University of California, Irvine researchers have developed a method which has demonstrated that by controlling the grain structure of a palladium nanowire, nanowires operating in either the RH2 (+) or the RH2 (-) modes can be obtained.
The single palladium nanowires developed by UC Irvine researchers are capable of detecting hydrogen below 1-2% (Load-of-detection of Hydrogen below 1-2%). The detection also rapidly occurs within 1 to 5 seconds.
When these hydrogen sensing single palladium nanowires detect the presence of hydrogen, their resistance increases. The change in resistance can be measured, and when there is a specific increase in resistance, this reveals that there is the presence of hydrogen.
UC Irvine researchers have developed a method which has demonstrated that by controlling the grain structure of a palladium nanowire, nanowires operating in either the RH2 (+) or the RH2 (-)modes can be obtained. Superior H2 sensing performance, including response times in the 15 second range at high H2 concentrations (Hydrogen Gas) and a LODH2 (Load-of-Detection) of 2 ppm have also been demonstrated for single Pd nanowire sensors operating in the RH2 (+) mode that did not break upon exposure to H2.
Since 2002, palladium nanostructures have been used in a variety of innovative ways as resistor based hydrogen sensors. These sensors can be categorized according to the mechanism by which they transducer hydrogen: Sensors that derive their signal from the volume change associated with the alpha to beta phase transition generally show decreased resistance in the presence of hydrogen (i.e., RH2 (-)) while those that measure the increased resistance of the PdHx relative to Pd show an increased resistance upon H2 exposure (i.e., RH2 (+)).
Two dimensional palladium nanoparticulate films fall into the first category. An attribute of these systems is that they often have rapid response times (< 1s) that mimic the early palladium nanowire arrays, but they are much easier to fabricate.
Researchers in the field have electrodeposited single palladium nanowires and showed that these function as H sensors in this RH2 (-) mode. A RH2 (-) sensor was also produced by using a focused ion beam to cut a nanotrench with width 100-400 nm into a palladium microwire. With a few exceptions, RH (-) sensors show a LODH2 in the 12%range coinciding with the threshold for the alpha to beta phase transition.
A lower LODH2 can be obtained for systems capable of functioning in the RH2 (+) regime because the increased resistance of PdHx can be detected well below the 12% threshold for the alpha to beta phase transition, often at the expense of slower sensor response and recovery times. Still other researchers have recently showed that a sensitive RH2 (+) hydrogen sensor is obtained when carbon nanotubes arrayed between two electrical contacts are electrochemically decorated with palladium nanoparticles. These sensors showed a LODH2 of 100 ppm with response times in the 5-10 minute range.
The disclosed single palladium nanowire sensors have many advantages over the previous utilized methods. The invention generally has the strengths of the previous methods without associated weakness.
Like the previous RH2(+) methods, the disclosed method can detect levels of hydrogens in ranges lower than 12%. In fact, the invention can detect hydrogen in the range of 1-2%. Unlike the previous RH2(+) methods, these sensors have a much faster response rate in the range of 1 to 5 seconds. In terms of the response rate, the invention is similar to the previous RH2(-) methods of sensing as they have a rapid response time. Therefore the invention combines the positive attributes of previous methods, without having their associated drawbacks.
The nanowire can also be exposed to hydrogen without fracturing for up to concentrations of approximately 10% hydrogen. By comparison, some of the other previously created palladium based sensors would fracture at 2% hydrogen concentrations.
1) Rapid response rate: The invention can detect the presence of hydrogen within 1 to 5 seconds.
2) Improved measuring capability: The invention is capable of measuring hydrogen levels below 1-2% and has a rapid response time upon detection. The invention can detect hydrogen concentrations down to 2ppm.
3) Improved durability: The invented wires are exposable to hydrogen for concentrations up to approximately 10% without fracturing.
|United States Of America||Issued Patent||8,499,612||08/06/2013||2009-611|
The invention has been tested successfully, and the detailed results of the test are published in the following research paper:
Fan Yang, David K. Taggart and Reginald M. Penner. “Fast, Sensitive Hydrogen Gas Detection Using Single Palladium Nanowires That Resist Fracture “ Nano Letters. Vol.9, No.5 2177-2182 (2009)