A practical carbon dioxide gas sensor using room-temperature hydrogen plasma reduced graphene oxide

We report on the development of a carbon dioxide gas sensor from the room-temperature reduction of graphene oxide via hydrogen plasma. The hydrogen plasma contains radicals and atoms which give dissociation energies for oxygen functional groups, which is capable of reducing the graphene oxide. The sample morphology, degree of reduction, chemical bonding and gas sensing capability were systematically studied. The effective removal of oxygen functional groups at the edges and both basal planes while restoring C=C bonds has been observed by AFM, XPS and Raman analysis. The C/O ratio increased from 0.81 to 7.9 and the resistance decreased significantly from 33 kΩ to 1.6 kΩ after the reduction process. The fabricated rGO-F20 sensor shows the highest CO2 gas sensing response of 71% and 15% at 1500 ppm in N2 (37% RH) and air environment (68% RH), respectively. In addition, the sensor shows a good repeatability performance with the sensing and recovery time of about 4 min when exposed to 750 and 769 ppm CO2 concentration. The repeatability performance was measured in air environment at 68% RH without external assisted recovery. This simple, room-temperature reduction process and sensing capability, low cost fabrication process of a graphene sensor could lead to the implementation of a practical indoor air quality monitor.