High performance gas sensors based on layered cobaltite nanoflakes with moisture resistance

Metal oxide semiconductor have been widely used as sensing materials for detecting various gases with trace concentrations. However, the sensing properties of layered cobaltites with metallic conductivity have not been investigated to date. In this work, we developed a convenient preparation method of NaxCoO2 nanoflakes via aqueous ultrasonic exfoliation of NaxCoO2 single crystals. The sensor based on NaxCoO2 nanoflakes was fabricated, whose resistance is obviously smaller than that of the typical metal oxide based sensors. It shows less response to n-hexane, toluene, xylene, ammonia, methanol, ethanol and acetone. However, it exhibits excellent sensing performance to n-butanol and good moisture-resistance, and the sensitivity to 50 ppm n-butanol is up to 4.48 with the response time of 95 s and the recovery time of 154 s at the optimum working temperature of 200 °C. Owning to the high electric conductivity of NaxCoO2 layers, the sensor presents a very low noise and a high signal-to-noise ratio value with the detection limit at ppb level. The layered cobaltites exhibit the rich phase diagram and the nanoflakes are versatile surface functionalization. This work provides insight for layered cobaltites to be employed as highly sensitive sensors.