Amongst two-dimensional graphene analogous materials, transition metal carbides are reported to be a highly promising material for energy storage devices. Their high electrical conductivity, thermal stability, surface area and surface chemical properties induce high volumetric capacitance when developed into devices.
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Graphene has been a wonder material showing numerous appealing properties in one atom thick two-dimensional layer. It has found its huge application in energy storage devices such as batteries and supercapacitors due to its high mechanical flexibility, electrical conductivity, surface-to-volume ratio, ionic conductivity and theoretical capacitance. The specific roles of graphene in these devices were categorized as active materials, flexible supports, and electrically conductive additives.
Graphene-Based Electrodes and Market Survey
Graphene’s properties are reported to be highly dependent on the synthesis process adopted that altered the number of graphene layers in a stack, layer size, defects in the layer, wrinkles, surface functionalized groups and so on. These alterations further produce a huge variation in the material properties hence the device performances1.
A recent market survey from 2019 to 2021 on the graphene battery market published in “Fortune Business Insights” 2022, reports a boost in the market for graphene-enhanced batteries.
The report notes an increased demand for consumer electronics and electric vehicles. This increased demand further enhanced the government's research and development funding for graphene battery research. However, a breakthrough in research that could bridge the gap between lab-scale graphene research and practical applications is yet to come2.
The quantum confinement of charges in two-dimensional materials imparts unmatched properties compared to their other dimensional counterparts. Two-dimensional graphene analog materials have reported high surface-to-volume ratio, increased number of active sites and good electric conductivity. They exhibited increased reaction kinetics during the charging and discharging when used in electrochemical storage devices 3.
A high theoretical storage capacitance of 744 mAhg-1 for the lithium-ion battery comprising graphene sheets was reported. The performances of graphene-based energy storage systems are reported to be varying with the change in the morphology of the graphene sheets. Experimental work on different graphene sheets-based electrode layers such as single, triple and quintuplicate layers were reported as 1,175, 1,007 and 842 mA.h.g-1, respectively1.
Surface modification of graphene sheets through heteroatom doping, for example, nitrogen and boron were reported to tune the surface properties of graphene, resulting in enhanced reversible capacitance of 1,040 mA.h.g-1. Many other techniques were developed to modify graphene sheets to increase the storage efficiency of the electrochemical storage devices.
Graphene Analogues Materials for Energy Storage
Many graphene analogs two-dimensional materials such as metal sulfides, transition metal dichalcogenides, transition metal oxides, transition metal carbides, transition metal nitrides, silicenes and phosphorene have reported good performances as active electrode materials in electrochemical storage devices.
Transition Metal Carbides, a Promising Material
Two-dimensional carbides, with their superior electrochemical cycle stability, low cost, hydrophilicity and high capacity and efficiency, are one of the materials on which large investigation is carried on for developing electrodes. Studies were reported on both the positive and negative electrodes in electrochemical storage devices.
Two-dimensional metal carbides and nitrides, commonly known as MXenes, were reported as electrode materials and conductive adhesives for energy storage devices such as lithium-ion batteries (LIB), sulfur-ion batteries (SIB), lithium-sulfur batteries (LSB) and supercapacitors4.
It was reported on the basis of calculated theoretical gravimetric capacity, which is a measure of the amount of charge stored in a gram of the material; transition metal carbides with low molecular weight are the most promising materials for energy storage applications. Materials such as Titanium carbide (Ti2C), Niobium Carbide (Nb2C), Vanadium carbide (V2C) and Scandium Carbide (Sc2C) are a few among them5.
Surface functionalization and interlayer spacing engineering of transition metal carbides are one of the techniques that are being explored for enhancing its electrochemical performance. Ti3C2Tx are the categories explored much for their application in capacitors. In work by Ghidiu et al., it was reported that the volumetric capacitance of free-standing Ti3C2Tx paper electrodes was 300-400 F.cm-3. The reported values exceeded those reported by all carbon based electrical double-layer capacitors6.
Hybridization of transition metal carbides with carbon-based materials has been reported to enhance electrochemical and mechanical performances. In work by Mashtalir et al., they have reported improved capacity and stability of the LIBs and capacitors employing electrodes having transition metal carbides hybridized with 5-10 weight % of carbon nanotubes, graphene and onion-like carbon7.
Future of Transition Metal Carbides in Energy Storage
The synthesis process of transition metal carbides results in a well-dispersed and stable colloidal solution that increases its ease of material processability in applications such as printed electrodes, and the development of coatings and films.
High electronic conductivity and the presence of redox active transition metal atoms in the 2D transition metal carbides make them very suitable for electrode application in energy storage devices.
These materials reported excellent volumetric capacitances in different electrolyte set-up, such as in sulfuric acid electrolytes, aqueous electrolytes, ionic and inorganic liquid electrolytes. The pseudo-capacitance reported in these materials could be developed to acquire high energy density at higher charging rates.
Many 2D transition metal carbides that have been discovered are yet to be explored as electrode materials in electrochemical energy storage devices. Better analysis and understanding of the ion transport dynamics in-between the layers of 2D transition metal carbides could lead to the development of efficient batteries and supercapacitors.
Reference and Further Reading
Dong, Y., Wu, Z.S., Ren, W., Cheng, H.M. and Bao, X., (2017). Graphene: a promising 2D material for electrochemical energy storage. Science Bulletin, 62(10), pp.724-740.
https://www.fortunebusinessinsights.com/graphene-battery-market-105711
Zhang, X., Hou, L., Ciesielski, A. and Samorì, P., (2016). 2D materials beyond graphene for high‐performance energy storage applications. Advanced Energy Materials, 6(23), p.1600671.
Long, M.Q., Tang, K.K., Xiao, J., Li, J.Y., Chen, J., Gao, H., Chen, W.H., Liu, C.T. and Liu, H., (2022). Recent advances on MXene based materials for energy storage applications. Materials Today Sustainability, 19, p.100163.
Anasori, B., Lukatskaya, M.R. and Gogotsi, Y., (2017). 2D metal carbides and nitrides (MXenes) for energy storage. Nature Reviews Materials, 2(2), pp.1-17.
Ghidiu, M., Lukatskaya, M.R., Zhao, M.Q., Gogotsi, Y. and Barsoum, M.W., (2014). Conductive two-dimensional titanium carbide ‘clay’ with high volumetric capacitance. Nature, 516(7529), pp.78-81.
Mashtalir, O., Lukatskaya, M.R., Zhao, M.Q., Barsoum, M.W. and Gogotsi, Y., (2015). Amine‐assisted delamination of Nb2C MXene for Li‐ion energy storage devices. Advanced Materials, 27(23), pp.3501-3506.
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