Nitrogen-doped graphenic foam synthesized by solvothermal-based process: Effect of pyrolysis temperature on the material properties

Abstract

Extraordinary properties of graphenic materials no longer need to be demonstrated. Nitrogen doping has been known to broaden the graphene application fields, especially for catalysis purposes. The present work reports a solvothermal-based process for the synthesis of a nitrogendoped graphenic foam with up to 2.6 at.% nitrogen, exhibiting the inherent properties of graphenic materials with high textural properties and surface areas as high as 2243 m².g-1. This study aims to give a better understanding of the influence of the pyrolysis treatment on the properties of the produced material for optimization of the synthesis in view to fuel cell applications. Several cross-linked techniques such as transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, nitrogen physisorption at 77 K and X-ray photoelectron spectroscopy have been employed to give a complete, precise characterization of the elaborated N-doped graphenic foams, leading to optimized conditions for the pyrolysis step. Pyrolysis at 850 °C has been found to allow the best compromise in terms of purity, homogeneity and crystallinity, with high fractions of pyrrolic, pyridinic and graphitic Nsubstitution that are known to greatly enhance the material catalytic properties. An oxidative degradation process was also evidenced for temperatures above 875 °C, leading to far lower graphene amounts.

Investigation of and mechanism proposal for solvothermal reaction between sodium and 1-(2-hydroxyethyl)piperidine as the first step towards nitrogen-doped graphenic foam synthesis

“…Change in pressure from 100 bar to 200 bar was not associated with meaningful variation in the solvothermal product. However, as was mentioned in a previous work, 33 the pyrolysis of solvothermal products from 100 bar reactions led to only poorly organized graphenic materials. This could mean that the solvothermal pressure has an impact on the structure and microstructure of the solvothermal product, but it could not be investigated as the synthetized products are unstable under the electronic beam.…”

“…The solvothermal reaction pressure was varied between 100 bar and 200 bar, a range which has been proved suitable for synthesis of high-quality graphenic materials in previous works. 33 Once the autoclave was sealed, nitrogen (Air Liquide, Alphagaz 2) was introduced so that the internal pressure at the reaction temperature could reach the desired level of 100 bar or 200 bar. The reactor was then heated to the target temperature at 8 1C min À1 and the internal pressure reached the desired value.…”

“…31 However, the formation of chlorine-derived gases could be avoided by changing the reagents and reaction conditions. In a previous study, 33 a solvothermal-based process using a mixture of cyclohexanol, ethanolamine and sodium was developed for the synthesis of good quality nitrogen-doped graphenic foam, whose extensive characterization revealed high surface area, good crystallinity and promising catalytic properties. Moreover, this study allowed determination of the optimal temperature of pyrolysis, 850 1C, to yield N-doped graphenic foams with the best compromise between homogeneity, purity and crystallinity, along with appreciable synthetic yields.…”

Metal-free nitrogen-doped graphenic materials as cathode catalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells

“…Before presenting the results of the present work, properties of CE materials extensively characterized [27] are summarised below. CE materials obtained by pyrolysis at 850°C or more, exhibited a high crystallinity, as expressed by narrow bands D and G in Raman spectra.…”

“…In a previous work [27], the experimental conditions used for the elaboration of the N-doped graphenic materials have been shown to have a great impact on their textural, structural, microstructural, and chemical properties. In particular, changing the temperature for the pyrolysis treatment allows tailoring of the material properties.…”