Toxic ammonia gas 'sniffed out' by sensor

A small ammonia gas sensor that could enable safer hydrogen storage has been developed by engineers in Australia.

An estimated 235 million metric tonnes of ammonia are produced globally, but with ammonia being touted as one of the best ways to store hydrogen for clean fuel — and therefore key to the green energy transition — levels may soon be on the rise.

Given that exposure to high levels of ammonia can lead to chronic lung conditions and irreversible organ damage, having access to reliable and sensitive ammonia detection is critical. Early detection will enable workers to quickly spot potentially dangerous leaks of ammonia gas during transportation of hydrogen, thereby enhancing operational safety.

To assist with this process, researchers at RMIT University, the University of Melbourne and the ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS) have developed the ammonia gas sensor, which acts like an “electric nose”.

Senior lead researcher Dr Nitu Syed — McKenzie Research Fellow from the University of Melbourne, RMIT and TMOS — said the sensor featured atomically thin transparent tin dioxide that can easily track ammonia at much smaller levels than similar technologies.

“The sensor is also able to distinguish ammonia from other gases with more selectivity than other technologies.”

The presence of ammonia in the air changes the electrical resistance of the tin oxide film in the sensor: the higher the level of ammonia, the greater the change in the resistance of the device.

The research team conducted experiments with their sensor in a specially designed chamber to test its ability to detect ammonia gas at various concentrations (5–500 parts per million) under different conditions, including temperature. They also tested the device’s selectivity of ammonia against other gases, including carbon dioxide and methane.

First author, Dr Chung K Nguyen from RMIT University, said their miniaturised sensor offered a safer and less cumbersome way to detect the toxic gas, compared to existing techniques.

“Current approaches to ammonia detection produce accurate measurements but require expensive laboratory equipment with qualified technicians, extensive sampling and preparation,” Nguyen said.

“This process is often time-consuming and not portable, due to the size of the equipment needed. In addition, the manufacturing of today’s ammonia detectors involves expensive and complicated processes to prepare sensitive layers for sensor fabrication.”

The team’s new sensor can instantaneously differentiate between safe and dangerous levels of ammonia in the environment, Nguyen said.

“The reproducible deposition of tin oxide also offers the opportunity for cost-effective mass production of sensing devices,” he said.

The research team hopes to collaborate with industry partners to further develop and prototype the sensor to demonstrate its high-performing sensing capabilities.

Image: Supplied.