transform infrared (FTIR) spectroscopy as well as scanning (SEM) and transmission (TEM) electron microscopies. It has been found that the Fe-doping can significantly affect the electrocatalytic activity of the product through improving the number of transferred electrons. The ZIF-9_Fe3_Pyrol exhibited excellent electrocatalytic activity towards ORR (E onset  = 0.90 V vs. RHE) and OER (E onset  = 1.55 V vs. RHE), much better than other evaluated catalysts and comparable to the commercial PtRuC bifunctional catalyst. Moreover, the ZIF-9_Fe3_Pyrol sample outperformed the precious PtRuC catalyst with very little decay in ORR and OER activity over long continuous operation. The ZIF-9_Fe3_Pyrol exhibited excellent performance as a cathode catalyst in rechargeable Zn-air batteries, superior to the one assembled with the state-of-the-art catalyst.