High-Sensitivity H2S Gas Sensor Based on Perovskite Nanoparticles

As the consequences of poor quality become increasingly known, air pollution has become a significant concern. Quality management in densely populated areas is now strong component of many public health action plans.  

Image Credit: Amelia Martin/Shutterstock.com

To monitor and manage air quality in crowded areas, the development of sensitive and selective environmental gas sensors is critical. Hydrogen sulfide (H₂S) s a life-threatening gas produced from natural sources including sulfate-reducing hydrocarbons and the separation of sour gases.

Nanomaterials are implemented as sensing components to sensor devices to improve their effectiveness by allowing for a higher concentration of reactive sites due to their high surface-to-volume ratio.

Perovskite materials, such as those with the general formula AMX₃, have seen a lot of research interest in recent years, with “A” representing either an inorganic or organic cation, “B” representing a metal cation, frequently Pb, and “X” representing a halide anion.

In this study, researchers employed the hybrid organic perovskite formamidinium lead bromide (FAPbBr₃, where FA⁺: CH(NH₂)²⁺), a material with excellent optical luminescence, good charge transport, and great sensitivity to specific gas molecules.

Researchers developed a polycrystalline FAPbBr₃ as an H₂S gas sensor in which the gas-sensitive components are perovskite grains. The device’s electrical conductivity changed by the presence of low quantities of H₂S gas.

A solution-based technique was used to make the FAPbBr₃ perovskite. The FAPbBr₃ nanoparticles are placed on a glass substrate using interdigitated electrodes that have been prefabricated. With a band edge absorption at 580 nm corresponding to a band gap of 2.13 eV, the constructed sensors displayed a robust sensitivity to optical light.

The sensors’ sensitivity and reaction time are examined, and the results show that they have a high sensitivity to H₂S, as low as 0.5 ppm, and a quick response time.

Methodology

The Inverse Temperature Crystallization (ITC) method was used to generate small millimeter-sized FAPbBr₃ crystals from a 1 M solution of PbBr₂/FABr in DMF:GBL (1:1 v/v)

A high-resolution transmission electron microscope (TEM) was used to create high-quality pictures that allowed the assessment of grain size and shape. The FAPbBr₃ dispersion was placed on molybdenum grids and allowed to dry for this purpose. Using an Empyrean XRD diffractometer, X-ray diffraction (XRD) was performed, allowing the composition and crystal structure of FAPbBr₃ to be determined.

The gas response of the devices was evaluated in a Teflon chamber, with each device mounted on a ceramic stage with an adjustable temperature and a K-type thermocouple monitoring the temperature.

For the gas reaction research, H₂S gas was mixed with air utilizing Bronkhorst mass flow and control devices and then injected into the Teflon chamber while sealed. The adsorption of H₂S gas on nanoparticles alters the charge distribution on their surfaces, resulting in a change in their electrical conductivity.

Results and Discussion

Figure 1a shows a picture of typical millimeter-sized FAPbB₃ crystals before crushing. TEM is used to characterize the grain size and shape of the produced FAPbBr₃ grains, as illustrated in Figure 1b. The figure depicts nanometer-sized semicircular grains with an average size of 23 ± 8 nm. XRD is used to show the composition of FAPbBr₃, as shown in Figure 1c.

Figure 1. (a) Picture of the synthesized FAPbBr₃ grains. (b) TEM image of the crushed FAPbBr₃ grains. (c) XRD spectrum of FAPbBr₃ with Miller indices on the figure. Image Credit: Ayesh, et al., 2022

The current–voltage characteristics of two FAPbBr₃ sensors are shown in Figure 2, with the voltage scanned from −10 V to +10 V. The data on dark current demonstrates some asymmetry among positive and negative voltages, with dark current values of −6 nA and −2 nA for sensors Q1 and Q2, respectively, at −5V.

Figure 2. Current voltage characteristics of two FAPbBr₃ sensors, acquired in the dark and also under semi-light room conditions. Image Credit: Ayesh, et al., 2022

The optical photocurrent recorded from one FAPbBr₃ sensor as a function of wavelength, recorded at various bias voltages, is shown in Figure 3. At a wavelength of 580 nm, the photocurrent response sharply decreases, corresponding to the material bandgap at 2.13 eV.

Figure 3. Optical photocurrent measured from one FAPbBr₃ sensor as a function of wavelength, acquired under three bias conditions of 1 V, 2 V, and 3 V. The photocurrent response edge at 580 nm corresponds to the material bandgap at 2.13 eV. Image Credit: Ayesh, et al., 2022

At room temperature (∼25 °C), Figure 4a illustrates the sensor gas reaction against H₂S gas at various concentrations. Because FAPbBr₃ is light-sensitive, the gas response test is performed in the dark (Figure 4b). The sensor’s reaction to H₂S gas concentration follows a similar pattern to that seen under semi-light illumination, while the response signal is smaller (the only change of the response is in the intensity upon exposure to light).

Figure 4. (a) Sensor gas response at different gas concentration while the sensor is inside the Teflon chamber and room light is on. (b) Electrical gas response of the sensor as a function of H₂S concentration while room light is on and the dark measurements. Image Credit: Ayesh, et al., 2022

The I(V) characterization that was performed during and after exposure to H₂S gas, as shown in Figure 5, supports this process. Due to the suspension of free electron creation, the post-exposure I(V) characteristics exhibit lower conductance than those seen during exposure, as shown in the figure.

Figure 5. I(V) characterization of FAPbBr₃ based sensors during and post exposure to H₂S gas. Image Credit: Ayesh, et al., 2022

Gas sensor stability is a crucial test for determining a gas sensor’s suitability for several operating cycles. As shown in Figure 6, the fabricated sensors are evaluated for stability and reversibility for 10 cycles against 10 ppm at 25 °C. The reaction time of the sensors as a result of H₂S concentration is shown in Figure 6b for both semi-light and dark instances.

Figure 6. (a) Gas response stability test at 10 ppm of H₂S performed at room temperatures. (b) Response and recovery times of the sensor for both semi-light and dark cases. Image Credit: Ayesh, et al., 2022

The figure shows that for varying H₂S concentrations, the recovery time is nearly consistent, with average values of 1.6 minutes for semi-light and 1.4 minutes for dark. The dark case’s faster recovery time might be owing to a smaller concentration of photo-generated free electrons. When it comes to safety applications, however, the sensor’s reaction time is a more essential consideration.

Table 1 compares the performance of the current sensor to that of recently reported sensors.

Table 1. Response of recently reported H₂S sensors based on perovskites. Source: Ayesh, et al., 2022

As a result, when compared to stated values for similar systems for H₂S sensors, the constructed sensors have a faster reaction time.

Conclusion

Perovskite nanoparticles of metal halide perovskite formamidinium lead bromide were used to make high-sensitivity conductometric H₂S gas sensors (FAPbBr₃). A solution-growth approach was used to make the nanoparticles.

The nanoparticles have a cubic shape with an average size of 23 ± 8 nm. FAPbBr₃ has a bandgap of 2.13 eV, according to photocurrent experiments. Under ambient room circumstances, the sensors showed remarkable sensitivity to H₂S, with readings as low as 0.5 ppm.

The sensors worked in both dark and semi-light situations, with a higher response in semi-light due to the photosensitivity of the nanoparticles. Sensors are also reliable for several test cycles, with minimal response and recovery times of 0.2 and 0.6 minutes, respectively, and low power consumption because the sensor does not need to be heated. As a result, sensors might be regarded suitable for prototype applications.

Journal Reference:

Ayesh, A.I., Alghamdi, S.A., Salah, B., Bennett, S.H., Crean, C., and Sellin, P.J. (2022) High sensitivity H₂S gas sensors using lead halide perovskite nanoparticles. Results in physics, 35, p.105333. Available Online: https://www.sciencedirect.com/science/article/pii/S2211379722001152.

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