Carbon-nanotube wall nanoengineering strategy to stabilize FeNi nanoparticles and Fe single atoms for rechargeable Zn–air batteries†

The great interest in rechargeable Zn–air batteries (ZABs) stimulates extensive research on efficient and robust electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a novel ORR/OER bifunctional catalyst is developed using carbon-nanotube wall nanoengineering. In this design, FeNi nanoparticles are inserted into the wall via a carbothermic reaction to enhance the OER, while isolated Fe atoms in iron-phthalocyanine anchored on the wall via π–π coupling interaction are used to catalyze the ORR. Accordingly, the resulting electrocatalyst exhibits outstanding ORR and OER activities such as a small potential difference of 0.67 V. In situ Raman spectroscopy measurements verify the presence of reconstruction transformation from an alloy phase to a high-activity spinel phase during the OER process. When used in ZABs, high peak power densities of 208.5 mW cm⁻² under a liquid-state electrolyte and 150.1 mW cm⁻² in a solid-state electrolyte are demonstrated. Furthermore, outstanding battery durability is illustrated by a small and stable charge–discharge voltage gap of 0.78 V at 10 mA cm⁻² after 1400 cycles. This study offers a novel method to fabricate bifunctional ORR/OER electrocatalysts and possibly extends to multi-site catalysts.