- Nano Express
- Open Access
Influence of Conditions of Pd/SnO2 Nanomaterial Formation on Properties of Hydrogen Sensors
© The Author(s). 2017
- Received: 6 February 2017
- Accepted: 18 May 2017
- Published: 2 June 2017
Metal oxide sensors were created using nanosized tin dioxide obtained by a sol-gel method. Gas-sensitive layers of the sensors were impregnated with PdCl2 solutions of different concentrations to increase sensitivities of the proposed sensors. Influence of different temperature conditions of the sensor formation on the sensor properties was studied. It was found that decreasing duration of high-temperature sensor treatment prevents enlargement of particles of the gas-sensitive materials. It was shown that the sensors based on materials with smaller particle sizes showed higher sensor responses to 40 ppm H2. Obtained results were explained in terms of substantial influence of length of the common boundaries between the material particles of tin dioxide and palladium on the gas-sensitive properties of the sensors. The obtained sensors had possessed a fast response and recovery time and demonstrated stable characteristics during their long-term operation.
- Nanomaterial Pd/SnO2
- Sol-gel method
Nowadays, hydrogen is widely used for chemical synthesis in industry and as environmentally friendly energy source [1–3]. Hydrogen is an explosive gas, and therefore, control of H2 content in areas of its using, transportation, and storage is needed. Gas analysis devices based on metal oxide sensors can be promising to realize such control [4–6].
It is well known that nanosized materials have some unique physicochemical properties, i.e., optoelectronic , magnetic , and catalytic . SnO2 is a perspective material to create the metal oxide sensors due to its chemical inertness, thermal stability, and ability to chemisorb oxygen. That is why nanomaterials based on tin dioxide are very interesting to study as gas-sensitive layers of the sensors to measure H2 in air. Increasing the sensor responses to hydrogen can be achieved by addition in the gas-sensitive layer of the sensors of catalytic active additives including Pd which is one of the most active catalysts in a reaction of hydrogen oxidation [6, 10].
Composition of the sensor material, method of its preparation, and conditions of the material formation can influence on the particle size [11–13] and thus on gas-sensitive properties of the material.
Morphology of the material of the sensor-sensitive layer including its size of particles and their distribution has great importance to create highly efficient metal oxide sensors [14–16]. It is known that decreasing the particle size of the sensor sensitive layer material should increase the sensor response . At the same time, it is known that creation of the sensors requires their high-temperature sintering. However, the high-temperature sintering leads to enlargement of the nanomaterial particles. That is why conditions of a process of the high-temperature sintering of the sensor should prevent the enlargement of the particles and provide simultaneously both mechanical strength of the sensors and their conductivities through formation of contacts between the nanoparticles of the material of the gas-sensitive layer .
Optimal temperature of the sensor sintering which should satisfy the conditions listed above can be achieved by required temperature values and time duration of definite stages of the high-temperature sintering of the sensors. The conditions of formation of the sensor nanomaterial should also provide full completion of crystallization and stabilization of its nanoparticles.
The aim of this work is to study the influence of conditions of formation of Pd/SnO2 nanomaterials with different palladium content on properties of semiconductor sensors to hydrogen.
Synthesis of Nanosized Tin Dioxide
Synthesis of nanosized SnO2 materials was carried out by a sol-gel method. The sample of SnCl4·5H2O (m = 1.5 g) was dissolved in 15 ml of ethylene glycol. The obtained solution was evaporated at 110–120 °C. After evaporation of ethylene glycol, a dark brown gel was formed. The resulting gel was dried at 150 °C to form a xerogel. The xerogel was grinded up and placed on a ceramic plate. To obtain nanosized SnO2, thermal decomposition of the xerogel was carried out in air using a high-temperature furnace Gero (Germany). Nanosized SnO2, carboxymethyl cellulose, and PdCl2 were used to obtain the gas-sensitive materials.
Preparation of Adsorption-Semiconductor Sensors
Methods of Measurement
To measure a value of the sensor signal, the sensors were placed into chambers and connected to a special electric stand . Measuring was carried out using analyzed gas flow with a rate of 400 ml/min. Required sensor temperature was ensured by a definite value of voltage on the sensor heater. Measurement of the sensor temperature was carried using a pyrometer Optris Laser Sight (Optris, Germany). The sensors were stabilized by aging at 400 °C during 1 week in air with periodical treatment of the sensors by the hydrogen-air mixture with 1000 ppm H2 before measuring the gas-sensitive properties.
Ratio of a value of the electrical resistance of the sensor in air (R 0) to a value of its electrical resistance in the presence of 40 ppm H2 (R H2) was chosen as a measure of the sensor response. The sensor response time (t 0.9) was estimated as a time required for the sensor to reach 90% of an equilibrium signal value when air is replacing by an analyzed gas. The recovery time (τ 0.1) was estimated as a time required for the sensor to return to 10% above the initial signal in air when the analyzed gas is replacing by air.
The characteristics of the sensors were studied using hydrogen-air mixtures with various concentration of H2. Mixtures of air with H2, CO, CH4, and H2 and CO or H2 and CH4 were used to estimate selectivity of the obtained sensors. All analyzed gas mixtures were prepared and tested in Ukrainian Centre of Certification and Metrology.
Stabilities of the responses to 40 ppm of H2 for the sensors S2 (S-67 and S-69) during 6 months of their operation were studied.
Determination of the specific sensor material surface was carried out by Brunauer-Emmett-Teller (BET) method.
Content of palladium in the sensor materials was determined by an atomic absorption method using a spectrophotometer AAS1N Carl Zeiss (Jena, Germany) with a flaming atomizer. Atomization of palladium was performed in acetylene-air flame (2350 °C).
Study of phase composition was performed using a diffractometer Bruker D & Advance (radiation CuKα). Identification of sample phase was carried out by comparison of obtained results and published crystallographic data.
Study of morphology of the sensor materials by TEM method was performed using a transmission electron microscope SELMI PEM-125 K with an accelerating voltage of 100 kV. The particle size analysis based on TEM images was carried out using the Kappa Image Base program. To obtain information on the particle size distribution for the obtained nanomaterials, about 300 particles in TEM image were taken into account.
The samples of the obtained nanomaterials were studied by FESEM method using a field emission scanning electron microscope JEOL JSM-6700F (JEOL Ltd., Japan) and HRTEM method using a transmission electron microscope JEM-2100F (JEOL Ltd., Japan).
Thickness of the sensor layer was estimated using a scanning electron microscope JEOL JSM-6060LA (JEOL Ltd., Japan) with a working voltage of 30 kV.
The synthesized nanomaterials based on SnO2  with an average particle size 8 nm were used to create the sensors and study influence of different temperature heating conditions of the sensor preparation on the gas-sensitive properties.
To provide both formation of the sensor conductivity and its mechanical strength, the duration of the sensor heating was reduced up to 80 min with simultaneous increasing of the final temperature of the sensor sintering to 620 °C. Furthermore, the duration of the sensor heating in this temperature mode was increased to 80 min in low-temperature regions of the sintering, namely, at 280 and 410 °C, that corresponded to the temperatures of CMC and palladium chloride decomposition [24–26]. These changes in the low-temperature regions of the sensor formation are caused by necessity of formation of a larger number of the contacts in the sensor material. The increasing of the particle size of the material in the low-temperature regions should not certainly be so intense as it should be at 620 °C. Scheme of more soft temperature heating mode 2 of the sensor sintering is presented in Fig. 1b.
Analysis of TEM micrographs of the obtained sensor materials S2 (Fig. 2b) showed that these materials include particles which were smaller than particles of the sensor material S1 (Fig. 2a): an average particle size of tin dioxide for both studied temperature heating modes 1 and 2 was 17 and 11 nm respectively. Such decreasing of the particle size of the sensor material S2 contributed to an increase of value of tin dioxide specific surface to 47 m2/g instead of 39 m2/g which was found for the sensor material S1.
It was shown that palladium content in the Pd/SnO2 nanomaterials obtained by impregnation of the nanosized SnO2 by solutions of PdCl2 increases when concentration of palladium chloride increases too. In particular, when concentration of PdCl2 solution was changed from 0.05 mol/L to 15 × 10−2 mol/L, the content of palladium additives in the nanomaterials was changed from 0.001 to 0.193 wt%.
According to XRD data, unmodified tin dioxide and Pd/SnO2 nanomaterials with different palladium content obtained in both temperature modes have cassiterite structure with identical lattice parameters a = 0.4738 nm, b = c = 0.3187 nm .
To explain the obtained results, it should be noted that values of the resistance R 0 and sensor response with addition of metals (or oxides) in material of the gas-sensitive layer were provided by formation of common boundaries between particles of the active additives and tin dioxide [19, 27, 28]. When the sensor is heated in air, these boundaries take part in chemisorption of oxygen with localization of electrons from conductivity band of semiconductor. Such chemisorption influences on the values of the electrical resistance of the sensor. In the presence of an analyzed gas, a heterogeneous catalytic reaction oxidation of the gas by chemisorbed oxygen is running on the surface of the semiconductor. The electrons localized at chemisorbed oxygen return to the conductivity band of the semiconductor, and the decrease in the electrical resistance of the sensor is performed. In this case, the stationary oxygen quantity on the sensor surface that occurs as a result of a dynamic equilibrium state of the oxidation reaction will determine the resistance value of the sensor. A change of the value of the sensor resistance when air is replaced by the analyzed gas determines the value of the sensor response. Under identical conditions (the same gas of the definite concentration and the same temperature of the sensor), the value of the electrical resistance of the sensor in air and its change in the presence of the analyzed gas (sensor response) will depend on the length of the boundary between palladium and tin dioxide particles.The palladium content in the sensor material will affect the value of the length of the boundary and thus will determine the properties of the sensor.
As can be seen from Fig. 4a, b, introduction of palladium (up to 0.05% Pd) affects the sensor value R 0 in the same manner independently of the temperature heating mode of the sensor sintering. The observed initial reduction of the value of the sensor electrical resistance may be occurred as a result of existence of metallic palladium which is formed on the sensor surface according to the obtained XPS data . Further increase of palladium content leads to a slight increase in the values of the resistances of the sensors S1 and S2 due to the low oxygen chemisorption at the boundary of a very small length between SnO2 and palladium particles. It should be noted that similar values of the resistances of the sensors S1 and S2 in the range of such low palladium contents indicate no significant influence of palladium on the properties of the sensors which are determined by own properties of tin dioxide in these conditions. It was found that the value of electrical resistance of SnO2 did not practically depend on the sintering temperature of the sensor in the temperature range of 590–620 °C as it was found in [19, 21–23].
Change of the temperature heating mode of creation of the sensors S1 and S2 affects the value of their resistance significantly when palladium content is increased (>0.05% Pd) (Fig. 4a, b). Indeed, the resistance for the sensors S2 have much greater values than those for the sensors S1 in conditions of the same palladium contents in the concentration range of 0.05–0.2% Pd. This is in agreement with the assumption about a stabilizing role of palladium  which prevents the enlargement of the nanomaterial particles, and the soft temperature heating mode 2 of the sensor sintering contributes to this process. The length of the boundaries between particles of palladium and tin dioxide under these soft temperature conditions will be longer for the material S2, and therefore, due to a large quantity of oxygen chemisorbed on the boundaries, the values of resistance for the sensors S2 should be greater than those for the sensors S1. This is confirmed in an experiment (Fig. 4a, b). Formation of the smaller particles for the Pd-containing nanomaterials obtained in the soft temperature conditions of the heating mode 2 was also confirmed by TEM method (Fig. 2b).
Finally, at very high palladium contents, process of Pd particle aggregation can start and it will decrease the length of the common boundaries resulting in decrease in the electrical resistance values of the sensors (Fig. 4b).
It was found that positions of maximum values of the sensor electrical resistances (Fig. 4a, b) and the sensor responses (Fig. 5a, b) for the sensor S2 compared to the sensor S1 are shifted to a region of the higher palladium contents. It can be a result of existence of relatively larger palladium content on the sensor surface in a non-aggregated state for the material SnO2 with smaller size of their particles. Such state of the material will promote increase of the electrical resistance value of the sensor in air and the sensor response to hydrogen.
Change of conditions of high-temperature treatment of the sensors based on Pd/SnO2 led to form smaller particles of nanomaterial of the gas-sensitive layer of the sensor that allowed to reach a significant value of the sensor response (R 0/R H2 = 19.5) to microconcentration of hydrogen (40 ppm) at the sensor temperature 261 °C. The created sensors can measure hydrogen in a wide range of its concentration (2–1089 ppm H2), have a low limit of H2 detection, and demonstrate a fast response and recovery time. The created sensors are stable during their long-term operation.
The authors declare that they have no competing interests.
LO and NM conceived and designed the experiment. ES synthesized the nanomaterials. IM created the sensors. ES and IM provided the sensors’ measurements. LO, NM, and ES wrote the paper. All authors read an approved the final manuscript.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Ross D (2006) Hydrogen storage: the major technological barrier to the development of hydrogen fuel cell cars. Vacuum 80(10):1084–1089View ArticleGoogle Scholar
- Gao F, Zhao G, Yang S, Spivey J (2013) Nitrogen-doped fullerene as a potential catalyst for hydrogen fuel cells. J Am Chem Soc 135(9):3315–3318View ArticleGoogle Scholar
- Hua T, Ahluwalia R, Eudy L, Singer G, Jermer B, Asselin-Miller N et al (2014) Status of hydrogen fuel cell electric buses worldwide. J Power Sources 269:975–993View ArticleGoogle Scholar
- Miller D, Akbar S, Morris P (2014) Nanoscale metal oxide-based heterojunctions for gas sensing: a review. Sensors Actuators B Chem 204:250–272View ArticleGoogle Scholar
- Russo P, Donato N, Leonardi S, Baek S, Conte D, Neri G et al (2012) Room-temperature hydrogen sensing with heteronanostructures based on reduced graphene oxide and tin oxide. Angew Chem Int Ed 51(44):11053–11057View ArticleGoogle Scholar
- Wang Z, Li Z, Jiang T, Xu X, Wang C (2013) Ultrasensitive hydrogen sensor based on Pd0-loaded SnO2 electrospun nanofibers at room temperature. ACS Appl Mater Interfaces 5(6):2013–2021View ArticleGoogle Scholar
- Su X, Luo F, Zhao K, Jia Y, Wang J, Xu J et al (2014) Preparation, microstructure and electromagnetic property of SnO2 powder by co-precipitation method at different calcined temperature. Mater Technol 30(4):218–222View ArticleGoogle Scholar
- Basu S, Wang Y, Ghanshyam C, Kapur P (2013) Fast response time alcohol gas sensor using nanocrystalline F-doped SnO2 films derived via sol–gel method. Bull Mater Sci 36(4):521–533View ArticleGoogle Scholar
- Rashad M, Ibrahim I, Osama I, Shalan A (2014) Distinction between SnO2 nanoparticles synthesized using co-precipitation and solvothermal methods for the photovoltaic efficiency of dye-sensitized solar cells. Bull Mater Sci 37(4):903–909View ArticleGoogle Scholar
- Esfandiar A, Irajizad A, Akhavan O, Ghasemi S, Gholami M (2014) Pd–WO3/reduced graphene oxide hierarchical nanostructures as efficient hydrogen gas sensors. Int J Hydrog Energy 39(15):8169–8179View ArticleGoogle Scholar
- Saha K (2012) Gold nanoparticles in chemical and biological sensing. Chem Rev 112(5):2739–2779View ArticleGoogle Scholar
- Singh A, Sahoo S (2014) Magnetic nanoparticles: a novel platform for cancer theranostics. Drug Discov Today 19(4):474–481View ArticleGoogle Scholar
- Senanayake S, Stacchiola D, Rodriguez J (2013) Unique properties of ceria nanoparticles supported on metals: novel inverse ceria/copper catalysts for CO oxidation and the water-gas shift reaction. Acc Chem Res 46(8):1702–1711View ArticleGoogle Scholar
- Leite E, Weber I, Longo E, Varela J (2000) A new method to control particle size and particle size distribution of SnO2 nanoparticles for gas sensor applications. Adv Mater 12(13):965–968View ArticleGoogle Scholar
- Chen W, Gan H, Zhang W, Mao Z (2014) Hydrothermal synthesis and hydrogen sensing properties of nanostructured SnO2 with different morphologies. J Nanomater 2014:1–7Google Scholar
- Lingmin Y, Xinhui F, Lijun Q, Lihe M, Wen Y (2011) Dependence of morphologies for SnO2 nanostructures on their sensing property. Appl Surf Sci 257(7):3140–3144Google Scholar
- Yamazoe N (1991) New approaches for improving semiconductor gas sensors. Sensors Actuators B Chem 5(1-4):7–19View ArticleGoogle Scholar
- Barsan N, Udo W (2001) Conduction model of metal oxide gas sensors. J Electroceram 7(3):143–167Google Scholar
- Oleksenko L, Maksymovych N, Sokovykh E, Matushko I, Buvailo A, Dollahon N (2014) Study of influence of palladium additives in nanosized tin dioxide on sensitivity of adsorption semiconductor sensors to hydrogen. Sensors Actuators B Chem 196:298–305View ArticleGoogle Scholar
- Fedorenko G, Oleksenko L, Maksymovych N, Matushko I (2015) Semiconductor adsorption sensors based on nanosized Pt/SnO2 materials and their sensitivity to methane. Russ J Phys Chem A 89(12):2259–2262View ArticleGoogle Scholar
- Sokovykh E, Oleksenko L, Maksymovych N, Matushko I (2015) Influence of temperature conditions of forming nanosized SnO2-based materials on hydrogen sensor properties. J Therm Anal Calorim 121(3):1159–1165Google Scholar
- Buvaylo A, Oleksenko L, Maksymovych N, Matushko I, Skolyar G, Derkachenko N (2010) Sensors to hydrogen on the base of nanosized tin dioxide. Mater Sci Nanostructures 3:38–43Google Scholar
- Oleksenko L, Maksymovych N, Buvailo A, Matushko I, Dollahon N (2012) Adsorption-semiconductor hydrogen sensors based on nanosized tin dioxide with cobalt oxide additives. Sensors Actuators B Chem 174:39–44View ArticleGoogle Scholar
- Adel A, Abou-Youssef H, El-Gendy A, Nada A (2010) Carboxymethylated cellulose hydrogel; sorption behavior and characterization. Nat Sci 8:244–256Google Scholar
- Sokovykh E, Oleksenko L, Maksymovych N, Matushko I, Fedorenko G (2014) DTA-DTG study of PdCl2 /SnO2 decomposition for creation nanosized materials of semiconductor sensors of explosive gases. 34th International Conference on Vacuum microbalance and thermoanalytical techniques (ICVMTT34) and International Conference Modern problems of surface chemistry. Kyiv. 58Google Scholar
- Beyler Craig L and Hirschler Marcelo M (1995) Thermal decomposition of polymers. In: Craig L. Beyker, Richard L.P. Custer, W. Douglas Walton, editors. SFPE handbook of fire protection engineering. Quincy, Mass: National Fire Protection Association. Boston: Society of Fire Protection Engineers. p. 110-131Google Scholar
- Green I, Tang W, Neurock M, Yates J (2011) Spectroscopic observation of dual catalytic sites during oxidation of CO on a Au/TiO2 catalyst. Science 333(6043):736–739View ArticleGoogle Scholar
- Jaramillo T, Jorgensen K, Bonde J, Nielsen J, Horch S, Chorkendorff I (2007) Identification of active edge sites for electrochemical H2 evolution from MoS2 nanocatalysts. Science 317(5834):100–102View ArticleGoogle Scholar
- Takeguchi T (2003) Strong chemical interaction between PdO and SnO2 and the influence on catalytic combustion of methane. Appl Catal A Gen 252(1):205–214View ArticleGoogle Scholar
- Bamsaoud S, Rane S, Karekar R, Aiyer R (2012) SnO2 film with bimodal distribution of nano-particles for low concentration hydrogen sensor: effect of firing temperature on sensing properties. Mater Chem Phys 133(2-3):681–687View ArticleGoogle Scholar
- Lee Y, Huang H, Tan O, Tse M (2008) Semiconductor gas sensor based on Pd-doped SnO2 nanorod thin films. Sensors Actuators B Chem 132(1):239–242View ArticleGoogle Scholar