Sensing mechanism of room temperature CO2 sensors based on primary amino groups

This work reports measurements to elucidate the reaction mechanisms of sensitive materials containing primary amino groups with CO2. The sensing mechanism is based on their ability to perform reversible acid–base reactions. The effect discussed for most of the previously used sensing layers concerns the formation of bicarbonate species, which requires H2O as well as an increased temperature. By using work function readout technology an operation at room temperature of the sensing layers is enabled providing satisfying sensor responses in terms of SNR (signal noise ratio) and response time. In contrast to the previously investigated higher operation temperature, the response resulting from a room temperature measurement appears to be dominated by the reversible formation of carbamate, which does not require the presence of water. The presence of carbamate is considered to be the reason of the improved sensing performance of this sensing material at room temperature with work function readout.To confirm this hypothesis, DRIFT-MIR, Raman, XPS and NMR spectroscopy were employed to investigate the formation of species after manufacturing of the sensitive layers. Besides the formation of bicarbonate, the results show a strong indication for carbamate formation.