Facile route to achieve bifunctional electrocatalysts for oxygen reduction and evolution reactions derived from CeO2 encapsulated by the zeolitic imidazolate framework-67

Abstract

Highly efficient bifunctional electrocatalysts for both the oxygen reduction reaction and oxygen evolution reaction are essential for the development of rechargeable metal–air batteries. Herein, we demonstrate a novel bifunctional electrocatalyst with CeO₂ and Co nanoparticles being embedded in N-doped carbon, which is achieved via pyrolyzing CeO₂@zeolitic imidazolate framework-67 particles. In 0.1 M KOH aqueous solution, CeO₂/Co@N-doped carbon shows an excellent electrocatalytic performance with an oxygen reduction reaction onset potential of 0.998 V vs. a reversible hydrogen electrode with an oxygen evolution reaction overpotential of 474 mV at 10 mA cm⁻². The liquid rechargeable Zn–air battery that is assembled by using CeO₂/Co@N-doped carbon as the air cathode shows excellent charge/discharge performance, with an open-circuit potential of 1.42 V and a maximum power density of 102.69 mW cm⁻². Furthermore, the rechargeable Zn–air battery exhibits stable cycling performance at a constant current density of 5 mA cm⁻² after 70 hours, with a charge/discharge gap of only 0.8 V and round-trip efficiency of ca. 59%. The remarkable bifunctional properties are considered to arise from the synergistic effect between the N-doped carbon and CeO₂ nanoparticles, where abundant Ce³⁺ and oxygen vacancies in CeO₂ are generated and more defect sites are available in N-doped carbon.