Synthesis of Nb-MXenes for Electrocatalysis Applications

Abstract

MXene is the newest class of 2D materials composed of carbides, nitrides and carbonitrides of transition metals. They are promising materials for electrochemical energy storage and in the field of electrocatalysis 1 . This work proposes the synthesis of Nb-MXene from MAX phase precursor and its characterization regarding morphology, structure and electrochemical activity. First, the precursor MAX phase of niobium was produced by mixing Nb, Al and NbC in powder and the reaction process in a tubular furnace, argon atmosphere, at 1640°C, for 3 h. Subsequently, the chemical synthesis was performed at 60 °C, 96 h, by LiF+HCl (1:10 w/w) + 1g of MAX phase, centrifuged and washed with DI water until pH~6 and dried in a vacuum oven. SEM images (Fig. 1 left) confirmed the morphology 2,3 typical of the MAX phase and the effective process of chemical synthesis. The etching process occurred indicating success in the exfoliation, separating the layers forming multilayer MXenes (Fig. 1, right side) 2 . A mixture of Nb 4 AlC 3 and Nb 2 AlC was obtained in the MAX phase. Successful synthesis of MXene is confirmed by shift of the diffraction peaks corresponding to the reflection from (002) plane from 7.36° and 12.75° in case of MAX phase to 5.28°, indicating the removal of Al from the structure 2 (Fig. 2). MXene in a form of a thin film on a conductive substrate was tested for oxygen reduction reaction (ORR) in 3 M KOH electrolyte. Fig. 3 shows a clear increase of current density in O 2 -saturated solution corresponding to O 2 reduction. The peak was visible at 0.7 V with peak current density reaching 0.53 mAcm -2 . This supports further exploration of MXene as an electrocatalyst for ORR, including tolerance and stability tests. References 1- C. Zhan, M. Naguib, M. Lukatskaya, P. R. C. Kent, Y. Gogotsi, D. Jiang. Understanding the MXene Pseudocapacitance, J. Phys. Chem. Lett, 9 (2018) 1223−1228. DOI: 10.1021/acs.jpclett.8b00200 2- Y. Tan, Z. Zhu, X. Zhang, J. Zhang, Y. Zhou, H. Li, H. Qin, Y. Bo, Z. Pan, Nb4C3Tx (MXene) as a new stable catalyst for the hydrogen evolution reaction, International Journal of Hydrogen Energy, 46 (2021) 1955-1966. DOI: 10.1016/j.ijhydene.2020.10.046. 3- M. Shekhirev, C. E. Shuck, A. Sarycheva, Y. Gogotsi, Characterization of MXenes at every step, from their precursors to single flakes and assembled films, Progress in Materials Science, 120 (2021) 100757 https://doi.org/10.1016/j.pmatsci.2020.100757. Figure 1