Fig. 1.

Top-down vs bottom-up infilling. a The top-down infilling method. Left to right: sol is casted onto a porous electrode; sol above the porous electrode gels forming a skin; sol in the porous electrode gels, leaving behind voids; a free-standing incompletely filled electrode is obtained after the separation from the substrate. b The bottom-up infilling method. Left to right: sol is cast on a porous electrode located on a gas-permeable substrate and covered with an impermeable film; the gel forms from the bottom-up until the entire porous electrode is infilled with gel; a free-standing gel-filled electrode is obtained after removal of the substrate. c SEM images of the top of the MWCNT electrodes infilled with gel electrolyte by the top-down (left) and bottom-up (right) methods. Overlaid on the images are energy dispersive spectroscopy scans where the phosphorus peaks indicate the presence of the electrolyte. Scale bar for c is 200 nm