Multidimensional bimetallic-codoped MOF-derived M@N-CNTs bifunctional electrocatalysts for rechargeable zinc-air batteries

The design and synthesis of low-cost and efficient non-noble metal bifunctional electrocatalysts for enhancing the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a pressing demand for the development of rechargeable zinc-air batteries. In this paper, a range of metal@nitrogen-doped carbon nanotubes (M@N-CNTs, M = Fe, Ni) materials were prepared by the typical solvothermal synthesis with Fe and Ni co-doped zeolitic imidazolate framework-8 (ZIF-8) as precursors. The synthesized catalysts have a multidimensional structure of one-dimensional M-N-doped carbon nanotubes coexisting with carbonized M-N-doped dodecahedra, providing abundant catalytically active sites for oxygen, as well as multidimensional channels for mass diffusion and electron transport, thus exhibiting excellent catalytic activity and stability. The FeNi@N-CNTs-10 electrocatalyst possesses a half-wave potential of E1/2 = 0.92 V for ORR and Ej=10 = 1.46 V (η = 230 mV) for OER in 0.1 mol·L−1 KOH, which is superior to commercial 20 wt% Pt/C+ RuO2 (E1/2 = 0.82 V, Ej=10 = 1.61 V (η = 380 mV)). Zinc-air battery loaded with FeNi@N-CNTs-10 presents a power density of 187 mW·cm−2 and smaller voltage gap (1.0 V) than commercial Pt/C + RuO2 for >1600 discharge-charge cycles at 10 mA·cm−2. The outstanding performance is due to the multidimensional structure, high graphitization carbon and complementary effect between FeNi and M-Nx moiety. The design of multidimensional structure with bifunctional active sites could be extended to other metal-air batteries.