Title : Flexible hydrogen leak detectors
Hydrogen is one of the possible replacements for fossil fuels in the future. However, appropriate safety barriers are required due to hydrogen's high flammability and diffusivity. One such barrier is a flexible detector for hydrogen leaks. Commercially available detection tapes can be wrapped around hydrogen-carrying equipment such as pipe flanges or valves. The tape enables detection of hydrogen leaks by changing color. Such tapes require visual observation to detect leaks and camera-based observations are prone to errors due to blindspots. In contrast, chemiresistive hydrogen detectors can continuously read the detector output and signal an alarm accordingly. Palladium (Pd) is commonly used in the fabrication of chemiresistive sensors due to its high selectivity towards hydrogen. Under ambient conditions, palladium can absorb hydrogen to form a hydride, which has a higher resistance than pure palladium. This increase in resistance is indicative of the presence of hydrogen. Thus, a flexible chemiresistive leak detector can signal the presence of hydrogen without depending on visual observation. Detectors having faster responses enable early leak detection, thereby decreasing the risk of accidents. Palladium nanostructures have exhibited very fast response times and therefore have been widely studied in this regard. Thin polymer sheets, like polyimide, have excellent dielectric properties and excellent heat resistance. Large-area polyimide substrates are also commercially available at a low cost, thereby being useful as a substrate material for flexible leak detectors. In this work, electrically conductive Pd nanostructures were deposited on polyimide, using aluminium foil and a Pd salt solution as the sole precursors. This fabrication approach is a bottom-up process performed under ambient conditions . The detectors could repeatedly respond and recover to step-changes in hydrogen concentration, with nitrogen as the carrier gas. However, the detector response and recovery became slower with an increasing number of exposure cycles (t90 ~ 83 s @ 3.6% H2). This change is attributed to the α → β phase transitions of the palladium hydride creating mechanical stresses in the Pd lattice. Alloying Pd with other metals is one strategy to mitigate this phase transition, e.g., Pd-Pt nanostructures have been shown to exhibit faster responses in comparison to Pd. Therefore, Pd-Pt nanostructures were deposited on polyimide by simply modifying the precursor solution. These bimetallic nanostructures exhibited faster response times (t90 ~ 40 s @ 3.6% H2) than the monometallic Pd nanostructures. While testing in air, the oxygen molecules interact with Pd to form Pd-O, resulting in decreased sensitivity and longer response times. In this talk, I will describe how these challenges were overcome and analyze the results of hydrogen leak detection tests.
Audience Take Away:
- This metal deposition method could be used in other areas, such as catalysis, where Pd and Pt are utilized. A study has also shown that aluminium coupled with activated carbon could be used as a reducing agent for recovering heavy metals such as Co2+ and Ni2+ from wastewater [Choi, S., Jeon, S., Park, I., Ito, M., & Hiroyoshi, N. (2021). Enhanced Cementation of Co2+ and Ni2+ from Sulfate and Chloride Solutions Using Aluminum as an Electron Donor and Conductive Particles as an Electron Pathway. Metals, 11(2), 248].
- The underlying cause for deposition of Pd could be examined in detail and possibly applied to other metals as well
- The method developed in this work utilizes relatively less expensive chemicals and is carried out under ambient conditions compared to other techniques such as lithography.