Integrating MXene nanosheets with cobalt-tipped carbon nanotubes for an efficient oxygen reduction reaction

The oxygen reduction reaction (ORR) plays a key role in many renewable energy conversion and storage technologies. As the state-of-the-art ORR electrocatalysts, Pt-based electrocatalysts suffer from high price, low earth abundance and poor stability. Developing high performance noble-metal-free ORR electrocatalysts as alternatives for Pt is highly desirable but still remains a significant challenge. In this work, we reported a metal-organic-framework- engaged strategy for the fabrication of cobalt-tipped carbon nanotube/Ti3C2 nanosheet composites (Co-CNT/Ti3C2), in which ZIF-67 particles were in situ grown on Ti3C2 nanosheets and then were converted to cobalt-tipped carbon nanotubes through a pyrolysis process. The Ti3C2 nanosheets not only served as two-dimensional conductive scaffolds for the growth of Co-CNTs but also balanced the tradeoff between graphitization of carbon and the surface area. Benefiting from the abundant Co-N/C active sites, reasonably high graphitization of carbon and suitable surface areas, the optimized Co-CNT/Ti3C2 manifested comparable ORR activity (half-wave potential of 0.82 V and diffusion-limiting current density of 5.55 mA cm(-2)) but superior stability to commercial Pt/C (half-wave potential of 0.82 V and diffusion-limiting current density of 5.30 mA cm(-2)), providing great opportunity for its application in renewable conversion and storage technologies.