Designing N-doped carbon nanotubes and Fe-Fe3C nanostructures co-embedded in B-doped mesoporous carbon as an enduring cathode electrocatalyst for metal-air batteries

Oxygen reduction and evolution reactions are of immense importance in electrochemical conversion/ storage devices like regenerative/alcohol/hydrogen based fuel cells and metal-air batteries. Here, a rational facile synthesis methodology has been developed to design N-doped carbon nanotubes (N-CNTs) and Fe-Fe3C nanostructures co-embedded in B-doped mesoporous carbon nanostructures (BFNCNTs) as a noble metal-free superior bi-functional electrocatalyst for oxygen evolution/reduction reactions. The incorporation of N and B with negligible/undetectable B-N formation and Fe-Fe3C nanostructures leads to the superior performance by introducing plenty of defects, local heterogeneity and a high specific surface area (similar to 272 m(2) g(-1)). Besides, mesoporous boron-doped carbon acts as a host material for NCNTs and Fe-Fe3C, and it offers good connectivity as well as a protective coating for durable catalysis. Remarkably, more positive onset (-30 mV) and half-wave potentials (-225 mV) with -94% current retention under accelerated stability test and fuel tolerance for the ORR, in combination with lower onset (422 mV) and E-j=10(OER) (562 mV) potentials with high current density (190 mA cm(-2) @ 0.8 V vs. Ag/AgCl) for the OER as compared to commercial state-of-the-art electrocatalysts suggest superior bifunctional behavior of BFNCNTs. The complete oxygen electrochemical activity Delta E = E-j(OER)=10 = E-1/2(ORR) = 0.788 V for BFNCNTs is lower than recently reported various state-of-the-art bifunctional catalysts. Besides, a prototype battery fabrication using BFNCNTs as the cathode electrode for driving a light emitting diode has been demonstrated. Overall, BFNCNTs have potential to serve as a non-precious electrocatalyst for electrochemical energy devices.