Hierarchical CoSx/graphene/carbon nanotube hybrid architectures for bifunctional electrocatalysts in Zinc-air battery

• Multidimensional CoS x @srGO/CNT hybrid architectures were synthesized. • CoS 2 nanoparticles catalyze the growth of CNT branches acting as active phase. • CoS x @srGO/CNT showed bifunctional ORR and OER activities. • The resulting Zn-air battery achieved high capacity and cyclic stability. Herein, we report multidimensional hybrid architectures wherein CoS 2 nanoparticles are encapsulated in steam-activated reduced graphene oxide/carbon nanotubes (CoS x @srGO/CNT) for rechargeable Zn-air batteries. CoS x nanoparticles work as catalysts to grow CNT branches onto the srGO, and the CoS x @srGO/CNT act as bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The bifunctional ORR and OER activities of the CoS x @srGO/CNT are substantially greater than those of CoS 2 , srGO, and CoS x @srGO as confirmed by onset potentials, Tafel and K-L plots, and mass activities. Zn-air batteries with CoS x @srGO/CNT catalyst achieved a specific capacity of 583 mAh·g zn − 1 and maximum power density of 66.45 mW·cm −2 , which are greater than Pt/C and IrO 2 mixed catalyst, along with a long-term cyclability of over 100 cycles. The outstanding performance of CoS x @srGO/CNT is attributed to the abundant exposed active sites of CoS x on a unique 3D multidimensional graphene/CNT hybrid architecture and the rapid mass/charge transport for the enhanced bifunctional activities.