MXene’s Path to Revolutionizing Energy Storage and More

Fabrication of electrically conductive porous silica via infiltration of 2D MXene nanosheets. a) Preparation of silica disks with unidirectional porosity by freezing. The blue arrows represent the direction of solidification and the main orientation of the pores. SEM images show the horizontal (top) and vertical (bottom) cross sections of the fabricated porous samples (scale bar = 100 µm). b) A sample of MXene-infiltrated porous silica with an enlarged 3D figure showing thin-film coating of internal pore surfaces by MXene flakes while preserving structural porosity. A high-magnification backscattered SEM image of an infiltrated sample shows the thin-film coating of MXene (scale bar = 10 µm). c) MXene dispersion prepared using minimum intensity layer delamination (MILD) method. d) The hydrodynamic distribution of 2D Ti diameters3VS2TX nanosheets for prepared MXene dispersion. A solid model of the dispersed 2D flakes is given in the inset. e) TEM image showing the structure and size of a single-layer Ti3VS2TX nanosheet with arrows indicating its periphery. False coloring (purple) is used for ease of viewing. f) Results of thermogravimetric analysis (TGA) of the remaining mass of MXene dispersion as a function of temperature. The mass value at 200°C is used to calculate the MXene concentration of the dispersions. Credit: Advanced materials (2023). DOI: 10.1002/adma.202304757

Boasting many impressive properties, transition metal carbides, commonly referred to as MXenes, are exciting nanomaterials being explored in the energy storage sector. MXenes are two-dimensional materials made up of flakes as fine as a few nanometers.

Their exceptional mechanical strength, ultra-high surface-to-volume ratio and superior electrochemical stability make them promising candidates as supercapacitors, that is, provided they can be arranged in 3D architectures where there is a sufficient volume of nanomaterials and where their large surfaces are available for reactions.

During processing, MXenes tend to re-stack, compromising accessibility and hindering the performance of individual flakes, thereby diminishing some of their significant benefits. To get around this obstacle, Rahul Panat and Burak Ozdoganlar, along with Ph.D. candidate Mert Arslanoglu, from the Department of Mechanical Engineering at Carnegie Mellon University, developed a completely new materials system that organizes 2D MXene nanosheets into a 3D structure.

This is accomplished by infiltrating MXene into a porous ceramic scaffold or structure. The ceramic skeleton is fabricated using the freeze casting technique, which produces open-pore structures with controlled pore dimensions and directionality.

The study is published in the journal Advanced materials.

“We are able to infiltrate solvent-dispersed MXene flakes into a frozen porous ceramic structure,” explained Panat, a professor of mechanical engineering. “As the system dries, the 2D MXene flakes evenly coat the internal surfaces of the ceramic’s interconnected pores without losing any essential attributes.”

As described in their previous publication, the solvent used in their freeze casting approach is a chemical called camphene, which produces tree-like dendritic structures when frozen. Other types of pore distributions can also be obtained using different solvents.

To test the samples, the team built two-electrode “sandwich” supercapacitors and connected them to an LED light with an operating voltage of 2.5 V. The supercapacitors successfully powered the light with values higher power density and energy density than previously achieved for all MXene-based supercapacitors.

“Not only have we demonstrated an exceptional way to use MXene, but we have done it in a way that is reproducible and scalable,” said Ozdoganlar, also a professor of mechanical engineering. “Our new material system can be mass-produced to desired dimensions for use in commercial devices. We believe this can have a significant impact on energy storage devices and therefore applications such as electric vehicles. ”

With exceptional experimental results and electrical conductivity that can be finely tuned by controlling MXene concentration and backbone porosity, this material system shows considerable potential for batteries, fuel cells, decarbonization systems and catalytic devices . We may even one day see an MXene supercapacitor powering our electric vehicles.

“Our approach can be applied to other nanoscale materials, such as graphene, and the skeleton can be constructed from materials other than ceramics, including polymers and metals,” Panat said. “This structure could enable a wide range of emerging and new technological applications.”

More information:
Mert Arslanoglu et al, 3D assembly of MXene networks using a ceramic skeleton with controlled porosity, Advanced materials (2023). DOI: 10.1002/adma.202304757

Provided by Carnegie Mellon University Mechanical Engineering

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