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

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-N-4 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 halfwave potential of 0.89 V for ORR, outperforming that of most recent reported bifunctional electrocatalysts. Our Co-CoO@NSC catalyst indicates the Delta E (Delta E = E-j =10 (OER) E-1/2 (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.