Hydrogen sensing that integrates catalysis/sensing/detection

Recently, Professor Chen Qin’s team from the Institute of Nanophotonics of Jinan University demonstrated a high-sensitivity and low-latency hydrogen sensor that integrates photocatalysis, photosensing, and photoelectric detection by regulating the interface transport behavior of surface plasmon thermoelectrons by gas molecules.

The results were published in Light: Science & Applications under the title “On-Chip Ultrasensitive and Rapid Hydrogen Sensing based on Plasmon-Induced Hot Electron-Molecule Interaction.” Professor Wen Long is the first author of the paper.

The monolithic integrated technical architecture uses surface plasmon thermoelectrons as the medium of photocatalysis, photosensing and photoelectric conversion, which provides a new idea for enhancing the interaction between photons-electrons and molecules and portable optical sensing detection, and has high research and application value.

As a clean energy, hydrogen is of great significance in promoting energy conservation and emission reduction, adjusting the structure of the energy industry, and coping with global climate change. However, hydrogen is difficult to detect when leaking, and it is very easy to cause safety accidents after accumulation, such as the 2011 Fukushima nuclear accident in Japan, which was an explosion caused by hydrogen leakage. In order to better develop and utilize hydrogen energy, fast and highly sensitive hydrogen sensing technology is essential.

At present, the main commercial products are resistive hydrogen sensors with semiconductor oxide systems and palladium (palladium alloy) systems. However, even high-performance resistive sensors can only quickly detect hydrogen concentrations above 500 ppm, cannot alarm in the initial stages of leakage, and often operate at temperatures of 150 °C or higher. Tunable semiconductor laser absorption spectroscopy technology commonly used in gas sensing is difficult to meet sensitivity requirements due to the low absorption coefficient of hydrogen, and the system is complex and expensive. New hydrogen sensing technologies and methods need to be developed.

Surface plasmon optical sensors are a hot topic in this field in recent years, and their technical principle is to use the difference in optical resonance characteristics caused by the change or deformation of plasmon metals under the action of hydrogen as a detection signal, and many remarkable breakthroughs have been made. However, most of the existing optical sensing technologies, including surface plasmon hydrogen sensing, adopt a discrete architecture of sensing unit and detection unit, relying on external high-precision spectrometers for optical sensing signal demodulation, which is not as practical as electrical sensors, and surface plasmon hydrogen sensors that have been reported in the existing literature also have shortcomings in sensitivity and response speed.

The core problem in improving the response sensitivity and speed of optical sensors is how to enhance the interaction between light and matter and achieve perfect translation of the sensing signal. Thanks to the study of the generation, recombination and interfacial transport mechanism of non-radiative attenuation thermoelectrons, surface plasmons are expected to expand from single optical applications to broader application scenarios such as photochemistry (photocatalysis, photoelectrochemistry) and optoelectronic devices (optical emission and light detection).

This paper innovatively combines the characteristics of surface plasmon thermoelectrons in the process of photocatalysis and photoelectric conversion, and proposes a photoelectric hydrogen sensor based on photocatalysis-photosensing-photodetection integration: (Figure 1) The use of hydrogen-sensitive metals to generate in-band transition thermoelectrons through surface plasmon coupling, on the one hand, can enhance and accelerate the catalytic bond breaking reaction at the hydrogen molecule/metal interface, on the other hand, it can cross the metal-semiconductor Schottky junction barrier to form a photocurrent signal related to the concentration of hydrogen molecules, and then realize the highly sensitive and monolithic integration Low latency hydrogen sensing.

Figure 1. Catalytic enhancement and in-situ photoelectric sensing were realized on hydrogen-sensitive metal-dielectric-semiconductor (MIS) junctions by using the transport and interfacial transport behavior of high-energy thermoelectrons in the band transition of surface plasmons.

More interestingly, the high sensitivity of this technique also benefits from the novel physical effects generated by the synergy of multiple physical mechanisms at the MIS junction interface. In this paper, the researchers found that the photovoltammetry (I-V) characteristic curve of the thermoelectron MIS junction is completely different from that of air and hydrogen: as shown in Figure 2 (upper left), the illumination I-V curve of the MIS junction in air is consistent with that of conventional junction optoelectronic devices; After exposure to the hydrogen-containing atmosphere, the illumination I-V curve showed a significant S-line curve around 0V. As shown in Figure 2 (top right), this effect enables a very high switching ratio of the sensing response at zero bias and room temperature. In this paper, combined with the quantum tunneling model of MIS junction, it is revealed that the S-linear I-V characteristics are derived from the modulation effect of hydrogen-induced interface dipole layer on the collection of thermal electrons in the MIS junction.

Figure 2. The main characteristics and performance of thermoelectronic hydrogen sensors proposed in this paper are displayed. (upper left) S-line illumination I-V curve based on the regulation of thermal electron tunneling characteristics by hydrogen-induced interface dipole layer; (top right) The device obtains a much higher hydrogen response switching ratio under illumination conditions than when operating in dark state; (bottom left) Low hydrogen sensing detection limit; (bottom right) Significantly faster response under lighting.

It is very important that this new sensor has the characteristics of simple preparation technology and low cost, without the need for precision graphical process, the formation of disordered metal nanostructures through rapid thermal annealing, with low-cost white LED light source, and does not rely on tunable lasers and spectrometers for signal processing, so it has the advantages of low-cost and portable applications.

Compared with the existing technology, the new principle of hydrogen sensing integrated photocatalysis-photosensing-photodetection proposed in this paper not only combines the catalytic enhancement effect brought by the thermoelectronic interface transfer behavior, but also uses the interfacial polarization layer induced by hydrogen to act on the photoelectric conversion of thermoelectrons, and obtains the performance indicators such as sensitivity and response time, and the detection limit reaches 1 ppm, and at the same time realizes the key technology of sensor chip with low cost, high integration, zero bias and room temperature operation. (Source: LightScience Applications WeChat public account)

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