Interconnected core-shell carbon nanotube-graphene nanoribbon scaffolds for anchoring cobalt oxides as bifunctional electrocatalysts for oxygen evolution and reductionElectronic supplementary information (ESI) available. See DOI: 10.1039/c5ta02967h

Bifunctional electrocatalysts for oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) are crucial to the development of regenerative fuel cells or rechargeable metal-air batteries. However, the sluggish kinetics of OER and ORR often require the use of precious metal-based catalysts such as iridium, ruthenium, and platinum to lower the energy barriers of OER and ORR. Developing a highly efficient and stable bifunctional catalyst that is made of non-precious elements for ORR and OER still remains a significant challenge. Here, we show a novel catalyst architecture based on coupling non-precious Co 3 O 4 nanocrystals onto nitrogen-doped, core-shell structured carbon nanotube-graphene nanoribbon (N-csCNT-GNR) scaffolds prepared by microwave-assisted, controlled upzipping of multiwall carbon nanotubes. The unzipped graphene nanoribbon shell enables a high surface area for loading of Co 3 O 4 nanocrystals while the intact inner carbon nanotube core facilitates efficient transport of electrons. The as-prepared Co 3 O 4 /N-csCNT-GNR composite catalysts exhibit remarkably high activity towards both OER and ORR as a result of synergistic interactions between Co 3 O 4 and the N-csCNT-GNR substrates. N-doped, core-shell carbon nanotube-graphene nanoribbons are developed as novel substrates for anchoring Co 3 O 4 nanocrystals as bifunctional catalysts for oxygen electrochemistry.