Bifunctional catalysts of modified doped small-sized ZIF and CNTs with entangled structures

For optimizing the lifetime and power of Zn-Air batteries (ZABs), we develop Fe, Co bimetallic doped zeolite imidazolate framework (M@CoFe-ZIF-8) from the perspective of catalytic reaction. After the pyrolysis treatment, the catalyst shows an entangled structure of 100 nm-sized ZIF-8 particles and carbon nanotubes (CNTs). The experimental result shows that the 100 nm-sized CoFe@MNC-CNTs (MNC: metal and nitrogen doped carbon) have better ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) catalytic activities compared with the 1 μm-sized CoFe@BMNC-CNTs structures with the assistance of melamine. On the one hand, it is closely related to the larger specific surface area and mesoporous structure of CoFe@MNC-CNTs. On the other hand, uniformly distributed metal nitrogen (M-Nx) sites and carbon nanotube-wrapped metal nanoparticles may both be effective catalytic active sites for ORR and OER. The CoFe@MNC-CNTs exhibits remarkable catalytic performance, outperforming the commercially available 20 % Pt/C catalyst with a higher half-wave potential (0.865 V vs 0.838 V) in alkaline electrolyte. Meanwhile, the overpotential (Eover) also rivals that of the commercially available RuO2 catalyst. The Zn-air batterry based on CoFe@MNC-CNTs exhibits excellent power density, which is significantly better than Pt/C catalyst (112.1 mW·cm−2 vs 98.2 mW·cm−2). The CoFe@MNC-CNTs also exhibits over 65 h of cycling stability (10 mA·cm−2). In addition, the open circuit voltage (OCV) and cycle time of the flexible battery based on the catalyst of CoFe@MNC-CNTs remain satisfactory (1.525 V, 18 h).