Researchers say it may be possible to create small, portable CO2 sensors for scuba divers or mountain climbers using their new energy-efficient design.
A new sensor that measures carbon dioxide (CO2) is much smaller than existing sensors, is easier to assemble, and uses much less energy. The new sensor consists of a recently developed composite material that interacts with CO2 molecules and changes its conductivity depending on the concentration of CO2 in the environment. ETH Zurich scientists created a sensor chip with this material that can measure CO2 concentration based on electrical resistance.
The basis of the composite material is a chain-like macromolecule (polymer) made up of salts called ionic liquids, which are liquid and conductive at room temperature. The name of the polymers is slightly misleading as they are called “poly(ionic liquid)s” or PIL, although they are solid rather than liquid.
Scientists worldwide are currently investigating these PIL for use in different applications, such as batteries and CO2 storage. Research shows that PIL can adsorb CO2. “We asked ourselves if we could exploit this property to obtain information on the concentration of CO2 in the air and thereby develop a new type of gas sensor,” says Christoph Willa, doctoral student at the Laboratory for Multifunctional Materials.
Willa and Dorota Koziej, a team leader in the laboratory, eventually succeeded by mixing the polymers with specific inorganic nanoparticles that also interact with CO2. After producing the composite, they made a surprising discovery. “Separately, neither the polymer nor the nanoparticles conduct electricity,” says Willa. “But when we combined them in a certain ratio, their conductivity increased rapidly.” The scientists were also surprised the conductivity of the composite material at room temperature is CO2-dependent. “Until now, chemoresistive materials have displayed these properties only at a temperature of several hundred degrees Celsius,” explains Koziej. Thus, existing CO2 sensors made from chemoresistive materials had to be heated to a high operating temperature.
With the new composite material, that’s not necessary. They suspect that a chemical change induced by the presence of CO2 occurs at the interface between the nanoparticles and the polymers at the nanometer scale. “We think that CO2 effects the mobility of the charged particles in the material,” says Koziej. With the new sensor, scientists are able to measure CO2 concentration over a wide range—rom a concentration of 0.04 volume percent in the Earth’s atmosphere to 0.25 volume percent.
Existing devices that can detect CO2 measure the optical signal and capitalize 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.”