Low Cost, Flexible, Room Temperature Gas Sensor: Polypyrrole-Modified Laser-Induced Graphene for Ammonia Detection

Air quality monitoring is essential to measure and detect gases to identify potential risks to public health and ensure safety. The colorless, pungent-smelling, suffocating Ammonia (NH₃) ranks among the top gases of interest due to its hazardous nature. The three principal sources of ammonia in the environment are the natural phenomena of nitrification and ammonification, resulting from the nitrogen cycle (agriculture and livestock) and combustion from motor vehicles and industries.

Developing a flexible NH₃ sensor that is light, thin, and can work on any surface is ideal for wearable devices and Internet of Things (IoT) applications. This flexible sensor can be used in various ways by integrating them into the clothing of the chemical industry and farm workers on animals in animal farms.

Experimenting with features like sensitive materials, structures, and fabrication methods, researchers have developed various NH₃ sensors, including optical, electrochemical, and chemoresistive sensors. Chemoresistive sensors have an edge due to their advantages and characteristics, such as ease of fabrication, high sensitivity, quick response, low cost, and simple operation.

Among chemoresistive sensors, laser-induced graphene (LIG) sensors have attracted the attention of researchers due to their unique properties and simple laser fabrication process. With good mechanical flexibility, it also exhibits excellent porosity and electrical conductivity, high thermal stability, and electrochemical performance, and with chemical modification, it holds the potential for selective gas detection.

This study explores the electrochemical synthesis of polypyrrole (PPy) on laser-induced graphene (LIG) electrodes for gas sensing. The researchers present a simple, low-cost method to produce PPy@LIG nanocomposites (NCs), which are used to create flexible sensors for detecting ammonia (NH₃) at room temperature.

Traditional ammonia sensors often require high operational temperatures, leading to high power consumption and reduced durability. The sensor described here operates at room temperature, making it more energy-efficient and suitable for real-time environmental monitoring.

The PPy@LIG sensor's fabrication involves a two-step process. First, laser-induced graphene (LIG) is synthesized on a polyimide film using a CO₂ laser. The resulting porous LIG structure provides a large surface area for gas interaction. In the second step, polypyrrole is electrochemically synthesized on the LIG electrodes, forming the PPy@LIG nanocomposite. This novel approach enhances the sensor's sensitivity to ammonia by leveraging the unique properties of both LIG and PPy.

The performance of the sensor was evaluated by exposing them to different concentrations of ammonia gas at room temperature. The PPy@LIG sensors show 14 times higher sensitivity than pure LIG, excellent repeatability, and a low detection limit of 1 ppm. The sensor exhibited excellent repeatability, stability over time, and selectivity towards ammonia over other gases, even in humid conditions.

The flexible and cost-effective gas sensors developed using PPy@LIG nanocomposites showed significant potential in ammonia gas detection. The unique properties, like high sensitivity, repeatability, and a low detection limit, make it a promising candidate for advanced gas-sensing systems. The work presented here will contribute to the advancement of ammonia gas sensors for potential applications in environmental monitoring and to improve air quality monitoring.