The fabrication of Ti3C2 and Ti3CN MXenes by electrochemical etching

2D MXenes are well-known for their outstanding performance in electrochemical energy storage and many other applications owing to their high conductivity and specific surface area. An obstacle to the wider synthesis of MXenes for research and industrial applications is the use of hazardous hydrofluoric acid (HF) during their synthesis. Herein, we developed the electrochemical etching process for the synthesis of Ti3C2 and Ti3CN MXenes by using aqueous tetrafluoroboric acid as the electrolyte, thus only involving a very low concentration of HF. The effect of electrical potential and temperature on the etching rate is studied and compared to chemical etching with HBF4. A mechanism based on the selective anodic dissolution of aluminium from Ti3AlC2 and Ti3AlCN with the tetrafluoroborate ion is proposed. The MXene formation was confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and electron microscopy. The MXene flakes from the electrochemical etching process have larger lateral dimensions compared to chemically etched MXene flakes as a result of the suppression of the HF decomposition and rapid etching rate. The electrodes of lithium-ion supercapacitors made from electrochemically etched Ti3C2 and Ti3CN exhibited cycle performance and rate capabilities comparable to HF-etched MXenes.