Survey of etching techniques to produce Cr₂C MXene from Cr₂AlC

Two-dimensional chromium carbide MXene (Cr₂CTX) is predicted to possess a high hydrogen capacity and antiferromagentism which may be employed in hydrogen storage and spintronic applications. As of the time of the work detailed in this thesis, there have not yet been any reported success synthesis of Cr₂CTX. Herein is a systematic survey of different possible etching conditions to produce Cr₂CTX from Cr₂AlC. Three distinct etching techniques previously used to synthesize MXenes were studied. Wet etchings were conducted using either hydrofluoric acid along with sulfuric and hydrochloric acid or hydrochloric acid with fluoride salts. HF/HCl and KF/HCl were the most promising etchants, producing XRD peaks consistent with MXenes. Importantly, samples produced using the wet etchants often contained both unreacted MAX and degradation products, such as CrO3, demonstrating that chromium and aluminum are being etched at comparable rates, preventing the formation of the desired MXene. Additionally, a molten salt technique using zinc chloride was also studied by varying the time and ratio of reagents. This technique also hold promise with several samples possessing XRD peaks consistent with Cr₂CTX. Additionally, the lack of chromium chlorides and presence of zinc chromite indicate that MXene degradation is due to oxygen in the system rather than the molten salt treatment itself.