Dual-sources directed construction of N-doped carbon nanotube arrays as superior Self-supported bifunctional air electrodes for Rechargeable/ Flexible Zinc-air batteries

Developing advanced hybrid nanocatalysts comprising non-precious metal alloys encased in nitrogen-doped carbon matrix are extremely promising to promote the oxygen electrochemistry, though the elaborate con-struction of highly-dispersed and stable metal-N-C active sites remains a tough challenge. Herein, we crafted self-supported CoFe nanoalloys catalyst confined in N-doped carbon nanotube arrays rooting on carbon cloth (CoFe@NCNTs) via a simple dual-sources directed synthetic route. Experimental results demonstrate that well -constructed CoFe@NCNTs catalyst owns attractive benefits including 3D interconnected conductive network, porous heterostructure and sufficient active sites, accelerating the mass transport and interfacial charge transfer to improve the redox kinetics for bifunctional oxygen catalysis. Theoretical calculation analyses further demonstrate the synergistic bimetallic effect in CoFe@NCNTs for effective adsorption of oxygen intermediates. Accordingly, CoFe@NCNTs achieves low overpotentials for OER and ORR. Also, aqueous rechargeable zinc-air batteries (ZABs) with the self-supported CoFe@NCNTs air cathode deliver high gravimetric energy density of 966.4 Wh kgZn-1 at 10 mA cm-2, a maximum power density of 158.4 mW cm-2 and superb cycling stability of over 400 h/1000 cycles. High performance all-solid-state flexible ZABs are also realized with high discharge capac-ities, impressive peak power density, superior rate capabilities and prominent mechanical flexibility toward various practical applications. This study could provide an alternative avenue to establish cost-effective non -precious metal nanoalloys-based multifunctional electrocatalysts.