Designing bifunctional catalysts for oxygen reduction/evolution reactions for high efficiency and long lifetime.

Designing efficient and durable bifunctional oxygen catalyst to replace expensive Pt catalysts in oxygen reduction reaction and oxygen evolution reaction is crucial for various energy conversion devices, such as metal-air batteries and fuel cells. Although various nanocarbon/metal oxides have been developed, their catalytic efficiencies remain unsatisfactory; moreover, bi-functionality and the issue of long-term durability have remained elusive goals. Herein, we report the self-assembly of interconnected nickel-cobaltite nanocrystals on nitrogen-doped graphene via hydrothermal synthesis. The Co3+ sites, the key radicals for bifunctional oxygen reduction and evolution reactions. Well-dispersed nitrogen-doped graphene serve as a platform for anchoring the interconnected nickel-cobaltite nanocrystals and improve the conductivity to maintain a high saturation current in oxygen reduction and low overpotential in evolution reaction, similar to Pt/C. Lifetimes as long as 200 h for oxygen reduction and 300 h for oxygen evolution are demonstrated with negligible degradations. The present approach paves the way for the rational design of various Gr-metal oxide hybrids for numerous applications. Image 1 • Interconnected i -NiCo 2 O 4 grown on nitrogen-doped graphene via self-assembly strategy. • The interconnected nanostructure prevented the migration of nanoparticles. • The electrocatalytic activity was evaluated in oxygen reduction/evolution reactions. • The hybrid exhibited high catalytic activity and long term durability. [ABSTRACT FROM AUTHOR]