Air pollution is now considered to be the world’s largest environmental health threat, accounting for 7 million deaths around the world every year. Air pollution causes and exacerbates a number of diseases, ranging from asthma to cancer, pulmonary illnesses and heart disease. To this end, the development of robust, efficient and cost-effective infrastructure for locally monitoring the changes in air pollution and reducing the effects of climate change is highly desirable. Particularly, low-cost solid-state sensors are promising candidates for monitoring and controlling environmental quality by preserving air and environment quality and improving human health. Currently, sulfur oxides, the most common pollutant emitted from various sources, are detected and measured via various technologies, including IR spectroscopy and gas chromatography. However, these methods are expensive and time-consuming and thus not suitable for real-time and continuous monitoring applications.
Typically, commercial sensors for detecting sulfur oxides need to operate above 500 ˚C at relatively higher power to improve its detection and regeneration and electrolyte stability. Lately, remarkable efforts have been devoted to improving continuous SO2 monitoring. Environmental sensors capable of detecting a wide range of environmental pollutants are fundamental in the detection, real-time monitoring and analysis of the potential threats to develop mitigation measures. Researchers have been focusing on developing a combination of different material classes for measuring and tracking a wide range of environmental pollutants. The integration of lithium solid-state electrolytes into gas detecting sensors could overcome the above challenges. Li-garnet Li7La3Zr2O12 (LLZO)-based sensors have proved effective in tracking CO2. Interestingly, its hardware and electrochemistry could be developed further to extend its application to other pollutants like sulfur oxides.
To this note, Dr. Moran Balaish and Professor Jennifer Rupp from the Massachusetts Institute of Technology developed a new and novel approach for material selection, electrochemistry and the design of a Li-garnet LLZO-based electrochemical sensors. Although the proposed sensors could detect a wide range of gases, the main target was the highly corrosive and pollutant SO2. Their main objective was to widen the application of Li-Garnet sensors to detect, track and monitor environmental changes and promote the health and safety of humans. The original research article is currently published in the journal, Advanced Materials.
The authors showed that by considering the stability factors such as keeping the conductivity and Li-garnet phase constant when the sensor was exposed to SO2, the device’s functionality was successfully achieved and validated using Li-garnet solid electrolyte and Li2SO4–CaSO4–LLZO electrodes. Novel configurations based on battery field were utilized to achieve sufficient triple phase boundary. The SO2 sensor was operated at a temperature of 480 ˚C with sensitivities ranging from 8 to 49 mV and response time of 4 – 60 min depending on SO2 concentration and the electrode configuration. The electrolyte and the electrode achieved a remarkable theoretical sensitivity of 47.7 mV at a lower sensor operating temperature of 240 ˚C. Notably, this sensor outperformed the previously reported SO2 electrochemical sensors.
In summary, the Balaish-Rupp study demonstrated their new approach is able to widen the application of Li-garnet solid electrolytes beyond batteries to track pollutants other than CO2 under different environmental conditions. The proposed materials selection and sensor design provided the first guidance for real-time and continuous monitoring of SO2 in miniaturized applications. In addition to tracking CO2 and SO2 pollutants, the approach could be extended to track hydrogen sulfide and nitrogen oxides. The authors explained that the study would expand the application of Li-garnets sensors to monitor a wide range of environmental conditions, a key contribution to the effort to improve environment quality and human health.
Balaish, M., & Rupp, J. (2021). Widening the Range of Trackable Environmental and Health Pollutants for Li‐Garnet‐Based Sensors. Advanced Materials, 33(20), 2100314.