Electrochemical Properties of Niobium and Vanadium Carbide MXenes as Determined by Synthesis Conditions and Interlayer Environments

Abstract

Since their discovery in 2011, two-dimensional transition metal carbides and nitrides, known as MXenes, have gained considerable interest because of their extensive surface area, excellent conductivity, and distinctive electrochemical characteristics. Numerous studies demonstrate the exceptional electrochemical performance of MXenes, which can support their potential in various energy storage systems. However, despite the growing research on MXenes, studies on non-Ti based MXenes, like Nb2CTx and V2CTx, still need further exploration. While more than 50 different MXenes have been experimentally synthesized, over 70% of MXene studies continue to focus on the first discovered MXene, Ti3C2Tx.1 Conversely, other MXenes do not have clear synthesis protocols or thorough morphological studies linked to their performance. Research on non-Ti MXenes typically emphasizes their ultimate performance in various applications. Yet, they frequently neglect in-depth analyses of morphology, surface terminal groups, and interlayer environments, such as confined water, which significantly influence their inherent properties. This dissertation aims to understand the chemical and electrochemical properties of non-Ti-based MXenes by exploring how their nanostructure, including morphology, surface terminations, and interactions with intercalated ions and water, impacts their performance in energy storage applications. The first project demonstrated that controlling the synthesis conditions of Nb₂CTₓ MXene significantly affects its morphology, stability, and electrochemical properties. In the second project, cobalt intercalation enhanced the capacity and stability of Nb₂CTₓ MXene in aluminum-ion batteries by improving interlayer spacing, reducing electrostatic repulsion, and introducing a pillaring effect. The final project investigated how intercalated cations influence water behavior within V₂CTₓ MXene layers. The results revealed that when different cations change confined water, it can affect the electrochemical performance of energy storage devices. Overall, these findings offer valuable insights into the fundamental relationships between the nanostructure of MXenes and their electrochemical performance in energy storage applications.