Thiourea-Zeolitic imidazolate Framework-67 assembly derived Co–CoO nanoparticles encapsulated in N, S Codoped open carbon shell as bifunctional oxygen electrocatalyst for rechargeable flexible solid Zn–Air batteries

Abstract

A high active and stable bifunctional oxygen electrocatalyst of Co–CoO multiphase nanoparticles (NPs) encapsulated in N,S co-doped carbon shells (Co–CoO@NSC) is designed and constructed by in-situ S doping of ZIF-67 with thiourea and subsequent pyrolysis, which not only generates small Co–CoO NPs due to the steric effect, but also creates more active sites and defects. First-principles simulations reveal that in-situ S-doping optimizes the charge distribution of Co–N4 sites and Co–O–C bonds, which reduces the formation energy of *OOH and then improves the ability of oxygen adsorption and hydrogen peroxide desorption. The optimized Co–CoO@NSC exhibits excellent catalytic activity with the overpotential of only 279 mV at 10 mA cm−2 for OER and the half-wave potential of 0.89 V for ORR, outperforming that of most recent reported bifunctional electrocatalysts. Our Co–CoO@NSC catalyst indicates the ΔE (ΔE = Ej=10 (OER) − E1/2 (ORR)) of 0.68 V, which is smaller than the Pt/C + RuO2 system. Flexible solid-state Zn-air battery with Co–CoO@NSC-5 as air-electrode possesses a high power density (87.7 mW cm−2) as well as good bending flexibility. The simple synthesis method proposed in our paper is beneficial for inspiring the development for high active and stable bifunctional non-noble metal electrocatalysts in next-generation flexible electronic devices.