The influence of the electrode material on the sensor characteristics of SnO2 thick film gas sensors

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A chemoresistive SnO2 gas sensor measures the resistance of a sensing layer between electrodes to analyze the ambient atmosphere's chemical composition. Noble metal electrodes not only facilitate resistance measurement but also significantly influence sensing performance. This influence stems from electrical factors, such as the electrode gap affecting grain boundaries, and chemical factors due to catalytic processes at the three-phase boundary: electrode, metal oxide, and ambient atmosphere. Solely measuring sensor resistance captures these influences but lacks insight into their causes and potential applications. This work presents operando measurements on screen-printed thick-film SnO2 sensors on Al2O3 substrates, alongside model systems of SnO2 mixed with micrometric Au and Pt powders. Experiments were conducted in dry and humid air, varying CO, H2, and oxygen concentrations. Techniques employed include DC electrical measurements, catalytic conversion experiments, and DRIFTS measurements. Results indicate that sensors with gold electrodes at lower temperatures enhance oxygen adsorption, increasing reactivity with gases like CO and H2. Conversely, sensors with platinum electrodes exhibit reduced signals at specific temperatures due to direct conversion at the noble metal electrodes.