Fluoride-Free Synthesis of Two-Dimensional Titanium Carbide (MXene)

MXenes are a fascinating class of two-dimensional (2D) materials that consist of few atoms thick layers of transition metal carbides, nitrides or carbonitrides. They have aroused increasing attention due to their unique combination of hydrophilic properties and good electrical conductivity. The production of MXene relies on chemical etching of aluminium (Al) layers from titanium aluminium carbide (Ti3AlC2, a MAX phase). Although diverse etching conditions have been identified, the state-of-the-art strategies require the handling of hydrofluoric acid or fluoride-based compounds, which result in highly toxic and corrosive liquid waste, and the functionalization of Ti3C2 surfaces with fluorine- and oxygen-containing terminations. Along with the considerable safety issues, fluoridated etchants have negative impact on the specific capacitance of etched materials when used as electrodes for supercapacitors. 

To address these problems, researchers from Technical University of Dresden (Chair for Molecular Functional Materials) and collaborators have developed an efficient electrochemical strategy to prepare Ti3C2Tx (T=O, OH) (MXene) in a binary aqueous system. The anodic etching of Al atoms followed by the replacement with hydroxide groups enable the formation of single or bilayer sheets with high yield (>90 %) and large average dimension. The results are comparable or even better than those made from classic etching techniques using HF or LiF/HCl. For the use as energy storage materials, all-solid-state supercapacitors assembled with Ti3C2Tx films deliver a high areal capacitance of 220 mF cm-2 (scan rate: 10 mV s-1). More importantly, this method does not require any dangerous fluoride-containing agents or harsh etching conditions, therefore it is appealing for the practical production of novel MXene materials. 

This work was financially supported by the Deutsche Forschungsgemeinschaft (MX-OSMOPED project), ERC grants on 2DMATER, Graphene Core 2 and EC under Graphene Flagship (NO. CNECT-ICT-604391) and Center for Advancing Electronics Dresden (cfaed). 

Reference: Sheng Yang, Panpan Zhang, Faxing Wang, Antonio Gaetano Ricciardulli, Martin R. Lohe, Paul W. M. Blom & Xinliang Feng*, Fluoride-Free Synthesis of Two-Dimensional Titanium Carbide (MXene) Using A Binary Aqueous System. Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201809662 

Angewandte Chemie