Fig. 3: Microstructural characteristics and functionalities of the 3D-printed materials.

a, b HRSEM images of printed Au nanocrystals. TEM (c) and HRTEM (d) images of printed Au nanocrystals. Inset in the (d): electron diffraction pattern. e XRD patterns of as-synthesised Au and printed Au nanocrystals. f N₂ physisorption isotherms of printed Au sample at 77 K. Inset: pore size distribution derived from Barrett-Joyner-Halenda (BJH) analysis. g Summarised specific surface areas and silica equivalents of printed inorganic porous materials. h Magnetic hysteresis loops of as-synthesised Fe₃O₄ (black) and printed nanocrystals (red) measured at 2 K and 300 K. i UV-Vis absorption and PL spectrum of CdSe nanocrystals (black) and printed wet (blue), and dried (red) samples. j Electrical conductivities of printed Au porous sample, xerogel, and sintered sample. k ORR polarisation curves of FePt nanocrystal building blocks, Pt/C, FePt/C, and electrochemically activated, HCl-treated, printed FePt nanocrystals (treated printed FePt). The catalyst loading amounts were optimised at 20 μg_Pt cm^–2 for Pt/C and FePt/C and at 50 μg_Pt cm^–2 for treated printed FePt. l ECSA vs. MA_{0.9 V} plot for the comparison of this work with the previous literatures of Pt-based self-supported ORR catalysts. US Department of Energy (DOE) technical target for ORR MA_{0.9 V} (0.44 A mg_Pt^–1) are presented as yellow line. m MA_{0.9 V} values before and after the 10,000 cycles of ORR accelerated durability test (ADT) in 0.1 M HClO₄.