AbstractA potentiometric thin‐film sensor to detect CO₂ in a wide range (2–100 %) has been developed. The system has been fabricated depositing a reference electrode of Pt, a solid electrolyte of YSZ (Yttria‐stabilized Zirconia), a sensing phase made of Li₂CO₃ and a working electrode of Au via Physical Vapor Deposition (PVD). Characterization of the different elements has provided the optimal fabrication parameters and the system response for CO₂ concentrations can be measured from 2 to 100 % at 450 °C. The sensor behaves as a non‐Nerstian system and slightly deviates from a linear response with the logarithm of CO₂ until the CO₂ concentration reaches the 30 %. Higher CO₂ amounts make the response divert more from the Nernst law but give a stable and reproducible response to CO₂ in a wide range of concentrations. Based on these promising results the recovery time, stability, repeatability and selectivity of the sensor have been measured. The performance showed by the thin film sensor proves the feasibility of the use of this system for biogas and natural gas applications owing to its very good consistency at low temperature in a wide concentration range.