Effect of zinc : cobalt composition in ZnCo2O4 spinels for highly selective liquefied petroleum gas sensing at low and high temperatures

Nano ZnCo2O4 mixed phase materials were synthesized at varying zinc and cobalt ratios such as 1 : 1, 1 : 1.5, 1 : 2, 1 : 2.5 and 1 : 3. With a change in composition from 1 : 1 to 1 : 2.5, the gas sensing response characteristics increased two times (from 40 to 77.5 kU), while at higher zinc cobalt composition (1 : 3) a saturation point is shown (about 80 kU). This shows that optimal cobalt loading (1 : 2.5) leads to a two times enhancement in redox ability (from 174 to 346 mmol) and number of active sites, and this upshot significantly helps the sensing response reach a much lower 10 ppm and increases the saturation point to a higher 60 ppm LPG concentration. Furthermore, nano ZnCo2O4 (with a zinc and cobalt ratio of 1 : 2.5) material exhibited an excellent response time (similar to 80-90 s), rapid recovery time (similar to 65-75 s), excellent repeatability (fourth cycle), good selectivity (for LPG), higher gas response (similar to 77.5 k Omega), lower as well as higher operating temperature (from 30 to 250 degrees C). The results clearly reveal that by tuning cobalt composition in ZnxCo(2-x)O(4), we can achieve maximum sensing efficiency and repeatability.