Electrophoretic Deposited Mg Ion Functionalized Graphene Oxide-Based Ultrahighly Sensitive Humidity Sensor

Graphene oxide (GO) is a 2-D material widely known for its use as a humidity-sensitive material due to its hydrophilic nature. We report the ultrahigh relative humidity (RH) sensing properties of a GO-coated interdigital electrode (GO-IDE) capacitive sensor. The GO was coated directly on gold interdigital electrodes (IDE) via electrophoretic deposition (EPD) technique. The GO coating was functionalized with magnesium (Mg) ions during the deposition process by using Mg nitrate as an electrolyte. The deposited GO coating was characterized by field emission scanning electron microscopy (FESEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The quality of the GO films and the hydrophilic nature of the film were confirmed via the characterizations. The sensor was tested at 10%-85% RH and demonstrated an average sensitivity of 283 093 pF/% RH, far exceeding that of similar GO-based capacitive sensors. In particular, the sensitivity was 530 800 pF/%RH for the RH range between 45% and 85%. The GO-IDE RH sensor also exhibited good stability, good repeatability, fast response time (51.9 s), and recovery time (4.6 s). The proposed sensor demonstrates the ultrahigh RH sensing properties of electrophoretic deposited GO and a method to functionalize GO coatings via introduction of specific electrolytes easily.