Researchers engineer defects into 2D materials to boost performance
Scientists have developed a method to deliberately introduce randomly distributed defects into molybdenum-based MXenes, ultra-thin materials used in batteries and catalysts. The technique allows precise control over defect density, potentially unlocking better performance for energy storage and other applications without changing the material's core composition.
Originaltitel: Defect Engineering of Mo-based Mo<sub>2-x</sub>CT<sub>z</sub> MXenes
<p>From the development of bronze to the doping of silicon, the discovery and enhancement of materials have played a critical role in enabling disruptive technologies. With the increasing demand for device miniaturization and sustainability, two-dimensional (2D) nanomaterials have gained significant attention since the discovery of graphene, owing to their unique morphology and size. Among these, MXenes exhibit exceptional structural and chemical diversity, making them promising for various applications, such as energy storage and catalysis. </p><p>Despite substantial progress, optimizing the properties of nanomaterials remains essential for overcoming current technological challenges. One strategy for this optimization is defect engineering, which involves the intentional creation of structural defects, such as vacancies. Currently, MXene properties can be modified by altering their composition (e.g., metal elements and/or surface terminations) and introducing ordered vacancies with fixed defect fractions. This thesis presents an alternative approach: the creation of randomly distributed vacancies and vacancy clusters with tunable defect content. </p><p>Paper I introduces the concept of generating random vacancies in 2D MXenes by incorporating a sacrificial element in the parent MAX phase. Specifically, the Mo2Ga2C MAX phase was alloyed with Cr and etched in an HF solution, removing both Cr and Ga atoms. The resulting Mo2-xCTz MXenes exhibited surface defects and enhanced capacitance values. Paper II further expands this approach, demonstrating that varying the Cr content in the precursor results in MXenes with different defect fractions. The limits of Cr incorporation in the precursor phases were investigated through both simulations and experiments. Additionally, 2D MXenes with varying defect concentrations were synthesized, and electrochemical characterizations indicated that the defect concentration could be optimized for superior performance. </p><p>These findings suggest that this defect engineering strategy provides a viable pathway to control defect concentrations and tune MXene properties. In principle, this approach could be extended to other MAX phases and sacrificial elements, unlocking new possibilities for the development of MXenes with novel and enhanced properties. </p>