High-Performance Impedance Humidity Sensor Based on Au Nanoparticle-Modified Hydroxyl-Rich Graphene Oxide

This study explores the impedance response of hydroxyl-rich graphene oxide (HGO) modified with gold nanoparticles (AuNPs) for humidity sensing applications. The results demonstrate that the incorporation of AuNPs significantly enhances the electrical properties of HGO, improving the sensor's overall performance. The sensor layer structure was systematically examined based on the order of material depositiona topic rarely addressed in the literature. Our findings indicate that the initial deposition of AuNP directly onto the aluminum interdigitated film leads to superior sensing efficiency. The AuNP-modified HGO sensor exhibited a high sensitivity of 0.032 log Z/%RH and response times of approximately 0.2 s, highlighting the paramount synergy between both materials. Both HGO and AuNP/HGO sensors exhibited stable hysteresis behavior, with excellent adsorption response times and satisfactory desorption times, confirming their viability for humidity monitoring. Impedance analysis revealed distinct resistive and capacitive properties, with consistent capacitance across different humidity levels. We propose that proton conduction and ionic diffusion are the primary operating mechanisms, with the latter becoming more pronounced in the presence of AuNP, as evidenced by Warburg impedance behavior in Nyquist plots. Importantly, this study suggests that the sensor's sensitivity is not solely due to water absorption but also enhanced by a reduced Schottky barrier resulting from interactions with adsorbed water molecules, thereby providing a broader perspective on the mechanisms influencing sensor performance. These insights were validated through various sensor preparation methods, including layer inversion during deposition.