Laser‐Induced Graphene

Ruquan Ye, James M. Tour

• Publisher: Jenny Stanford Publishing
• Year: 2020
• Print ISBN: 9789814877275
• eBook ISBN: 9781000091694
• Topic: Art
• Subtopic: Photography

LIG is a revolutionary technique that uses a common CO2 infrared laser scriber, like the one used in any machine shop, for the direct conversion of polymers into porous graphene under ambient conditions. This technique combines the preparation and patterning of 3D graphene in a single step, without the use of wet chemicals. The ease in the structural engineering and excellent mechanical properties of the 3D graphene obtained have made LIG a versatile technique for applications across many fields.

This book compiles cutting-edge research on LIG by different research groups all over the world. It discusses the strategies that have been developed to synthesize and engineer graphene, including controlling its properties such as porosity, composition, and surface characteristics. The authors are pioneers in the discovery and development of LIG and the book will appeal to anyone involved in nanotechnology, chemistry, environmental sciences, and device development, especially those with an interest in the synthesis and applications of graphene-based materials.

Chapter 1
Graphene: A Brief Overview

Graphene refers to a two-dimensional (2D) material consisting of 1-10 layers of carbon atom in a honeycomb structure. Since the first introduction of few-layer graphene (FLG) by mechanical exfoliation from graphite in 2004, research on graphene has been burgeoning and enormous breakthroughs in both fundamental and applied sciences have been achieved. While the manipulation of layered structures holds promise for the advancement of fundamental physics, in many practical applications, graphene is usually formed as a 3D structure, which offers high surface area while maintaining the intrinsic properties of graphene. In this chapter, we will first briefly introduce graphene as a material and then we present methods that have been developed for the preparation of 3D graphene embodiments that are foam-like in their structure.

1.1 From 2D Layers to 3D Assemblies

The discovery of graphene dates back to the 1960s when pioneer scientist Hanns-Peter Boehm first oxidatively exfoliated graphite to generate graphene oxide (GO) and then reduced it and showed its transmission electron microscopy (TEM) image, which appeared to be single layered, whereupon he coined the name “graphene” [1]. However, it was not until 2004, when Andre Geim and Konstantin Novoselov for the first time showed that monocrystalline FLG could be stable under ambient conditions and demonstrated its enormous electron mobility reaching as high as ~10,000 cm²/Vs [2]. It was this and many other extraordinary properties, both experimental and theoretical, that caused the explosive growth in the field. This led to the Nobel Prize in Physics being awarded to Geim and Novoselov in 2010, and it opened an era on the exploration of graphene and other 2D materials that were hitherto underappreciated for their stability and remarkable properties. In the early studies, many researchers were devoted to understanding the characteristics of graphene, such as mechanical strength, stiffness, and thermal and electrical conductivities. For example, in 2008, Hone et al. used an atomic force microscope to measure Young’s modulus and the intrinsic strength of monolayer graphene to be 1 TPa and 130 GPa, respectively [3]. In 2011, Geim et al. improved the microelectronic device structure and reported the electron mobility of graphene to be 25,000 cm²/Vs at room temperature [4]. In some cases, the properties approached their theoretical limits and were superior to many existing materials [5, 6]. By precisely controlling the layer structures, such as the number of stacking layers, the stacking angles, and the heteroatoms, researchers continued to discover more characteristics of graphene. For instance, in 2018, bilayer graphene with a magic twist angle of about 1.1° was found to have a relatively high superconducting critical temperature [7]. Given the large variety of control parameters, these results became a harbinger for the many breakthroughs in fundamental science that were to be realized.

The fascinating properties of graphene have attracted the interests of many industries, and it is expected that it will lead several next-generation technologies that were hitherto unattainable [8, 9]. For example, monolayer graphene has a high transparency while being highly conductive and mechanically strong, which makes it a prime candidate for use in flexible electronics [8].

However, in some cases, the graphene monolayer or few-layer structure alone was insufficient to provide for needed applications. Hence, the 2D layered graphene can be assembled into 3D foam-like structures [10]. This strategy is widely adopted in areas such as batteries, catalysis, sensors, and many composite materials. In this case, it maintains the electronic, mechanical, and chemical properties of graphene, while affording and accessible high surface area and large volume that are required for certain applications. For example, in comparison to graphite, a material that was commonly used as the anode in lithium-ion batteries, the use of 3D graphene materials can greatly improve the volumetric performance and cyclability of the same devices [11]. Therefore, there is ongoing interest in the development of new methods to manufacture 3D graphene in a scalable, economic, and environmentally friendly manner.

1.2 Development of Methodologies for 3D Graphene Synthesis

For the translation of the laboratory discovery of graphene to products, graphene needs to be cost-effectively manufactured on a larger scale, and 3D structures are no exception. So far, there have been many methods for preparation of 3D graphene foams, including chemical vapor deposition (CVD), mechanical exfoliation from graphite, liquid phase exfoliation, wet-chemistry redox processes, and others, followed by 3D structuring [9]. Each of the methods has its own advantages in the preparation of graphene of different grades at varied costs, which is an important advancement toward the commercialization of graphene. In general, the cost of CVD-growth graphene is higher, and the quality of the graphene is also higher, which can find applicability in advanced technologies such as flexible electronics, photonics, transistors, and future devices [8]. Exfoliations by means of chemical or electrochemical processes produce lower-grade graphene, but they are the most popular approaches for the preparation of graphene on a large scale [12, 13]. The exfoliated process from graphite usually affords FLG or graphene nanoplatelets (GNPs), and this material in 3D foams has found use in composites, catalysis, and heat dissipation platforms. Here we will introduce some conventional methods that have been reported for the synthesis of 3D graphene.

1.2.1 Chemical Vapor Deposition

Chemical vapor deposition is a method that is operated under high temperature and fine control of gas composition and pressure, through which carbon precursors decompose to form graphene on the surface of substrates. It has been extensively studied for the synthesis of 2D graphene with high crystallinity and fine control of layering. With thorough investigation, the effects of various factors, such as substrate, pressure, temperature, carbon precursors, pre-treatments, and post-transfer, in controlling the properties of graphene are now better understood [14]. Although this method is primarily aimed at replacing the “Scotch Tape” method for the scalable synthesis of 2D wafer-scale graphene, it can also be adapted for the synthesis of 3D graphene with the use of porous substrates (Fig. 1.1). For example, in 2011, Cheng et al. used commercially available nickel foam as the substrate and decomposed methane at 1000°C to form FLG on top of nickel [15]. The structure was then reinforced with a thin layer of poly(methyl methacrylate) (PMMA). Finally, the nickel and PMMA were etched sequentially with a hot HCl solution and acetone, respectively, for the formation of an interconnected graphene foam structure. The graphene foam was freestanding, low-density, and flexible.

Figure 1.1 Scheme of 3D graphene prepared by a CVD process. Adapted from Ref. [7]. Copyright © 2011, Springer Nature.

1.2.2 Assembly of Graphene Oxide

The reductive assembly of GO is one of the most popular methods for the preparation of 3D graphene due to its ease in large-scale preparation toward the formation of composites. The process, in general, involves two steps: one is the oxidation of graphite for the formation of GO where the graphene is oxidized, and the second is the reduction of GO for the regeneration of the graphene structure into a 3D form. For the first step, the oxidation of graphite can functionalize the graphene layer with oxygenated groups such as carboxyl, which helps to overcome the interlayer interaction and improves the dispersion in water. The synthesis of GO was first reported in 1859 by Brodie, who used potassium chlorate and fuming nitric acid to oxidize graphite [1]. This was improved by Staudenmaier in 1898, who added chlorate in multiple aliquots to alleviate the excessive heat from the oxidation reaction [16]. In 1958, Hummers further revised the protocol by using potassium permanganate and sodium nitrate in concentrated sulfuric acid, by which the side-product explosive gas ClO₂ could be eliminated [17]. In 2010, Tour replaced nitrate with phosphoric acid and added the permanganate in six aliquots [18]. This small change significantly improved the yield and made it a popular method for the preparation of GO; it also avoids the generation of toxic gases during the synthesis. The second step is the regeneration of graphene in 3D structure. This can be achieved by many approaches. For example, Yu reported a method by first assembling GO into an aerogel by a freeze-drying process and then thermally annealing the aerogel to remove the oxygenated functional...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• Preface
• Introduction
• 1. Graphene: A Brief Overview
• 2. Laser-Induced Graphene: Synthesis and Properties
• 3. Laser-Induced Graphene for Energy Storage
• 4. Laser-Induced Graphene for Electrocatalysis Applications
• 5. Laser-Induced Graphene for Water Treatment
• 6. Laser-Induced Graphene Sensors
• 7. Specific Laser Cutter Settings
• Index