Critical Analysis of MXene Production with In-Situ HF Forming Agents for Sustainable Manufacturing

MXenes are an emerging class of materials considered for many applications, such as sensors, catalysis, energy storage devices. The main obstacle towards their massive implementation is the synthesis requiring the direct use of HF as etching agent. The development of alternative synthetic routes exploiting in-situ forming HF agents is the main strategies to overcome this limitation. In this study four different etching methods based on the use of NH4HF2, NaF-HCl, HBF4, and NaBF4-HCl are compared to produce Ti3C2Tx from Ti3AlC2 towards the application of MXenes in sodium ion batteries. Three of such etching methods have already been reported while one is here presented for the first time. The structural analysis of the obtained products is based on X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) analysis. All the materials have been tested in half-cell configuration vs. Na; the charge/discharge profiles and the C-rate tests are discussed and related to specific structural features. Overall, the results reveal that the MXene obtained using the HBF4 etching agent under mild conditions is comparable both in structure and functional properties to the benchmark material, i. e., the MXene produced using HF at 5 % concentration. Indeed, the MXene synthetized with the HBF4 presents the lowest mean voltage and potential hysteresis and shows the highest first cycle efficiency (69.7 %), overcoming the performance of the MXene produced with 5 % HF (67 %). This study proves the possibility to produce MXene with a more sustainable route.