Flexible Room Temperature Ammonia Gas Sensor Based on Low-Temperature Tuning of Functional Groups in Grapheme

Abstract

A flexible room temperature ammonia gas sensor based on reduced graphene oxide (RGO) nanosheets has been fabricated on a transparent sheet using photolithography. The structural, morphological, and chemical properties of RGO sensing layer have been analyzed. The higher binding energy of hydroxyl groups with ammonia is utilized for ammonia adsorption, and the groups are tuned at low temperatures by processing graphene oxide. Charge transfer from ammonia to the hydroxyl groups in the RGO sheets is responsible for high response and selectivity of the sensor toward ammonia. Gas sensing characteristics of the sensor was analyzed at various temperatures and humidity levels. The sensor exhibited a selective response toward ammonia vapors among seven volatile organic compounds. The sensor showed a very high response of 930% toward 400-ppm ammonia at 25 °C and 45% relative humidity (RH) level. A quick response of 31 s and full recovery of the sensor after 500 s were recorded when exposed to 400-ppm ammonia. The operation of the sensor at only 1 V facilitates its usage in low-power applications. The sensor exhibited almost negligible deviation in response in the presence of humidity, making it humidity resistant. The flexibility of the sensor was tested by bending the sensor over the range 0°-120°, where the sensor performance started deteriorating after 90 bending. The sensor showed very high stability when tested for 75 days. Therefore, the RGO-based flexible device shows potential toward future commercial room temperature ammonia gas sensors.