Cabbage-shaped zinc-cobalt oxide (ZnCoO) sensing materials: Effects of zinc ion substitution and enhanced formaldehyde sensing properties.

Exploiting chemical sensors (CSs) with high-activity sensitive materials is very important for the detection of volatile organic compounds (VOCs). Co-containing spinel oxides are potential candidates for sensing layers. However, the intrinsic activity always hinders their further progress of sensing performances such as sensitivity and selectivity. Here, a facile strategy is successfully developed for the substitution of Co cations into Zn cations in CoO without sacrificing multi-shelled hollow structure. The synthesized cabbage-shaped ZnCoO exhibited the enhanced formaldehyde sensing capability compared to the CoO counterpart. The sensitivity to 100 ppm formaldehyde for ZnCoO-sensors is 7.4 at 180 °C, which is 6.2 times higher than that of CoO-sensors. In addition, the ZnCoO-sensors also show the fast response/recovery time (9/12 s) compared to CoO-sensors (55/63 s). Interestingly, Zn introduction can facilitate the accumulation of holes and generate more defective oxygen and adsorbed oxygen effectively. Consequently, remarkably improved sensitivity, selectively and fast response/recovery process are demonstrated for the ZnCoO-based sensors. The results offer crucial insights in realization of highly sensitive spinel oxide materials for CSs.