In-situ formation of hierarchical 1D-3D hybridized carbon nanostructure supported nonnoble transition metals for efficient electrocatalysis of oxygen reaction.

Graphical abstract Herein, we designed a strategy to successfully synthesize a novel bi-functional rambutan-like oxygen electrocatalysts comprising in situ -formed N-doped metal (metal: Fe, Co or Ni) encapsulated carbon nanotubes grown on hollow-mesoporous carbon sphere (denoted as Me@N-CNT/HMCS). Metal acetate can catalyze melamine to generate uniformly distributed N-CNTs nanotubes at the surface of hollow-mesoporous carbon sphere. The Me@N-CNT/HMCS oxygen electrocatalysts with very low metal content show unexpectedly high catalytic activities toward both ORR, which is superior to commercial Pt/C. Especially, the optimized performance of Fe@N-CNT/HMCS is achieved with more positive onset potential (E 0 = 1.012 V) and half-wave (E 1/2 = 0.833 V). Additionally, this result indicated that excellent performance is attributed to the synergistic effect involve chemical composition, good conductivity, high porosity and unique rambutan-like structure. Highlights • We firstly reported a simple strategy to successfully synthesize high-performance bi-functional electrocatalysts of the 1D-3D rambutan-like carbon materials. • The excellent electrocatalytic activity was assigned to the synergistic effect between N doping, metal loading and rambutan-like electrocatalyst morphology. • The theoretical calculation study suggests that metallic Fe cluster can promote the O 2 adsorption strength in such chemical environment. Abstract Electrocatalysis of oxygen reaction is a critical step in operation of fuel cells and metal-air batteries. For the practical applications, the inexpensive non-noble metals catalysts with highly activity and stable need to be explored and utilized. Herein, a strategy for the preparation of a bi-functional rambutan shaped oxygen electrocatalyst is presented. The novel electrocatalyst is formed in situ with N doped carbon nanotubes grown on metal encapsulated hollow-mesoporous carbon sphere (Me@N-CNT/HMCS). The Me@N-CNT/HMCS oxygen electrocatalysts show high catalytic activities towards ORR, comparable to commercial Pt/C catalyst. The optimized performance of Fe@N-CNT/HMCS was achieved with a positive onset potential of 1.012 V and half-wave potential of 0.833 V. It is emphasized that Me@N-CNT/HMCS shows high stability and enhanced tolerance against methanol in alkaline medium. The Fe@N-CNT/HMCS electrocatalyst possessed a high OER activity with a low overpotential of 0.35 V at 10 mA cm−2 current density. The excellent performance could be attributed to the synergistic effect involving chemical composition, high conductivity, good porosity and unique rambutan-like structure. In addition, the theoretical calculation study suggests that metallic Fe cluster can promote the O 2 adsorption strength in such chemical environment. [ABSTRACT FROM AUTHOR]