Cabbage-shaped zinc-cobalt oxide (ZnCo2O4) 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 Co3O4 without sacrificing multi-shelled hollow structure. The synthesized cabbage-shaped ZnCo2O4 exhibited the enhanced formaldehyde sensing capability compared to the Co3O4 counterpart. The sensitivity to 100 ppm formaldehyde for ZnCo2O4-sensors is 7.4 at 180 °C, which is 6.2 times higher than that of Co3O4-sensors. In addition, the ZnCo2O4-sensors also show the fast response/recovery time (9/12 s) compared to Co3O4-sensors (55/63 s). Interestingly, Zn2+ 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 ZnCo2O4-based sensors. The results offer crucial insights in realization of highly sensitive spinel oxide materials for CSs.