Electrode with chlorine gas provides high power and energy density
Credit: Wiley

Rechargeable batteries and supercapacitors complement each other and could even be partially replaced. Supercapacitors don't last long enough because they don't have enough density. A new approach for making a supercapacitor is better than the old one. The team that developed it drew inspiration from a lizard that has an air bubble in it's mouth.

buffering for consumption spikes by electronic devices and compensation for short-term power outages are some of the applications for supercapacitors. Modern streetcars and buses are powered by supercapacitors. They are being looked at more and more by the solar energy industry.

Supercapacitors can produce very high currents in a short time and have a high power density. Even though they use low electricity usage, they don't last very long. Electric energy storage needs to have a low weight in order to be modern. The stumbling block for the advancement of supercapacitors is the cost of power density.

The East China University of Science and Technology and the University of Oxford have started to overcome this challenge. A little lizard inspired them. Anolis lizards are able to breathe underwater when they dive to find food. They attach an air bubble to a layer of scales on their head in order to do this. They breathe in and out of this bubble. When it is submerged in a solution of table salt as electrolyte, the new porous carbon material can hold onto a layer of gas. Chlorine is used in the gas.

Supercapacitors usually have charge separation and a redox reaction during charging and discharging. The "exhales" are the electrons that transfer from the chlorine gas to the solution. The chlorine oxidizes back to it's original form, returning the gas to the "inhales" of the electrodes. The team used a variety of analytical methods to show that there was no chlorine gas escaping. The supercapacitor has an extremely high power density because of the rapid mass transfer in the thin layer of gas. Even after thousands of cycles, the capacity is the same.

The High Power and Energy Density Supercapacitors through the Chlorine Respiration Mechanism can be found in the Angewandte Chemie International edition. There is a 10.1002/anie.