Graphene production by cracking

Abstract

In recent years, graphene has found its use in numerous industrial applications due to its unique properties. While its impermeable and conductive nature can replace currently used anticorrosive toxic pigments in coating systems, due to its large strength to weight ratio, graphene can be an important component as a next-generation additive for automotive, aerospace and construction applications. The current bottlenecks in using graphene and graphene oxide and other two-dimensional materials are the availability of cost-effective, high-quality materials and their effective incorporation (functionalization and dispersion) into the product matrices. On overcoming these factors, graphene may attract significant demands in terms of volume consumption. Graphene can be produced on industrial scales and through cost-effective top-down routes such as chemical, electrochemical and/or high-pressure mechanical exfoliation. Graphene, depending on end applications, can be chemically tuned and modified via functionalization so that easy incorporation into product matrices is possible. This paper discusses different production methods and their impact on the quality of graphene produced in terms of energy input. Graphene with an average thickness below five layers was produced by both methods with varied defects. However, a higher yield of graphene with a lower number of layers was produced via the high-pressure exfoliation route. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.

Keywords: 2D materials; energy storage; graphene; graphene oxide; graphene production; transistors.

Figure 1.

Two types of mechanical force to separate graphite layers [22]. (a) The mechanism of liquid-phase exfoliation and (b) mechanism of sonication exfoliation [22]. (Online version in colour.)

Figure 2.

Three layers of graphene connected weakly bonded van der Waals forces. (Online version in colour.)

Figure 3.

The mechanism of electrochemical exfoliation in two different electrolytes. (a) Lithium intercalation exfoliation (50) and (b) sulfonate salt solution [33]. (Online version in colour.)

Figure 4.

Graphene dispersions (a) electrochemical exfoliation using the high purity materials (Ceylon graphite) compressed as electrode pellets (b) high-pressure exfoliation of exfoliated graphene (Ceylon graphite). (Online version in colour.)

Figure 5.

X-ray diffractogram of high purity Ceylon vein graphite (C-99.995%).

Figure 6.

(a) Raman spectra of high pressure exfoliated graphene. (b) Raman spectra of electrochemical exfoliated graphene.

Figure 7.

(a) Scanning electron micrograph of diluted high-pressure exfoliated diluted few-layer graphene. (b) Scanning electron micrograph of diluted electrochemically exfoliated few-layer graphene.

Figure 8.

(a) FEG-TEM of electrochemical exfoliated multi-layer graphene. (b) SAED pattern of exfoliated multi-layer graphene.

Figure 9.

(a) FEG-TEM of high pressure exfoliated few-layer graphene; (b) SAED pattern of exfoliated few-layer graphene (c) HR-TEM image of exfoliated graphene showing few layers.

Figure 10.

XPS survey spectra of the high pressure exfoliated few-layer graphene.