Toward Full Exposure of "active Sites": Nanocarbon Electrocatalyst with Surface Enriched Nitrogen for Superior Oxygen Reduction and Evolution Reactivity

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a decisive role for the efficiency of fuel cells and metal-air batteries. The nitrogen doped carbon materials with low cost and long durability are potential catalysts to replace precious metal catalyst for oxygen electrochemistry; however, the unexposed active sites induced by the bulk dopant atoms are hardly accessible and consequently scarcely contribute to the catalytic property. In this study, carbon nanotubes (CNTs) are selected as the platform to demonstrate the potential of full exposure of 'active sites' at the surface. Novel N-doped carbon coaxial nanocables with the pristine CNTs as the core and the N-doped carbon layers as the shell are proposed. The accessible and efficient utilization of the integrated nitrogen atoms enriched on the surface, together with the undestroyed intact inner walls, render the electrocatalyst much enhanced electrocatalytic activity and high electrical conductivity of 3.3 S cm^-1, therefore, N-doped nanocables afford higher oxygen reduction current, ∼51 mV positively shift onset potential, low peroxide generation, as well as lower overpotential and higher current for oxygen evoluation reaction. Nitrogen-doped coaxial carbon nanocables with most of the active sites fully exposed on the surface are developed. The accessible and efficient utilization of the integrated N atoms enriched on the surface combined with the undestroyed intact inner walls afford the nanocarbon electrocatalysts with much enhanced electrocatalytic activity for both oxygen reduction and evolution reaction.