The anodic polarization of the MAX phase triggers the dissolution of aluminum accompanied by the release of BF3 gas, whilst a proton is reduced to hydrogen gas on the surface of the cathode. Note that +1 V was applied to all electrochemical etching to minimize the oxidation of the MXene. The initial concentration of HBF4 in both electrochemical and chemical etching was 24 %. MAX phases to MXene, the time required for the complete etching with HBF4 in the absence of voltage at 35 °C was 60 hours (Figure ). Note that for some MXene samples, two (002) peaks were observed due to the different amounts of water and ions intercalated between the MXene layers. Figure shows the amperometry of electrochemical etching carried out at 35 °C, 45 °C and 50 °C, respectively. In general, a correlation between the aluminium content in the MAX phases with the etching current can be seen. Initially, a high current is always observed; this is due to the anodic dissolution of aluminium oxide impurities mixed with the MAX phase precursor. After that, the current becomes stable and gradually decreases as the etching time increases. This is because of the decrease of aluminium content in the MAX phases as etching time increases. Furthermore, the drop in etching current may be attributed to the fact that the anodic dissolution of the aluminium closer to the surface occurs at a faster rate than the aluminium in the core of the crystal. When the etching is completed, the current will soon reach a plateau, as all the aluminum in the MAX phase is consumed by the anodic dissolution. At this stage, the current flow detected is mainly contributed to the introduction of surface terminations, as a higher amount of O and F content is detected for over-etched MXene (further discussed in XPS section). The presence of this current plateau is also an indication that both Ti3C2 and Ti3CN are stable and have a slow oxidation rate at the applied condition.