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