Hydrothermal synthesis of metal carbide-derived metal oxide nanoparticles for electrochemical energy storage (electro-MOXen)

• Applicant: Professor Dr. Volker Presser
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398028893

This project focuses on the development of metal carbide-derived metal oxide nanoparticles for electrochemical applications. Depending on the synthesis parameters, metal oxide particles or nanohybrids with residual carbide or carbon component will be obtained. The synthesis starts with the production of a ternary metal carbide (MAX phase), which can be delaminated to two-dimensional carbides (MXenes). The latter can be (fully) oxidized to metal oxide nanoparticles or (partially) oxidized to form a metal oxide / carbide (or carbon) hybrids. MAX-phases belong to a large group of laminated, ternary metal carbides, carbonitrides, and nitrides with the chemical composition Mn+1AXn. M is a transition metal, A an element of group 13 and 14 and X carbon or nitrogen. The M-layers are connected by the A-atoms and the X-atoms fill the gap of the M-octahedra. Selective etching of A-atoms HF treatment yields two-dimensional metal carbides (M-X layers). This material is called MXene and displays interesting mechanical, electrical and electrochemical properties. Subsequent oxidation of the delaminated MXenes forms metal oxide nanoparticles or hybrids with carbon or carbide dependent on the synthesis conditions.Different types of MAX phases were already synthesized by us including Ti3AlC2 und Ti3SiC2. Using chemical treatment, etching of A-atoms is achieved, resulting in layered metal carbides (MXenes). In preliminary work, we have demonstrated adjusted oxidation of Ti3C2 (MXen) to form TiO2-layers (MOXen) using short-term thermal annealing in synthetic air at high temperatures. However, there are still several unresolved issues to achieve high purity and reproducible MOXenes for usage in batteries or supercapacitors. In this project, MOXenes and their hybrids with carbon or carbide will be developed using 211-MAX-phases. We will vary the M-atom (V2AlC, Ti2AlC, Nb2AlC) and also investigate MAX-phases with mixed M-atom occupancy ((Ti,Nb)2AlC, (Ti,V)2AlC). The delamination of MAX to MXene will be exclusively performed by HF treatment and the calcination to metal oxide by using hydrothermal reactions. Dependent on the synthesis conditions, pure metal oxide nanoparticles can be generated or metal oxide / carbide (or carbon) nanohybrids. The latter hybrids are especially interesting for electrochemical applications due to their high intrinsic electrical conductivity in addition to the electrochemically active material (metal oxide). Rigorous electrochemical benchmarking will be carried out for all MOXene materials. All electrochemical measurements will be performed in asymmetric hybrid cells using organic electrolyte. The characterization focuses on lithium and sodium intercalation with state-of-the-art characterization techniques to investigate the specific energy, power, and performance stability. In situ methods will complement our mechanistic understanding of the energy storage processes.

• DFG Programme: Research Grants