Hierarchical CoS_x/graphene/carbon nanotube hybrid architectures for bifunctional electrocatalysts in zinc-air battery

Herein, we report multidimensional hybrid architectures wherein CoS₂ 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 CoS₂, 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 IrO₂ 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.