Sensing Properties of Pd-Loaded Co(3)O(4) Film for a ppb-Level NO Gas Sensor

We prepared 0.1 wt%–30 wt% Pd-loaded Co(3)O(4) by a colloidal mixing method and investigated the sensing properties of a Pd-loaded Co(3)O(4) sensor element, such as the sensor response, 90% response time, 90% recovery time, and signal-to-noise (S/N) ratio, toward low nitric oxide (NO) gas levels in the range from 50 to 200 parts per billion. The structural properties of the Pd-loaded Co(3)O(4) powder were investigated using X-ray diffraction analysis and transmission electron microscopy. Pd in the powder existed as PdO. The sensor elements with 0.1 wt%–10 wt% Pd content have higher sensor properties than those without any Pd content. The response of the sensor element with a 30 wt% Pd content decreased markedly because of the aggregation and poor dispersibility of the PdO particles. High sensor response and S/N ratio toward the NO gas were achieved when a sensor element with 10 wt% Pd content was used.