Carbon tube-graphene heterostructure with different N-doping configurations induces an electrochemically active-active interface for efficient oxygen electrocatalysis

Abstract To accelerate the sluggish kinetics for oxygen reduction/evolution reaction (ORR/OER) of metal-free carbon catalysts, we here report an electrochemically active-active interface for promoting ORR/OER kinetics, which is constructed by in-situ coupling N-doped sub-micron carbon tubes (N-SMCTs, electron donors) with N-doped reduced graphene oxide (N-rGO, electron acceptors). We find that N-SMCTs@N-rGO yields superior bifunctional ORR/OER activity with high durability (E1/2 of 0.87 V for ORR, η10 of 351 mV for OER). Moreover, the zinc-air battery with this material as an electrode displays high power density of 126 mW cm−2 with excellent cycle stability. Density functional theory (DFT) unveils a dual-site mechanism: the carbon adjacent to graphitic-N in N-SMCTs is the most active site for *OOH intermediate while the carbon neighboring to pyridinic-N in N-rGO is beneficial for the adsorption of *O/*OH intermediates. The unique active-active interface with dual-site mechanism suggests its potential to overcome energy barrier bottleneck in the traditional bifunctional oxygen catalysts.