Bimetallic Au@Pt Nanocatalysts for Gas Sensors

Abstract

Recently, gas sensors have been extensively investigated to improve their sensitivity and selectivity, especially for industrial workplaces with various hazardous gases. Among them, wearable gas sensors are emerging for continuous monitoring of hazardous gases. Metal oxide semiconductors (MOSs) are commonly employed as sensing materials and classified as n-type or p-type according to the majority charge carrier. Remarkably, due to their distinct conduction paths, p-type MOSs exhibit lower sensitivity compared to n-type MOSs, however, this characteristic can be a significant advantage for the sensor, allowing it to operate at a low voltage. Accordingly, after an introduction to gas sensors and metal oxides semiconductors (MOSs), this work investigates bimetallic nanoparticles, specifically focusing on their role as nanocatalysts (NCs) in gas sensors. The goal is to enhance the performance of p-type MOSs by increasing reaction sites and controlling adsorption strength to oxygen and gas analytes. In Part II, bimetallic Au@Pt NCs were synthesized, characterized, and applied to the surface of p-type NiO nanohelices (NHs) to enhance their performance as gas sensors. The coating condition was optimized for the uniform decoration of Au@Pt NCs onto the NiO NHs sensors. The electronic and chemical sensitization of Au@Pt NCs was confirmed by observing lattice planes involved in the oxygen adsorption process and XPS analysis to demonstrate the enhancement in the electronic properties of the sensor surface. As a result, Au@Pt NCs on NiO NHs sensor exhibited enhanced sensitivity and selectivity toward 10 ppm NO2 at 200 ℃ compared to bare NiO NHs. In addition, the gas sensor showed excellent long-term stability by maintaining its sensitivity to NO2 even after a month. The notable improvement in sensing performance might be attributed to the significant increase in catalytic activity by Au@Pt NCs. In summary, my M.S. thesis research, introducing bimetallic NCs onto p-type NiO NHs, would provide a new strategy to overcome the inherent limitations of p-type gas sensor, thereby promising enhanced sensor performance. Furthermore, the gas sensor employing p-type NiO NHs with Au@Pt NCs would be successfully harnessed for practical applications in air pollution monitoring.