Facile in situ coupling CoFe/Co nanoparticles and N-doped carbon nanotubes/graphitic nanosheets as bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries

Abstract Exploring efficient and low-cost bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a critical challenge. Herein, a novel bifunctional electrocatalyst with CoFe/Co nanoparticles encapsulated in N-doped carbon nanotubes/graphitic nanosheets (CoFe/Co@NCNT/NG) is prepared by a facile pyrolysis strategy. The in situ generated CoFe alloy itself, as well as its synergistic interplay with metallic Co and NCNT/NG, shows good electron and charge transfer capability, and the hybrids afford abundant active sites on the surface, stimulating greatly excellent intrinsic bifunctional catalytic features with a small ORR/OER potential difference of 0.735 V. Furthermore, CoFe/Co@NCNT/NG as the air electrode catalyst can endow rechargeable Zn-air battery (ZAB) with superior performance of exceptional open-circuit voltage of 1.40 V, high peak power density of 161 mW cm−2. More importantly, CoFe/Co@NCNT/NG-based ZAB shows low charge-discharge voltage gap (0.819 V at 20 mA cm−2) and outstanding long-term galvanostatic charge-discharge cycle stability over 300 cycles at 2 mA cm−2 with each cycle of 20 min, which outperforms the benchmark Pt/C + RuO2-based ZAB. Particularly, a CoFe/Co@NCNT/NG-based flexible rechargeable solid-state ZAB also displays reliable compatibility toward bending conditions.