In this article, AZoNano discusses how nanomaterials could be used to improve the efficiency and sensitivity of hydrogen gas detection.
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Why is Hydrogen Gas Detection Important?
The demand for energy will increase systematically in the next few decades, which can lead to greater utilization of non-renewable fossil fuels that are responsible for air pollution and global warming. Hydrogen produced through solar water splitting is considered a suitable alternative to fossil fuels as it is an abundant and clean energy source.
However, safety is a critical issue in hydrogen energy applications as hydrogen-air mixtures are highly flammable and explosive. Thus, using hydrogen sensors for timely leak detection is essential to ensure the safe use, transport, and production of hydrogen as a fuel source.
An effective hydrogen sensor for leakage detection must possess high selectivity and sensitivity, rapid response/recovery, stable functionality, and low power consumption. Typically, long-lasting, easy-to-maintain, and low-cost sensors with a compact design are used to detect hydrogen leakages.
In recent years, technological developments in nanotechnology and synthesis methods have facilitated the use of several nanomaterials as hydrogen sensing materials. Several studies have been performed to evaluate the feasibility of using nanomaterials for hydrogen gas detection based on their unique sensing responses, operating environments, and sensing mechanisms.
Advantages of Nanomaterial-based Hydrogen Gas Sensors
Extremely High Surface-to-Volume Ratio
Large exposed sensing material surfaces ensure a high density of defects, such as dangling bonds or vacancies, to improve electron transfer. Several studies have demonstrated that optimized particle sizes can improve the sensing performance of nanomaterial-based gas sensors.
Low Operating Temperatures
The operating temperature is lower in nanomaterial-based gas sensors than in traditional bulk material-based gas sensors due to the creation of adsorption sites by dangling bonds on the nanomaterial surface.
Presence of Unsatisfied Bonds
The unsatisfied bonds on the nanomaterial surface enable surface functionalization and activation towards the target/hydrogen gas in sensing applications. Thus, the sensing performance can be improved through precise control and surface engineering methodologies.
Application of Nanomaterials for Hydrogen Gas Detection
Gas sensors based on palladium (Pd) nanoparticles and their combination can detect hydrogen gas at room temperature. However, the size of the sensors significantly affects their sensing performance. For instance, a smaller sensing structure/cluster leads to better sensing performance towards hydrogen with low power consumption due to a higher reactive surface.
However, the low ambient operating temperature can increase the sensor surface humidity rate, decreasing sensor sensitivity and response. Additionally, the discontinuity and small size of the sensing materials can lead to an extremely low conductivity in the nanostructures, which induces high electrical noise and affects the sensor response.
Suspended, self-heating, palladium-decorated silicon nanowires (Pd-SiNWs) have been developed for high-performance hydrogen gas detection with enhanced sensitivity. The suspended SiNWs significantly reduce power consumption by decreasing the heat loss through the substrate.
Additionally, a joule heating method has been developed for suspended Pd-SiNWs to significantly improve their response to hydrogen gas/sensing performance without affecting the sensitivity. The suspended Pd-SiNWs manufactured using the physical vapor deposition (PVD) method demonstrated a 0.01% low detection limit at 200-400 oC operating temperature and 10 s/30 s response/recovery time at 0.1% hydrogen.
Several researchers have used the surface acoustic wave (SAW) principles to improve the performance of Pd-based sensors at room temperature. For instance, a Pd–nickel (Ni) alloy thin film-coated SAW hydrogen detection sensor has been developed that demonstrated high stability.
Specifically, the response time of the 40 nm Pd–Ni alloy thin film was less than 10 s at room temperature. Additionally, the greater thickness of the Pd-Ni film led to higher sensitivity. The sensor also displayed a half-year detection error of about 3.7%, indicating long-term stability.
Metal oxide nanostructures such as zinc oxide, tin (IV) oxide, and copper (I) oxide nanorods or nanowires with heterojunction structures have displayed high sensitivity to various gases, including hydrogen. However, noise in the sensing signals, inhomogeneity of hydride reaction, and low conductivity are the major disadvantages of using these structures.
Graphene and its derivatives have a high sensitivity and low detection limit and can operate efficiently at low temperatures. Their unique electronic properties and structures ensure low electronic noise and high electron mobility.
However, adequate information on the chemical stability of graphene-based materials operating under specific conditions required by chemical processes in the sensing layer is unavailable. Thus, only a few reliable graphene-based hydrogen detection sensors are available in the market that can meet industry safety requirements.
In a recent study published in the journal Scientific Reports, researchers investigated the feasibility of using graphene decorated by Pd nanoparticles for hydrogen detection applications.
Researchers developed a novel method to deposit uniformly distributed, small-size, and high-density Pd nanoparticles on graphene to connect the Pd precursors to graphene through π–π bonds without introducing additional defects in the hexagonal carbon lattice.
They used this new method to synthesize hydrogen sensors on three-inch silicon wafers. The fabricated sensors demonstrated high sensing performance at room temperature, with a shorter recovery time under light illumination. Thus, the new deposition method can effectively facilitate the mass fabrication of graphene sensors for hydrogen detection.
In another study published in the journal Nature Materials, researchers proposed a plasmonic metal–polymer hybrid nanomaterial concept for hydrogen detection. In this concept, the polymer coating decreases the activation energy required to transport hydrogen into and out of the plasmonic nanoparticles. At the same time, the deactivation resistance is provided through a tailored tandem polymer membrane.
Thus, this concept enabled subsecond sensor response times when the signal transducer possesses an optimized volume-to-surface ratio offered by nanoparticles. Moreover, the sensor limit of detection was improved, hydrogen sorption hysteresis was suppressed, and the sensor operated efficiently in demanding chemical environments without any indication of long-term deactivation.
Thus, this study displayed effective strategies to fabricate next-generation optical gas sensors with functionalities optimized by hybrid material engineering that can meet stringent performance targets.
To summarize, nanomaterial-based sensors can be used effectively for hydrogen gas detection. However, more research is required to develop more efficient nanomaterial surface functionalization and surface activation methodologies to improve the operation of nanomaterial-based gas hydrogen sensors.
References and Further Reading
Wang, B., Sun, L., Schneider-Ramelow, M., Lang, K.-D., Ngo, H.-D. (2021). Recent Advances and Challenges of Nanomaterials-Based Hydrogen Sensors. Micromachines, 12(11). https://www.mdpi.com/2072-666X/12/11/1429
Tang, X., Haddad, P. -A, Mager, N., Geng, X., Reckinger, N., Hermans, S., Debliquy, M., Raskin, J.-P. (2019). Chemically deposited palladium nanoparticles on graphene for hydrogen sensor applications. Scientific Reports, 9(1), pp. 1-11. https://www.nature.com/articles/s41598-019-40257-7
Nugroho, F. A. A, Darmadi, I., Cusinato, L., Schreuders, H., Bannenberg, L. J., Bastos, A., Kadkhodazadeh, S., Wagner, J. B., Antosiewicz, T. J., Hellman, A., Zhdanov, V. P., Dam, B., Langhammer, C., Susarrey-Arce, A. (2019). Metal–polymer hybrid nanomaterials for plasmonic ultrafast hydrogen detection. Nature Materials, 18(5), pp. 489-495. https://www.nature.com/articles/s41563-019-0325-4
Llobet, E., Navarrete, E. (2019). Nanomaterials for the Selective Detection of Hydrogen at Trace Levels in the Ambient. Handbook of Ecomaterials. doi.org/10.1007/978-3-319-68255-6_12