KRISS Develops Saltwater-Processed Graphene Sensor for Ultrafast Harmful Gas Detection at Room Temperature

- Heater-free chlorinated graphene sensor significantly improves sensitivity, response, and recovery for continuous monitoring in wearable and environmental applications -

The Korea Research Institute of Standards and Science (KRISS, President Dr. Lee Ho Seong) has successfully developed a chlorinated graphene (Cl-Gr) gas sensor that uses readily available saltwater to rapidly detect and recover from harmful gases at room temperature. Because the sensor can operate without a separate heating element, it significantly improves the prospects for practical gas sensors in compact devices, where their use has long been limited by power consumption and heat generation.

Gas sensors are essential devices installed in locations where harmful gas leaks may occur, such as underground parking lots, boiler rooms, and pipelines at industrial sites. Nitrogen dioxide (NO₂), in particular, is a major air pollutant emitted from vehicle exhaust and factory smoke. As it is harmful to human health, precise detection and continuous monitoring are critical. However, conventional sensor technologies often require the sensing material to be heated to several hundred degrees Celsius, resulting in high power consumption and a considerable heat burden. Graphene sensors, which have drawn attention as an alternative, can operate at room temperature, but their slow recovery has limited their use in continuous monitoring.

▲ Chlorinated graphene-based gas sensor developed by KRISS

(A chlorinated microscale graphene channel enables ultrafast detection of nitrogen dioxide (NO2) at room temperature)

The KRISS research team addressed this issue through an electrochemical process using an aqueous sodium chloride (NaCl) solution, commonly known as saltwater. When saltwater is dropped onto the surface of graphene and a voltage is applied, chlorine species in the solution uniformly bond to the graphene surface, enhancing the sensor's performance. Unlike conventional methods that directly use toxic chlorine gas or hydrochloric acid, or require high-temperature and high-pressure processes, this approach simplifies the process without using hazardous gases, improving safety and reducing manufacturing costs.

The developed sensor showed approximately 2.5 times higher sensitivity to nitrogen dioxide at room temperature than conventional sensors. Its response time was reduced by 75.8%, from 157 seconds to 38 seconds. In particular, the recovery time, which had been considered the biggest limitation, was reduced by 86.4%, from 1,485 seconds to 202 seconds, cutting the time required before the next measurement from about 25 minutes to around 3 minutes.

The researchers explained this mechanism through density functional theory (DFT) calculations. Chlorinated graphene has a strong affinity for nitrogen dioxide while also interacting readily with oxygen in ambient air. When the sensor is exposed to clean air after gas detection, oxygen molecules displace nitrogen dioxide molecules and occupy their sites on the graphene surface, enabling rapid recovery at room temperature without an external heat source.

This technology is well suited for continuous monitoring, as it operates at room temperature without a heater while offering both high sensitivity and fast recovery performance. It is expected to provide an optimized solution for applications such as wearable devices, including smartwatches, and environmental monitoring networks.

▲ Research team behind the chlorinated graphene gas sensor

(From left: Dr. Kim Yeonhoo, Principal Research Scientist; Ms. Oh Jaeyeon, Ph.D. Student)

Dr. Kim Yeonhoo, Principal Research Scientist at the Semiconductor and Display Metrology Group of KRISS, said, "We improved the slow recovery speed, which had been the greatest weakness of graphene sensors, using a safe material as simple as saltwater. By lowering the technical barriers that have hindered the miniaturization and low-power operation of gas sensors, we expect this technology to be expanded to a wide range of applications, including smartphones and wearable devices."

▲ Cover image for the December 2025 issue of "Journal of Materials Chemistry A" featuring KRISS's lorinated graphene gas sensor research

This research was supported by KRISS's basic research program and the Creative Convergence Research Program of the National Research Council of Science & Technology (NST). From KRISS, Dr. Kim Yeonhoo participated as a co-corresponding author, and Ms. Oh Jaeyeon, a Ph.D. student, participated as a co-first author. The study was conducted in collaboration with research teams led by Prof. Lee Donghwa of POSTECH, Prof. Hong Byung Hee of Seoul National University, and Prof. An Seongpil of Sungkyunkwan University. The results were selected as a front cover article for the December 2025 issue of 'Journal of Materials Chemistry A', an international journal in the field of materials chemistry.