A Pioneering Tactic to Design and Develop Highly Sensitive and Selective Gas Sensors—Exsolution Catalyst

The gas sensing characteristics of oxide semiconductors can be enhanced or modified by loading noble metal or metal oxide catalysts. The uniform distribution of nanoscale catalysts with high thermal stability over the sensing materials is essential for the sensors operated at elevated temperatures. An<i> in situ</i> exsolution process provides a facile synthetic route to form second-phase nanoparticles with uniform distribution, excellent thermochemical stability, and strong adhesion on the mother phase, which can be applied to various applications such as catalysts, batteries, and sensors. Herein, the effect of Co-exsolved nanoparticles on gas sensing characteristics of La_0.43Ca_0.37Co_0.06Ti_0.94O_3-d (LCCoT) was investigated. Depending on the reduction temperature of the exsolution process, the amount and size of Co-exsolved nanoparticles on the surface of the perovskite mother-phase can be adjusted. The LCCoT with Co-exsolved nanoparticles prepared by the reduction at 700 ^oC exhibited the response (resistance ratio) of 116.3 to 5 ppm ethanol at 350 ^oC, which is 10-fold higher than the response of the sensor without exsolution. The high gas response is attributed to the catalytic effect promoted by uniformly distributed Co-exsolved nanoparticles as well as the formation of p-n junctions on the sensing surface during the reduction. We demonstrate that the catalytic effect of Co-exsolved nanoparticles using a proton transfer reaction-quadrupole mass spectrometer (PTR-QMS). The control of the amount and distribution of exsolved nanoparticles on semiconductor chemiresistors provides a new pathway to design high-performance gas sensors with enhanced thermal stability.