Co₃O₄@Co/NCNT nanostructure derived from a dicyanamide-based metal-organic framework as an efficient bi-functional electrocatalyst for oxygen reduction and evolution reactions

Abstract

There has been growing interest in the synthesis of efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reactions (OER), for their potential use in a variety of renewable energy technologies, such as regenerative fuel cells and metal-air batteries. Here, a bi-functional electrocatalyst, derived from a novel dicyanamide based nitrogen rich MOF {[Co(bpe)₂(N(CN)₂)]⋅(N(CN)₂)⋅(5 H₂O)}_n [Co-MOF-1, bpe=1,2-bis(4-pyridyl)ethane, N(CN)2⁻=dicyanamide] under different pyrolysis conditions is reported. Pyrolysis of the Co-MOF-1 under Ar atmosphere (at 800 °C) yielded a Co nanoparticle-embedded N-doped carbon nanotube matrix (Co/NCNT-Ar) while pyrolysis under a reductive H₂/Ar atmosphere (at 800 °C) and further mild calcination yielded Co₃O₄@Co core–shell nanoparticle-encapsulated N-doped carbon nanotubes (Co₃O₄@Co/NCNT). Both catalysts show bi-functional activity towards ORR and OER, however, the core–shell Co₃O₄@Co/NCNT nanostructure exhibited superior electrocatalytic activity for both the ORR with a potential of 0.88 V at a current density of −1 mA cm⁻² and the OER with a potential of 1.61 V at 10 mA cm⁻² , which is competitive with the most active bi-functional catalysts reported previously.