This title presents a new type of CO2 gassensor, that allows the measurement of CO2 gas with very low effort. The measurement principle is based on two semiconducting materials. One the "receptor" and a "transducer" form a semiconductor junction. Electronic changes in the receptor change the electrical resistance in the transducer and therefor allow the easy electrical measurement. The reactivity and the reaction mechanism is thoroughly studied. In the first part the basics and resistance measurements are presented. A comparison between different mixtures is done. The main part studies the surface chemistry with operando DRIFT spectroscopy. The chemical reactivity of different target gases and background gases is studied toroughly. The electronic properties of Oxycarbonates and the combination of oxycarbonate and tin oxide were studied using operando Kelvin probes measurements. The result is that CO2 alters the electron affinity of the material. Once moisture is present, an additional band bending is visible. The band bending dominated in a humid atmosphere, the work function changes. The electronic connection of oxycarbonate and tin oxide, the work function change of Oxycarbonates can be transferred to the tin oxide. Using the collected data, a basic idea of the operation will be presented by a two-semiconductor materials gas sensor.