An Ammonia Sensor Composed of Polypyrrole Synthesized on Reduced Graphene Oxide by Electropolymerization

Abstract We report an ammonia (NH3) sensor in which a ultrathin polypyrrole (PPy) layer is synthesized on reduced graphene oxide (rGO) by electropolymerization. The PPy/rGO composite is characterized by scanning electron microscopy, secondary ion mass spectrometry, Raman spectroscopy, and X-ray photoelectron spectroscopy. The sensor exhibits an excellent performance in the selective sensing of NH3 at room temperature, having a high, fast, reversible and linear response. These performances are attributed to the synergistic effect of the ultrathin PPy layer and rGO. Specifically, NH3 molecules are adsorbed on the ultrathin PPy layer, electrons transfer from NH3 to the PPy layer, changing the PPy layer resistance. The ultrathin PPy layer over rGO allows NH3 molecules to pass through and react with sp2-bonded carbon atoms, also changing the rGO resistance. Moreover, the rGO sheets are not only a support material for the ultrathin PPy electropolymerization but also provide an efficient pathway for electron transfer, thereby, accelerating the sensor response and recovery. Meanwhile, the ultrathin PPy layer plays an important role in the sensor selectivity and immunity to humidity. Our research indicates that the post-step PPy electropolymerization is very promising for sensor fabrication and compatible with CMOS technology. These make it possible to design and manufacture the PPy/rGO sensors with integrated circuits onto the same Si wafer for different applications. Importantly, the fabrication method of the present sensor is easy and low cost. Therefore it is regarded as being scalable for mass production of NH3 sensors.