Figure 2

SEM images of 3D HPCAs (a,d) HPCAs-0.2-800; (b,e) HPCAs-0.4-800; (c,f) HPCAs-0.8-800; TEM images of HPCAs (g) HPCAs-0.2-800; (h) HPCAs-0.4-800; (i) HPCAs-0.8-800; HRTEM images of HPCAs (j) HPCAs-0.2-800; (k) HPCAs-0.4-800; (l) HPCAs-0.8-800.