Pd films on soft substrates: a visual, high-contrast and low-cost optical hydrogen sensor

For the rapid development of the hydrogen economy, a reliable and low-cost hydrogen sensor appears to be extremely important. Here, we first show that a palladium film deposited on polydimethylsiloxane (PDMS) can obtain an exceedingly high-reflectance contrast of 25.78 over the entire visible band upon exposure to 4 vol% hydrogen gas (H 2 ) mixed with nitrogen gas. This high-reflectance contrast results from the surface deformation induced by the volume inflation after exposure to H 2 , leading to the transition of the near-specular surface to a diffusing surface. In addition, a change in brightness is readable by naked eye upon exposure to H 2 with various concentrations from 0.6 to 1 vol% under the illumination of a fluorescent tube. Furthermore, this sensor possesses an excellent recyclability and quick response time of a few seconds. Compared with Pd nanostructure-based hydrogen sensors, this visual, high-contrast and low-cost sensor is of great potential for practical hydrogen sensing. Detecting hydrogen changes with the naked eye A simple, low-cost sensor, designed for remotely detecting dangerous hydrogen levels, is extremely desired in hydrogen-related applications. Chongjun Jin at China’s Sun Yet-sen University, Jianfang Wang at the Chinese University of Hong Kong and co-workers have built a new type of optical hydrogen sensor by sputtering palladium on an elastic slab. As hydrogen was loaded, the palladium film would wrinkle deeply, namely, switching from the mirror-like surface to a coarse one. This phenomenon was not found in the palladium film on inelastic substrate. This hydrogen-induced surface deformation endows the sensor with a dramatically high reflectance change throughout the visible band and thus enables a distinct eye-readable change in color from dark to bright. These results offer great potential for developing inexpensive and sensitive eye-readable hydrogen sensors.