Atomistic Insights of Ti-Based MXenes Thermal Decomposition and Transformation to Carbon-Supported Ti–O Phases for Energy Applications

Abstract

Ti–O phases combined with carbon materials are attractive for applications in energy storage, photocatalysis, and gas sensing. The oxidation of Ti-based MXenes at high temperatures has been proposed as an effective synthesis method for carbon-supported anatase and rutile TiO2. Here, the thermal degradation and phase transformation of Ti3C2T2 (T = O or OH) under vacuum, air, and water vapor environments are investigated using reactive molecular dynamics simulations. Ti3C2(OH)2 is most stable under vacuum and water vapor, and is least stable in air. In contrast, Ti3C2O2 shows the lowest stability in air. In the air environment, anatase and rutile TiO2 phases are found regardless of the surface termination, while in water vapor, the water molecules disrupt the formation of a distinct phase. Under vacuum, we observe the formation of rock-salt TiO and present a comprehensive analysis of its transformation. The phase transformation temperatures for Ti3C2O2 are 700, 600, and 700 K for vacuum, air, and water vapor environments, respectively. Ti3C2(OH)2 showed phase stability up to 1100, 600, and 900 K under vacuum, air, and water vapor environments, respectively. Our comprehensive atomistic analysis provides detailed descriptions of the thermal degradation process and phase transformation of Ti3C2T2, which helps to understand the nanoscale aspects of the experimental work.

The mechanism of room‐temperature oxidation of a HF‐etched Ti3C2TxMXene determined via environmental transmission electron microscopy and molecular dynamics

“…The calculation results show that Ti 3 C 2 (OH) 2 /O 2 system has an identical oxidation behavior with Ti 3 C 2 O 2 /O 2 system (Figures S15 and S16). The F surface groups are not taken in the work due to the fact that the parameterized F surface groups are not available in the current force fields 33 …”

“…The F surface groups are not taken in the work due to the fact that the parameterized F surface groups are not available in the current force fields. 33…”

Modeling and simulations for 2D materials: a ReaxFF perspective

“…Ti/C/O parameters were optimized against Ti-C bond, C-Ti-C, and C-Ti-O angle distortions and the energy of condensed phases. MX-2016 [36] was employed in [35,37,81,178,[186][187][188][189][190] for ReaxFF simulations.…”

“…It was clearly shown that as the oxidation proceeds under controlled temperature, Ti atoms migrate to the MXene surface, forming carbon-supported titania (figure 12(e)). The crystal phase of titania was further investigated by Badawy et al [189]. In dry air, anatase and rutile TiO 2 were formed on Ti 3 C 2 T 2 (T=O, OH) MXene, whereas rock-salt TiO was formed under vacuum.…”

Near‐Atomic‐Scale Perspective on the Oxidation of Ti3C2Tx MXenes: Insights from Atom Probe Tomography

“…[35] Several studies have demonstrated how further oxidation severely destroys the integrity of the MXene structure, thereby limiting its lifetime in service and precluding many useful applications due to a decrease in the properties of interest. [36][37][38][39] Although efforts have been made to understand the details of their evolving chemistry during oxidation, [40,41] some questions are still unanswered, such as the role of non-O surface terminations, intercalants, or impurities from synthesis. Designing MXenes with improved oxidation resistance is therefore extremely challenging, and for this reason the improvement of chemical and temperature stability of MXenes is considered in the community to be one of the research challenges of this decade.…”