Nitrogen-doped reduced-graphene oxide as an efficient metal-free electrocatalyst for oxygen reduction in fuel cells

Abstract

The electronic and chemical properties of reduced-graphene oxide (RGO) can be modulated by chemical doping of foreign atoms and functional moieties. In this work, a low-cost industrial material, 5-aminotetrazole monohydrate (AM) was chosen to modify RGO by a facile, catalyst-free thermal annealing approach in largescale. The obtained nitrogen-doped reduced-graphene oxide (N-RGO), as a metal-free catalyst for oxygen reduction, was characterized by XRD, XPS, Raman, SEM, TEM and electrochemical measurements. It was found that the optimum synthesis conditions were a mass ratio of graphene oxide (GO) and AM equal to 1 : 25 and an annealing temperature of 700 °C. Detailed X-ray photoelectron spectrum analysis of the optimum product shows that the atomic percentage of the N-RGO samples can be adjusted up to 10.6%. Electrochemical characterizations clearly demonstrate excellent electrocatalytic activity of N-RGO toward the oxygen reduction reaction (ORR) in alkaline electrolytes via a four-electron pathway. The total content of graphitic and pyridinic nitrogen atoms is the key factor to enhance the current density in the electrocatalytic activity for ORR. This simple, cost-effective and scalable approach opens up the possibility for the synthesis of other nitrogen doping materials in gram-scale. It can be applied to various carbon materials for the development of other metal-free efficient ORR catalysts for fuel cell applications and even new catalytic materials for applications beyond fuel cells.