Abstract
The high specific surface area of multilayered two-dimensional carbides called MXenes, is a critical feature for their use in energy storage systems, especially supercapacitors. Therefore, the possibility of controlling this parameter is highly desired. This work presents the results of the influence of oxygen concentration during Ti3AlC2 ternary carbide—MAX phase preparation on α-Al2O3 particles content, and thus the porosity and specific surface area of the Ti3C2Tx MXenes. In this research, three different Ti3AlC2 samples were prepared, based on TiC-Ti2AlC powder mixtures, which were conditioned and cold pressed in argon, air and oxygen filled glove-boxes. As-prepared pellets were sintered, ground, sieved and etched using hydrofluoric acid. The MAX phase and MXene samples were analyzed using scanning electron microscopy and X-ray diffraction. The influence of the oxygen concentration on the MXene structures was confirmed by Brunauer-Emmett-Teller surface area determination. It was found that oxygen concentration plays an important role in the formation of α-Al2O3 inclusions between MAX phase layers. The mortar grinding of the MAX phase powder and subsequent MXene fabrication process released the α-Al2O3 impurities, which led to the formation of the porous MXene structures. However, some non-porous α-Al2O3 particles remained inside the MXene structures. Those particles were found ingrown and irremovable, and thus decreased the MXene specific surface area.
Highlights
Since the discovery of graphene [1], the scientific trend in nanomaterial sciences turned toward two-dimensional (2D) nanostructures
We investigated and explained the influence of oxygen concentration during MAX phase preparation on the formation of alumina particles during MAX phase sintering, and on the properties of derived MXenes
High concentrations of O2 molecules adsorbed on TiC/Ti2 AlC particles or inside the cold-pressed pellet led to the increased formation of α-Al2 O3 particles in the Ti3 AlC2 matrix
Summary
Since the discovery of graphene [1], the scientific trend in nanomaterial sciences turned toward two-dimensional (2D) nanostructures. The delamination of Ti3 C2 Tx toward single-layers led to an increase in the specific surface area (SSA) and allowed for one of the highest volumetric capacitances (520 F/cm at 2 mV/s), which exposed them as a potential candidate for electrical double layer capacitors [7] Thanks to their lamellar structure, conductive core and hydrophilic surface, MXenes can host many different cations between their layers. In our work we took a totally different approach and investigated the possibility of controlling the porosity and specific surface area of multilayered Ti3 C2 Tx MXenes at the pre-formation stage—during the preparation of the Ti3 AlC2 MAX phase. The environmental oxygen concentration during MAX phase preparation had a significant influence on the amount of Al2 O3 impurities in different MXene samples, and on their porosity and specific surface area
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