Vertical Ti₃C₂T_x MXene Nanosheets under an Alternating Current Electric Field

Aligning atomically thin two-dimensional materials vertically to the bottom has received much attention to utilize its structural anisotropy. In particular, various strategies have been reported to achieve vertical MXene, early transition metal carbide and nitride, for high capacitive performance. However, controlling the azimuthal orientation of the vertical MXene nanosheets cannot be achived with the previous methods, so its application was limited predominantly to capacitors. Here, vertical alignment induced by applying an alternating electric field to MXene colloid is presented. The reversible alignment switching of the colloid depending on the ON and OFF states of the electric field is observed through a polarized optical microscope. The immobilized nanosheets maintaining the colloidal orientation under the electric field can be obtained through in-situ freeze-drying. The oriented vertical MXene nanosheets exhibit an anisotropic electrical conductivity with a difference of nearly 9 times depending on the direction. In addition, various patterns composed of vertical MXenes are devoloped using diversified electrode designs. Based on these results, a new paradigm is suggested for various applications of vertical MXene such as sensors, optical polarizers, and heat-dissipating films, not limited to high-performance storage batteries.