For the powdered carbon, film electrodes were used for making electrochemical cells (film-making method stated above), while for activated carbon cloths, the cloths were directly used as electrodes. All the coin cells were two-electrode cells, and were assembled in a N2-filled glovebox. The coin cells were symmetric (i.e., both electrodes were the same carbon material). The electrodes were cut using a stainless-steel manual punching cutter (diameter "5/16" inch, Hilka Tools), and the two electrodes in each cell had identical masses within 0.2 mg. Two electrodes were placed onto a coin cell bottom casing with a larger diameter ("9/16" inch) glass fibre separator placed between the electrodes. Around 150 µL of electrolyte was added around the separator with a Pasteur pipette. After the electrolyte fully wetted the electrodes, two SS316 spacing disks and one SS316 spring were placed on top of the electrodes. The top casing was then used to close the coin cell. The coin cells were sealed with a Compact Hydraulic Coin Cell Crimper (Cambridge Energy Solutions). All coin cells parts were supplied by Cambridge Energy Solutions.