Scientists have discovered a mechanism that allows hydrogen sensors to work under visible light, without heating, therefore enabling the sensor to work at room temperature. The discovery, based on nanocrystalline metal oxides, could reduce the energy consumption of the sensor and expand its scope. A hydrogen sensor scheme. Courtesy of Alexander Ilyin. Until now, most research has been devoted to the influence of UV illumination on the sensor properties of nanocrystalline metal oxide to oxidizing gases. But UV LEDs have lower efficiency and are much more expensive than visible LEDs. Researchers at Moscow State University examined the effect of green light irradiation on gas sensing behavior of hydrogen sensors based on nanocrystalline ZnO-In2O3 composites. They analyzed the dependency of the photoactivated sensor response to hydrogen on the fraction of ZnO in the ZnO-In2O3 composite. Based on their findings they proposed a new mechanism of the sensor response under illumination, which considers the transition of the nanocomposite to a nonequilibrium state when it is irradiated. Researchers found that composites based on zinc and indium oxides could significantly increase the sensitivity of the sensor to hydrogen. Samples for the sensor were made from nanocrystalline indium and zinc oxide powders. The structure and particle size were studied using transmission electron microscopy and x-ray diffraction. The temperature of the composite and the concentration of hydrogen were well controlled during the study. The results from this experiment could enable the development of a resistive hydrogen sensor that works under additional illumination without heating. Such sensors are promising not only for effective monitoring of environmental pollution in industrial plants, but also for constant monitoring of air in closed facilities, such as submarines, mines and spacecraft, where the slightest change in the chemical composition could lead to human casualties. “Such sensors can be used in explosive environments or be built into mobile devices without constructing additional heat sink systems,” said researcher Alexander Ilyin. The research was published in Scientific Reports (doi: 10.1038/s41598-017-12547-5).