Nitrogen-Doped Graphene: The Influence of Doping Level on the Charge-Transfer Resistance and Apparent Heterogeneous Electron Transfer Rate.

Maria Coros,Florina Pogacean,Stela M Pruneanu,Codruta Varodi,Emese Gal

doi:10.3390/s20071815

Abstract

Three nitrogen-doped graphene samples were synthesized by the hydrothermal method using urea as doping/reducing agent for graphene oxide (GO), previously dispersed in water. The mixture was poured into an autoclave and placed in the oven at 160 °C for 3, 8 and 12 h. The samples were correspondingly denoted NGr-1, NGr-2 and NGr-3. The effect of the reaction time on the morphology, structure and electrochemical properties of the resulting materials was thoroughly investigated using scanning electron microscopy (SEM) Raman spectroscopy, X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), elemental analysis, Cyclic Voltammetry (CV) and electrochemical impedance spectroscopy (EIS). For NGr-1 and NGr-2, the nitrogen concentration obtained from elemental analysis was around 6.36 wt%. In the case of NGr-3, a slightly higher concentration of 6.85 wt% was obtained. The electrochemical studies performed with NGr modified electrodes proved that the charge-transfer resistance (Rct) and the apparent heterogeneous electron transfer rate constant (Kapp) depend not only on the nitrogen doping level but also on the type of nitrogen atoms found at the surface (pyrrolic-N, pyridinic-N or graphitic-N). In our case, the NGr-1 sample which has the lowest doping level and the highest concentration of pyrrolic-N among all nitrogen-doped samples exhibits the best electrochemical parameters: a very small Rct (38.3 Ω), a large Kapp (13.9 × 10−2 cm/s) and the best electrochemical response towards 8-hydroxy-2′-deoxyguanosine detection (8-OHdG).

Highlights

Graphene, a single layer of graphite, possesses various interesting properties such as large surface area, high thermal and electrical conductivity and good optical transparency [1,2,3]
The electrochemical studies performed with N doped graphene (NGr) modified electrodes proved that the charge-transfer resistance (Rct ) and the apparent heterogeneous electron transfer rate constant (Kapp ) depend on the nitrogen doping level and on the type of nitrogen atoms found at the surface
We present for the first time the influence of the reaction time on the morphology, structure and electrochemical properties of nitrogen-doped graphenes

Summary

Introduction

A single layer of graphite, possesses various interesting properties such as large surface area, high thermal and electrical conductivity and good optical transparency [1,2,3]. The chemical doping of graphene is an active area of research which continues to grow very quickly. Doping graphene with heteroatoms such as nitrogen [4,5], boron [6,7], sulfur [8,9] or halogens [10,11] can adjust the electronic and electrochemical properties of the material leading to enhanced performances. Nitrogen has drawn a lot of attention due to the significantly improved properties of the N-graphene as part of fuel cells [12], lithium ion batteries [13], supercapacitors [14] or advanced catalyst support [15,16].

Methods

Results

Conclusion