Carbon capture, storage, and utilization have become familiar terms when discussing climate change mitigation actions. Such endeavors demand the availability of smart and inexpensive devices for CO2 monitoring. To date, CO2 detection relies on optical properties and there is a lack of devices based on solid-state gas sensors, which can be miniaturized and easily made compatible with Internet of Things platforms. With this purpose, we present an innovative semiconductor as a functional material for CO2 detection. A nanostructured In2O3 film, functionalized by Na, proves to enhance the surface reactivity of pristine oxide and promote the chemisorption of even rather an inert molecule as CO2. An advanced operando equipment based on surface-sensitive diffuse infrared Fourier transform is used to investigate its improved surface reactivity. The role of sodium is to increase the concentration of active sites such as oxygen vacancies and, in turn, to strengthen CO2 adsorption and reaction at the surface. It results in a change in film conductivity, i.e., in transduction of a concentration of CO2. The films exhibit excellent sensitivity and selectivity to CO2 over an extra-wide range of concentrations (250-5000 ppm), which covers most indoor and outdoor applications due to the marginal influence by environmental humidity.
Keywords: CO2 detection; In2O3; chemically active metal oxides; operando spectroscopies; smart sensors for IoT.