Fig. 1

a Elements in MAX phases and MXenes. b Atomic structures of different MAX phases. Scanning electron microscopy (SEM) images of c a Ti₃AlC₂ particle and d accordion-like multilayer structure of Ti₃C₂T_x MXene after removal of the Al atoms from Ti₃AlC₂ by HF etching. e Exfoliated single-layer Ti₃C₂T_x MXene sheet on an anodized aluminum oxide disk. HAADF-STEM images from single-layer Ti₃C₂T_x MXene flakes prepared using: f 2.7 wt% HF, g 5.3 wt % HF, and h 7 wt % HF. i Scatter plot of defect concentrations from images acquired from samples produced using different HF acid concentrations. The red line shows the error plot with the average and standard deviation for different HF acid concentrations. j V_Ti formation energy on bare Ti₃C₂ and terminated single-layer Ti₃C₂T_x. k Formation energy of \({V}_{Ti}^{C}\) clusters as a function of number of V_Ti. b Reproduced with permissions from ref. [7]. Copyright (2020), Elsevier. c, d Reproduced with permissions from ref. [8], Copyright (2012), American Chemical Society. e Reproduced with permissions from ref. [12]. Copyright (2016), American Association for the advancement of Science, Science. f–k Reproduced with permissions from ref. [32]. Copyright (2016). American Chemical Society