ACS AMI: cryopreservation of aqueous MXenes dispersion

As a new class of 2D nanomaterials, MXenes has attracted increasing attention due to its metal conductivity, good solution processability and outstanding energy storage performance. MXene combines the 2D conductive carbide layer with hydrophilicity, mainly due to the presence of surface hydroxyl groups. Up to now, nearly 30 MXenes have been successfully synthesized, including Ti3C2Tx, Ti2CTx and Nb4C3Tx. Among the many MXenes, Ti3C2Tx is the most studied one because it has the highest capacitance (~1500 F cm-3) and outstanding metal conductivity (~15000 S cm-1) among supercapacitors. Although MXene has many advantages, its main limitation lies in its poor oxidation resistance, especially when nanosheets are exposed to oxygen-containing water for a long time, they will quickly be oxidized to TiO2. After oxidized MXenes, the electronic conductivity will be greatly reduced, and the reaction interface will be passivated, thereby reducing the energy storage performance. Therefore, maintaining the integrity of MXene nanosheets is essential for some MXene aqueous solutions, such as filtration membranes, wet-spun fibers, hydrogel/aerogel preparation, and water-based supercapacitors.

Recently, Professor Joselito M. Razal from Deakin University in Australia published a research paper entitled Freezing Titanium Carbide (MXenes) Aqueous Dispersions for Ultra-long-term Storage in the internationally renowned academic journal ACS Applied Materials & Interfaces. The paper found a low temperature The method of freezing the aqueous MXene dispersion can effectively prevent the formation of TiO2 at the edges of the nanosheets in the early stage of oxidation. Compared with the newly synthesized MXene, the Ti3C2Tx nanosheets in the frozen dispersion can maintain the same morphology and elemental composition during the shelf life of more than 650 days.

Figure 1. Schematic diagram of the oxidation process of Ti3C2TxMXene tablets in the dispersion.
 
 

Figure 2. Morphology and structure characterization of Ti3C2TxMXene sheet.
 
 

Figure 3. Electrochemical performance test of each corresponding electrode.
 

Figure 4. MXene tensile strain curve under different conditions; voltage-current response; XRD; SEM image of MXene film interface.

Figure 5. Electrochemical performance test of MXenes under different conditions.
 

In this article, the researchers used a method of cryopreserving Ti3C2TxMXene aqueous dispersion to evaluate the relationship between the oxidation process of MXene in water and temperature. The morphology and performance of the newly synthesized MXene, the frozen MXene and the MXene dispersion stored at room temperature were analyzed, and the following conclusions were drawn: TiO2 nanoparticles will be oxidized and formed at room temperature the next day, but the frozen dispersion is only weak The oxidation occurs. It is worth mentioning that the freeze-dried MXene nanosheets will retain the morphology and physical properties of the sheet, such as electronic conductivity, mechanical properties and energy storage performance even after being stored for 650 days. These results prove that cryopreserved MXene dispersion is a simple and effective way, which can be used for long-term storage of MXene aqueous dispersion.
Literature link:
DOI: 10.1021/acsami.0c06728
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