Formation of mesoporous Co/CoS/Metal-N-C@S, N-codoped hairy carbon polyhedrons as an efficient trifunctional electrocatalyst for Zn-air batteries and water splitting.

• Co/CoS/Metal-N-C@S, N-codoped mesoporous carbon polyhedrons are synthesized. • The specific roles of Co, CoS and (Co, Fe)-N-C active species are well recognized. • An ORR onset potential of 0.971 V and a half-wave potential of 0.906 V are achieved. • The assembled rechargeable Zn-air battery exhibits a high-power density of 213 mW cm−2. It remains a huge challenge to design and realize trifunctional high-efficiency and low-cost electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, with the introduction of CdS and ferrocene, a metal–organic framework (MOF)-induced strategy is reported to synthesize a hierarchical trifunctional electrocatalyst based on Co/CoS nanoparticles and metal (Co, Fe)-N-C species in a hairy S, N-codoped mesoporous carbon polyhedron interwoven with carbon nanotubes (Co/CoS/Fe-HSNC). The specific roles of Co, CoS and (Co, Fe)-N-C active species in Co/CoS/Fe-HSNC catalyst for ORR, OER and HER are also well recognized. Besides, CdS nanoparticles is demonstrated to act as a pore former and S sources both for reaction and doping, and ferrocene is employed to initiate the in-situ growth of carbon nanotubes and Fe-N-C active sites which both contribute to superior multifunctional activities. Benefitting from the rationally designed nanostructures, the ORR half-potential of the Co/CoS/Fe-HSNC electrocatalyst reaches 0.906 V in 0.1 M KOH, about 65 mV larger than commercial Pt/C electrocatalyst, and a low overpotential of 250 mV is achieved for OER and 138 mV for HER at a current density of 10 mA cm−2. Constructed with the Co/CoS/Fe-HSNC catalyst, a Zn-air battery exhibits a high power density of 213 mW cm−2 and a small charge/discharge voltage gap of 0.79 V at 2.0 mA cm−2. The presented strategy provides new insight into the construction of MOF-derived hierarchical multifunctional catalysts for Zn-air batteries and water electrolysis. [ABSTRACT FROM AUTHOR]