MXene Templated assembly of hierarchical Al/CuO/V2C nanothermite with excellent energy release efficiency and highly tunable performance

Introduction

Nanothermite is a new class of energetic materials that has emerged as a result of advancements in nanotechnology. It is widely used in igniters, thrusters, and ammunition^{1, 2–3}. Nanothermite combines thermite with nanotechnology, using nanoparticles instead of conventional micro- or larger-sized particles for both oxidizers and aluminum. The primary advantage of this approach is the enhanced energy release rate of the thermite reaction. This improvement arises from the increased surface-to-volume ratio, which enhances reactivity^{4, 5–6}. However, the large surface area of nano-sized aluminum and oxidizers introduces additional surface energy. This leads to spontaneous nanoparticle agglomeration as a way to reduce energy, which significantly impairs the energy release efficiency of nanothermite^7,8.

Significant efforts have been made to reduce the agglomeration of nano Al and oxidizer particles, aiming for a more even mixing between Al and oxidizer. These methods can be classified into two types based on whether additives are used. For additive-free approaches, top-down micromachining methods are typically employed during fabrication, such as magnetic sputtering^9,10, E-beam evaporation^11,12, electrospray¹³, and electrospinning¹⁴. These techniques achieve homogeneity through multilayer or core-shell structures and are compatible with integrated circuits (IC) and microelectromechanical systems (MEMS) manufacturing, potentially integrating into chips. However, these methods often introduce alumina passivation layers at Al/oxidizer interfaces in air, which can hinder the reaction process. In addition, they consume significant energy and time¹⁵. For methods that include additives, a bottom-up strategy is preferred, where the additive acts as a binding agent between Al and oxidizer to build desired nanothermite structures through self-assembly¹⁶, such as core-shell⁵ and nanocomposite¹⁷ configurations. These additives effectively reduce nanoparticle agglomeration by preventing adhesion, thereby increasing contact between Al and the oxidizer. Nevertheless, additives often have minimal impact on the thermite reaction while impeding oxygen diffusion. This structural advantage is counteracted by these limitations.

As summarized above, while numerous efforts have been made, both top-down and bottom-up approaches continue to struggle with reducing nanoparticle agglomeration without compromising the energy release efficiency of thermite reactions. To address this challenge, we propose a strategy of fabricating hierarchical nanothermite through the ordered self-assembly of Al and oxidizer nanoparticles, utilizing single-layer MXene as a template. MXenes have...