Fig. 2: Synthesis and characterization of Ni-CMC aerogel and Ni-CNTs/PC.

a Schematic for the preparation of hierarchical Ni-CNTs/PC. b Schematic for synthesizing Ni-CMC hydrogel through the sol-gel strategy followed by swelling treatment. c Top-view SEM images and d HRTEM image of Ni-CNTs30/PC (the white circle in d refers to the location of the etched Ni particle). e Aberration-corrected HAADF-STEM image of Ni-CNTs. f EDS elemental mappings of C, N, and Ni. g Schematic for the tip-growth mode of Ni-CNTs. h Swelling ratio of Ni-CMC hydrogel and Ni nanoparticles (NPs) size versus swelling time. i The thickness of PC NSs and the length of Ni-CNTs in Ni-CNTs/PC versus growth time. Error bars represent the standard deviation of three independent measurements. Source data are provided as a Source Data file.