Comparing the Future of Graphene and MXenes in Flexible Electronics
Electronic components and circuits are evolving towards more elastic and flexible platforms. Formulations using innovative nanomaterials have been created to fuel the search for more environmentally friendly, durable and cost-effective conductive inks for coating flexible platforms.
Study: Coatings of Electrically Conductive 2D Materials for Flexible and Stretchable Electronics: A Comparative Review of Graphenes and MXenes. Image Credit: Mopic/Shutterstock.com
A review article published in the journal Advanced functional materials highlights the important characteristics of conductive inks and two-dimensional (2D) materials, in particular graphene and MXenes.
Flexible materials for electronic systems
Advances in elastic, wearable, and biocompatible electronic technologies depend on the creation and adoption of lightweight, inexpensive electronic circuits and optoelectronic systems that consume little power and can operate in a variety of situations. The endurance to mechanical stresses of the systems and their constituent materials is also important.
Printed circuit boards (PCBs) are fundamental and ubiquitous components of most electronic systems. PCBs provide mechanical support and electrical bonding to electronic circuits using conductive channels or signal traces.
A PCB is a thin panel made of poly-epoxies and fiberglass, covered with thin sheets of copper. However, the stiffness differential between the platforms and the electronic connection makes this method unsuitable for use with elastic and flexible substrates.
The focus of recent studies has therefore shifted to the development of conductive inks for coating and decorating electronic circuits on flexible materials that can bend with the platform while remaining attached to it, and retain their Electrical Specifications.
Benefits of using non-metallic inks
Although non-metallic inks have a higher electrical resistance than metallic inks, they still offer significant advantages.
A post-coating process is usually required for conductive ink applications, which can damage typical flexible polymer platforms. Non-metallic inks do not require this process.
The distribution of these inks is generally simpler, allowing the development of a conductive ink that is stable over time. There are some instances where these inks can be biocompatible, allowing for smoother processing and a myriad of uses.
Non-metallic inks cost significantly less than inks containing precious metal particles like silver (Ag) and gold (Au). Formulating such inks is generally a relatively simple process. Fewer solvents are needed for their production and the solvents used, such as alcohol or water, are harmless to humans and the environment.
Conductive inks based on 2D materials
Electrically conductive inks with two-dimensional material formulations have attracted the interest of researchers due to the advantages provided by their flake-like morphology and large aspect ratio.
These inks exhibit high optical transmission and electrical conductance in thin sheet coatings on transparent and stretchable polymer platforms, allowing them to be used in flexible and transparent electronic systems.
These conductive inks exhibit good adhesion to a wide range of foams and fabrics, generating conductive frameworks of nanoplatelet layers that can slide over each other. This phenomenon gives remarkable micromechanical qualities to conductive armatures, allowing them to be used for pressure and strain measurement.
Different types of two-dimensional materials
The ever-growing collection of solution-processable two-dimensional materials includes conductive materials like graphene, semiconductor materials like molybdenum disulfide or tungsten disulfide, and insulators like graphene oxide or boron nitride hexagonal.
MXenes are a class of electrically conductive two-dimensional transition metal nitrides/carbides. MXenes can integrate the lower resistivity values of metallic inks with the shape of nanoplatelets and the ease of processing of two-dimensional inks, making them highly desirable materials.
Advantages of flexible coatings
Conductive elastic films can be used directly for applications such as EMI shielding or modulated for specific use cases such as heating or sensing.
Additionally, conductive coatings can be designed to use conductive structures for various applications such as interdigital electrodes (IDE) in supercapacitors (SC) or strain gauges.
The use of asymmetric and hybrid SC electrodes in coplanar, cofacial or fibrous configurations has resulted in various flexible supercapacitors and micro-supercapacitors that use MXenes and graphene.
MXenes versus Graphene
MXenes are becoming increasingly popular as they incorporate good electrical conduction with processing capability and crucial morphological advantages.
MXenes share the advantageous qualities of graphene, such as good electrical conduction, two-dimensional architecture, and excellent adhesion to substrate materials, without being hindered by some of the disadvantages of graphene-based materials.
MXenes do not require chemical or thermal reduction mechanisms that are otherwise required for graphene oxide. Moreover, unlike graphene nanoparticles, Mxenes exhibit rapid dispersion in aqueous media without the need for additives.
In Joule heaters, for example, this results in lower potential demands to reach the appropriate temperatures than graphene, even rivaling metallic nanomaterials. In EMI shielding, the increased conductivity of MXenes allows for greater signal attenuation at a thickness similar to graphene.
The tendency of MXenes to experience oxidation and electrical deterioration, even inside polymer frames, may require further research to engineer robust surface features and larger side sizes.
Reference
Orts, V., Chan, KC, Caironi, M., Athanassiou, A., Kinloch, IA, Bissett, M. and Cataldi, P. (2022). Coatings of Electrically Conductive 2D Materials for Flexible and Stretchable Electronics: A Comparative Review of Graphenes and MXenes. Advanced functional materials. Available at: https://onlinelibrary.wiley.com/doi/10.1002/adfm.202204772