Developing nitrogen and Co/Fe/Ni multi-doped carbon nanotubes as high-performance bifunctional catalyst for rechargeable zinc-air battery.

Rational construction of advanced bifunctional catalysts with dual-active-sites is still challenging for both oxygen reduction (ORR) and oxygen evolution reactions (OER). Herein, metal-doped dicyandiamide formaldehyde resin is innovatively exploited to synthesize N/Co/Fe/Ni multi-doped carbon nanotubes (denoted as CoFeNi@CNT) with metal-nitrogen-carbon (MNC) and CoFeNi nanoparticles as the ORR and OER active sites, respectively. Abundant active sites and high degree of graphitization enable CoFeNi@CNT with a high ORR half-wave potential of 0.82 V and a low OER overpotential of 440 mV at 10 mA cm, which are comparable or superior to noble-metal catalysts. Particularly, the CoFeNi@CNT air electrode of rechargeable Zn-air batteries shows remarkable open circuit potential (1.46 V), discharge power density (152.3 mW cm), specific capacity (814 mAh g), and cycling stability for more than 250 h. It is worth emphasizing that this synthesis strategy is rather simple, low-cost, high yield, and the proportion and amount of doped metal ions can be easily adjusted according to the needs for different applications.