Humidity sensing properties of reduced humic acid

Humidity sensors are utilized as part of the control system in all air conditioning equipment in the world. These important sensors can be divided into three main types including capacitive, resistance, and thermal conductivity. Of these the resistive type are the most cost effective, smallest in size, best interchangeability in the field, and long term stability. For the first time, we report the use of reduced humic acid as a resistive humidity sensor (RH 12.4% up to 97.1%). This material is promising due to the low cost, high sensitivity and environmentally friendliness. Moreover, this material has a fast response and recovery time compared to the graphene oxide. In contrast to graphene oxide it was found that the resistance of the sensor decreases as the relative humidity increases. Humidity sensing mechanism of the reduced humic acid sensor has been discussed.