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

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.

Nitrogen doped carbonaceous materials as platinum free cathode electrocatalysts for oxygen reduction reaction (ORR)

“…The spectrum measured on the N-MLG (curve (a)) is essentially identical to that reported previously in the literature [50]. It can be modeled by two main contributions: a weaker one at 398.3 eV binding energy, arising from pyridinic N and a stronger one at 399.4 eV attributed to pyrrolic N [50] and/or diazine/triazine-like aromatic environments or aromatic amine functionalities [67]. As melamine has indeed a relatively broad N 1s spectrum with its main contribution around 399.4 eV due to its aromatic amines [76] assignation of the 399.4 eV N 1s peak of N-MLG to melamine-related groups rather than to pyrrolic N seems to be more appropriate.…”

“…5. The spectrum measured on the N-MLG (curve (a)) is essentially identical to that reported previously in the literature [50]. It can be modeled by two main contributions: a weaker one at 398.3 eV binding energy, arising from pyridinic N and a stronger one at 399.4 eV attributed to pyrrolic N [50] and/or diazine/triazine-like aromatic environments or aromatic amine functionalities [67].…”

“…As melamine has indeed a relatively broad N 1s spectrum with its main contribution around 399.4 eV due to its aromatic amines [76] assignation of the 399.4 eV N 1s peak of N-MLG to melamine-related groups rather than to pyrrolic N seems to be more appropriate. Apart from these strong features, a weak band around 405 eV arises from oxidized N species [50]. In case of the N-GO sample (spectrum (b)) the relative intensity of the pyridinic N signal (shifted to slightly lower binding energy at 397.9 eV) was higher than that for the other two materials.…”

“…N-doped multilayer graphene (N-MLG) was prepared as in our previous work [50]. Briefly, 1 g of graphite and 3 g of melamine were loaded in a stainless-steel grinding jar together with 30 grinding balls (10 mm diameter, made of stainless steel) then the mixture was ground at 400 rpm for 24 h. The process was performed at room temperature.…”

Preparation of Pt electrocatalyst supported by novel, Ti(1−x)MoxO2-C type of composites containing multi-layer graphene

“…Although direct synthesis routes of graphene from graphite have several drawback in general [30], the mechanical ball milling procedure is considered as accessible and green approach to produce few layer graphene [31]. Ball milling has also given possibility to prepare N-doped graphene from graphite in order to use as electrocatalysts [32,33]. Preparation of halogenated graphene nanoplatelets (GNP) for metal-free electrocatalyst by use of ball milling of graphite has also been described [34].…”