Fig. 2. Microstructure analysis of the catalyst-coated diaphragm in comparison with catalyst-coated mesh electrode.

a Representative scanning electron microscope image of the Raney Ni catalyst layer. b High resolution transmission electron microscope image of typical Raney Ni particle in the catalyst-coated diaphragm. c Representative ultra-depth optical microscope image of the catalyst-coated diaphragm with Raney Ni catalyst layer. d, e Typical cross-section scanning electron microscope image (d) and elemental mapping (e) of the catalyst-coated diaphragm. f Pore diameter distributions of Zirfon 220 diaphragm, Raney Ni catalyst and the catalyst-coated diaphragm. The pore volume is normalized to the sample mass of the catalyst-coated diaphragm. g, h Scanning electron microscope images of surface (g) and cross section (h) for the Raney Ni catalyst-coated Ni mesh electrode.