In-situ synthesis of encapsulated N-doped carbon metal oxide nanostructures for Zn-air battery applications

La, Mn and Co-based materials with diverse compositions encapsulated in N-doped carbon materials were synthesized by an in-situ sol-gel method. The as-prepared materials were physically activated with CO2 giving as a result composites with excellent performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The composites were characterized by different physicochemical techniques revealing the importance of porosity created by CO2 activation. This crucial step increases the number of accessible active sites such as Co-Nx-C sites, Co/MnO heterointerfaces and graphitic N groups. Moreover, the formation of La2O2CO3 was detected to enhance electrical conductivity and electrochemical performance and it is active for ORR. Although the composite containing La, Mn and Co has less concentration of the highly active sites, its small particle size favour a better distribution of these sites. The Co-containing composites were tested as air-electrodes in a Zn-air battery and compared to commercial electrocatalysts. All composites showed a better operation in terms of higher cyclability and higher energy density which is a consequence of metal nanostructures encapsulation in N-doped porous carbon shells. Interestingly, the pure Co-based composite showed an outstanding performance related to the high concentration of the Co-Nx-C active sites that provide high activity and stability.