Fig. 2

Morphological and structural characterizations and bubble releasing behaviors. a, b FESEM images demonstrating the uniformity of the as-prepared FeCoNi-LDH-NWAs and FeCoNi-HNTAs respectively as a large scale view. The insets of (a, b) are the corresponding magnified FESEM images and scale bars are 500 and 200 nm, respectively. c STEM and EDX elemental mapping spectra exhibiting the hollow nature, uneven tube wall, and uniform distribution of Fe (cyan), Co (red), Ni (green), Mo (pink), S (magenta), O (blue), and N (yellow) elements. d TEM image, e HRTEM image. The lattice fringes with the spacing of 0.27 nm and 0.29 nm are in agreement with the (101) and (222) planes of MoS₂ and (Co,Fe,Ni)₉S₈, respectively. f, g AC-STEM images of 1T’ MoS₂ and (Co,Fe,Ni)₉S₈ in FeCoNi-HNTAs, respectively. The upper image of inset of f displays the Mo clusters with tetragonal symmetry marked by short dash line square in f. The corresponding FFT pattern of (Co,Fe,Ni)₉S₈ is shown as the upper image of inset of g. The lower images of the insets of f, g are the corresponding crystal structures, where yellow, cyan, and blue balls represent S, Mo, and Co (or Fe, Ni) atoms. h, i, j Digital photos demonstrating the bubble releasing behaviors on the surface of FeCoNi-HNTAs, FeCoNi-LDH-NWAs, and bare Ni foam for HER. The insets are the corresponding size distribution statistics of releasing bubbles. Scale bars: a 10 μm; b 2 μm; c 100 nm; d 100 nm; e 5 nm; f, g 2 nm; h, i, j 2 mm