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 remained 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.
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.
Saltwater Fix
Korea Research Institute of Standards and Science (KRISS) researchers addressed this issue through an electrochemical process using an aqueous sodium chloride (NaCl) solution, commonly known as saltwater.
When saltwater drops onto the surface of graphene and a voltage 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 reduces by 75.8 percent, from 157 seconds to 38 seconds.
A chlorinated graphene-based gas sensor enables ultrafast detection of nitrogen dioxide at room temperature.
Source: KRISS
In particular, the recovery time, which had been considered the biggest limitation, reduced by 86.4 percent, from 1,485 seconds to 202 seconds, cutting the time required before the next measurement from 25 minutes to around 3 minutes.
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 ends up 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.
Applications
This technology has the capability to work well in continuous monitoring, as it operates at room temperature without a heater while offering high sensitivity and fast recovery performance.
Additionally, it can provide an optimized solution for applications such as wearable devices, including smartwatches, and environmental monitoring networks.
“We improved the slow recovery speed, which had been the greatest weakness of graphene sensors, using a safe material as simple as saltwater,” said Dr. Kim Yeonhoo, principal research scientist at the Semiconductor and Display Metrology Group of KRISS. “By lowering the technical barriers that have hindered the miniaturization and low-power operation of gas sensors, we expect this technology to expand to a wide range of applications, including smartphones and wearable devices.”