Drexel researchers demonstrate intercalation of MXenes with a variety of ions; high volumetric capacitance
Researchers at Drexel University with colleagues in France have demonstrated that titanium carbide (Ti3C2) “MXene” compounds—exfoliated 2D carbide and carbonitride nanosheets that are structurally similar to graphene, where M represents transition metals, and X is either C or/and N (earlier post)—support the spontaneous intercalation of cations from aqueous salt solutions. A variety of cations, including Na+, K+, NH4+, Mg2+, and Al3+, can also be intercalated electrochemically, offering capacitance in excess of 300 farads per cubic centimeter (much higher than that of porous carbons). A paper on their work is published in Science.
About three years ago, Dr. Michel W. Barsoum and Dr. Yury Gogotsi, professors in Drexel’s College of Engineering, discovered atomically thin, two-dimensional materials—similar to graphene—that have good electrical conductivity and a surface that is hydrophilic, or can hold liquids. They named these new materials “MXenes,” which hearkens to their genesis through the process of etching and exfoliating atomically thin layers of aluminum from layered carbide “MAX phases.” (The latter also discovered at Drexel about 15 years ago by Barsoum.)
In the latest paper, Gogotsi and Barsoum along with Drexel researchers Maria Lukatskaya, Olha Mashtalir, Chang Ren, Yohan Dall’Angese and Michael Naugib and Patrick Rozier, Pierre Louis Taberna and Dr. Patrice Simon from Université Paul Sabatier in France, explain how MXenes can accommodate various ions and molecules between their layers by intercalation.
Intercalation is sometimes a necessary step in order to exploit the unique properties of two-dimensional materials. For example, placing lithium ions between the MXene sheets makes them good candidates for use as anodes in lithium-ion batteries. The fact that MXenes can accommodate ions and molecules in this way is significant because it expands their ability to store energy.
Currently, eight MXenes have been reported by our team, but there are likely many more that will be discovered—the MXene-and-ion combinations that have been tested to date are by no means an exhaustive demonstration of the material’s energy storage capabilities. So even the impressive capacitances that we are seeing here are probably not the highest possible values to be achieved using MXenes. Intercalation of magnesium and aluminum ions that we observed may also pave the way to development of new kinds of metal ion batteries.—Yury Gogotsi
Barsoum and Gogotsi’s report looks at intercalation of MXenes with a variety of ions, including lithium, sodium, magnesium, potassium, ammonium and aluminum ions. The resulting materials show high energy storage capacities and present another avenue of research in this branch of materials science.
Two-dimensional, titanium carbide MXene electrodes show excellent volumetric super capacitance of up to 350 F/cm3 due to intercalation of cations between its layers. This capacity is significantly higher than what is currently possible with porous carbon electrodes. In other words, we can now store more energy in smaller volumes, an important consideration as mobile devices get smaller and require more energy.—Michel Barsoum
The researchers also reported on using MXene “paper” electrodes, instead of conventional rolled powder electrodes with a polymer binder. The flexibility of this paper suggests MXenes may also be useful in flexible and wearable energy storage devices, which is another major area of ongoing research at Drexel in collaboration with Professor Genevieve Dion’s Shima Seiki Haute Technology Laboratory.
Maria R. Lukatskaya, Olha Mashtalir, Chang E. Ren, Yohan Dall’Agnese, Patrick Rozier, Pierre Louis Taberna, Michael Naguib, Patrice Simon, Michel W. Barsoum, and Yury Gogotsi (2013) Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide. Science 341 (6153), 1502-1505 doi: 10.1126/science.1241488