Eco-Friendly Nitrogen-Doped Graphene Preparation and Design for the Oxygen Reduction Reaction.

Monica Dan,Sebastian A Porav,Adriana Vulcu,Camelia Berghian-Grosan,Oana Cadar,Cristian Leostean,Gheorghe Borodi

doi:10.3390/molecules26133858

Abstract

Four N-doped graphene materials with a nitrogen content ranging from 8.34 to 13.1 wt.% are prepared by the ball milling method. This method represents an eco-friendly mechanochemical process that can be easily adapted for industrial-scale productivity and allows both the exfoliation of graphite and the synthesis of large quantities of functionalized graphene. These materials are characterized by transmission and scanning electron microscopy, thermogravimetry measurements, X-ray powder diffraction, X-ray photoelectron and Raman spectroscopy, and then, are tested towards the oxygen reduction reaction by cyclic voltammetry and rotating disk electrode methods. Their responses towards ORR are analysed in correlation with their properties and use for the best ORR catalyst identification. However, even though the mechanochemical procedure and the characterization techniques are clean and green methods (i.e., water is the only solvent used for these syntheses and investigations), they are time consuming and, generally, a low number of materials can be prepared, characterized and tested. In order to eliminate some of these limitations, the use of regression learner and reverse engineering methods are proposed for facilitating the optimization of the synthesis conditions and the materials’ design. Thus, the machine learning algorithms are applied to data containing the synthesis parameters, the results obtained from different characterization techniques and the materials response towards ORR to quickly provide predictions that allow the best synthesis conditions or the best electrocatalysts’ identification.

Highlights

Nitrogen-doped graphene (N-doped graphene, N-Gr), obtained by the substitution of carbon atoms from the graphene layers with nitrogen, possesses interesting structure and electronic, magnetic and optical properties [1,2,3]
The graphene obtained by ball milling procedure appears to have a fluffy structure, very different from that synthetised by chemical vapor deposition (CVD) or chemical methods [14,19,20] or the graphite structure (Figures 1 and S1, Supplementary Materials)
By a green and scalable method, four types of N-doped graphene materials with a nitrogen content ranging from 8.34 to 13.1 wt.%. These materials have been tested towards oxygen reduction reaction (ORR) by cyclic voltammetry and rotating disk electrode protocols and their electrochemical responses have been compared with the results obtained from the surfaces and chemical investigation techniques

Summary

Introduction

Nitrogen-doped graphene (N-doped graphene, N-Gr), obtained by the substitution of carbon atoms from the graphene layers with nitrogen, possesses interesting structure and electronic, magnetic and optical properties [1,2,3]. Due to the atomic size similarity of the carbon and nitrogen atoms, N-doping of the graphene sheets can be produced by direct synthesis when chemical vapor deposition (CVD), segregation growth, solvothermal or arc-discharge approaches are considered, or by post-synthesis techniques such as thermal, plasma or hydrazine treatments [4]. Using these methods, several N-bonding configurations are attained in the N-doped graphene structure; the four common configurations are.

Methods

Results

Conclusion