Simultaneously Integrating Single Atomic Cobalt Sites and Co9S8 Nanoparticles into Hollow Carbon Nanotubes as Trifunctional Electrocatalysts for Zn-Air Batteries to Drive Water Splitting

The development of rechargeable metal-air batteries and water electrolyzers are highly constrained by electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). However, the construction of efficient trifunctional electrocatalysts for ORR/OER/HER are highly desirable yet challenging. Herein, hollow carbon nanotubes integrated single cobalt atoms with Co9S8 nanoparticles (CoSA + Co9S8/HCNT) are fabricated by a straightforward in situ self-sacrificing strategy. The structure of the CoSA + Co9S8/HCNT are verified by X-ray absorption spectroscopy and aberration-corrected scanning transmission electron microscopy. Theoretical calculations and experimental results embrace the synergistic effects between Co9S8 nanoparticles and single cobalt atoms through optimizing the electronic configuration of the CoN4 active sites to lower the reaction barrier and facilitating the ORR, OER, and HER simultaneously. Consequently, rechargeable liquid and all-solid-state flexible Zn-air batteries based on CoSA + Co9S8/HCNT exhibit remarkable stability and excellent power density of 177.33 and 51.85 mW cm(-2), respectively, better than Pt/C + RuO2 counterparts. Moreover, the as-fabricated Zn-air batteries can drive an overall water splitting device assembled with CoSA + Co9S8/HCNT and achieve a current density of 10 mA cm(-2) at a low voltage of 1.59 V, also superior to Pt/C + RuO2. Therefore, this work presents a promising approach to an efficient trifunctional electrocatalyst toward practical applications.