A new CO2 sensor developed by Swiss researchers

Salt-based CO2 sensor could help better protect divers

An innovative CO2 sensor based on polymers consisting of a type of salt could help monitor air-quality for scuba divers or mountaineers.

The device, developed by researchers from the Max Planck Institute and the ETH Zurich, is much smaller than any existing CO2 sensor. It also requires less energy and is simpler overall.

The sensitive part of the device is made of a polymer nano-particle composite containing a special type of salts called the ionic liquids. These salts are conductive at room temperature and change their conductivity when interacting with CO2. The higher the concentration of the CO2 in the surrounding atmosphere, the more significant the change in conductivity.

By depositing the polymer on a chip, the researchers were able to determine the CO2 concentration by measuring electrical resistance.

"Until now, chemoresistive materials have displayed these properties only at a temperature of several hundred degrees Celsius," said Dorota Koziej, a leader of the research team at ETH Zurich. “Existing CO2 sensors made from chemoresistive materials had to be heated to a high operating temperature.”

The polymer, also known as the polyionic liquid (PIL), is currently an object of intense interest of the scientific community. Previously, engineers tried to build batteries or CO2 storage devices using the material. The ability of the material to react with CO2 was known, but not the exact principle behind this reaction.

With the new sensor, scientists are able to measure CO2 concentration over a wide range, from a concentration of 0.04 volume per cent in the Earth's atmosphere to 0.25 volume per cent.

Existing devices that can detect CO2 measure the optical signal and capitalise on the fact that CO2 absorbs infrared light. In comparison, researchers believe that with the new material much smaller, portable devices can be developed that will require less energy. According to Koziej, "portable devices to measure breathing air for scuba diving, extreme altitude mountaineering or medical applications are now conceivable".

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