An international team of researchers has found that the metal hafnium is ideally suited to detecting hydrogen.
Hydrogen has enormous potential as an energy carrier, yet the fact it is both combustible and difficult to detect has hitherto proven an obstacle to its widespread use. Because hydrogen reacts with oxygen, potentially causing explosions, a reliable means of detecting it is vital for any handling applications where the gas is used or could be present. Reliable and accurate hydrogen sensors are also hugely important for leak detection, to prevent the gas leaking into the atmosphere.
Some optical sensors for hydrogen detection do exist. They rely on materials that absorb hydrogen atoms, the process altering the materials’ reflexivity. By measuring changes in reflexivity, information can be gleaned about the amount of hydrogen present in a particular location.
"Until now, pure palladium was mainly used as an optical hydrogen sensor," says Prof. Bernard Dam from TU Delft, who was involved in the new research, in a statement of phys.org. "But over the last few years, we at Delft have shown that a gold-palladium alloy is a much better sensor. Fellow researchers around the world are also studying this." Unfortunately, palladium is unable to detect hydrogen at low pressures.
The new study, published in the journal Nature Communications, shows that hafnium has the sensitivity needed to detect hydrogen at low pressures. Dam says, "The unique property of this material is that it can optically measure a minimum of six orders of magnitude in pressure. The lowest pressure measured is 10-7 atmospheres, but this pressure is determined by the measurement setup. It looks as if a pressure of three orders of magnitude lower could be measured with hafnium, but we need to do more research to confirm this." Another benefit is that the optical properties of hafnium change linearly with the pressure and temperature of the material. "This makes hafnium sensors very easy to calibrate," says Dam.
A potential downside to hafnium as a sensor is that it works best at 120 degrees Celsius. Dam thinks that this challenge can be solved by placing a thin layer of hafnium on top of an optical fibre, before heating the fibre with a warm-up LED.
The study was led by PhD candidate Christiaan Boelsma from TU Delft. The international team also included researchers from KU Leuven (Belgium) and the Rutherford Appleton Laboratory (UK).