Carbon cloth-based nitrogen-doped carbon nanotube-encapsulated Co nanoparticles as bifunctional oxygen electrocatalysts for flexible Zn-air batteries

• N-doped CNTs-encapsulated Co nanoparticles on carbon cloth as freestanding air electrode. • Co/NCNTs/CC-1 exhibits excellent bifunctional catalytic activity for OER/ORR. • The air electrode enables excellent performance for liquid and flexible ZABs. To enhance the performance of Zn-air batteries (ZABs), it is critical to reduce the energy barriers of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) at the air cathode while accelerating their reaction kinetics. In this study, a self-supported bifunctional oxygen catalyst was prepared by growing nitrogen-doped carbon nanotubes (NCNTs) encapsulating Co nanoparticles on carbon cloth (CC), denoted as Co/NCNTs/CC. Benefiting from abundant active sites and a self-supported structure, the optimized Co/NCNTs/CC-1 exhibits a half-wave potential of 0.86 V for ORR and an overpotential of 243 mV at a current density of 10 mA cm −2 for OER. Density functional theory (DFT) calculations combined with experimental results reveal that the combination of Co nanoparticles and NCNTs improves the adsorption-desorption ability of oxygenated intermediates, synergistically enhancing the bifunctional catalytic efficiency. ZABs constructed with Co/NCNTs/CC-1 exhibit an open-circuit voltage of 1.45 V and demonstrate superior stability compared to ZABs assembled with Pt/C+RuO 2 . Additionally, flexible ZABs exhibit good battery performance and bending charge-discharge capabilities. This research offers a promising strategy for the development of non-precious metal catalysts for ZABs. In this study, we present the rational design of nitrogen-doped carbon nanotube-encapsulated Co nanoparticles (Co/NCNTs/CC) on carbon cloth, which serve as self-supporting air electrodes for both liquid-state and flexible Zn-air batteries.