Vol. 37, Supplement B (2021)

4.

ZnO is one of the most studied gas sensor materials. Its electrical resistance changes due to the adsorption and reaction of combustible gases, which can be utilized for detecting target gases. To improve its gas sensing characteristics, ZnO nanorods were grown and their sensor responses were measured under UV light. The response to ethanol was improved under UV irradiation, and the optimum operating temperature was 250°C. The reason for the improved high response is probably due to UV-assisted reaction of photogenerated carries with ethanol. Furthermore, ZnO nanorods were decorated with Pt nanoparticles using a new route, in which ZnO nanorods were surface-functionalized with phosphoethanolamine/platinum complex in solution and then heat-treated. The Pt/ZnO sensor showed a much improved response to ethanol at 150°C under UV light irradiation.

To Japanese Contents　／　To English Contents

---

5.

Tin oxide (SnO₂) has been widely used as a gas sensing material because its electroconductivity is significantly changed under exposure to a reducing gas. The gas sensitivity of SnO₂ increases by the addition of noble metals such as Pt and Pd owning to the activation of their reactivity to flammable gases or an increase in the number of adsorbed oxygen due to the spillover effect. However, the relationship between the gas sensitivity and the effect of noble metals on the reaction mechanism has not been fully understood. In this work, we analyze the ethanol-sensing mechanism of Pt doped-SnO₂ by in situ DRIFT spectroscopy. Pt doped-SnO₂ (1 wt%) was prepared by a liquid-phase synthesis method. The XRD pattern of 1 wt% Pt doped-SnO₂ shows only the pattern of rutile-type SnO₂, indicating that Pt is incorporated into the lattice of SnO₂. The gas sensitivity of 1 wt% Pt doped-SnO₂ is 1.8 times larger than that of non-doped SnO₂ (250℃, 100 ppm EtOH/air). In situ DRIFTS observation revealed that the intermediates of ethanol oxidation change depending on a sensing temperature and Pt doping. The reducibility of 1 wt% Pt doped-SnO₂ is greater than that of non-doped SnO₂, leading to the higher ethanol sensitivity.

To Japanese Contents　／　To English Contents

6.

In order to prevent accidents such as serious breakdown and firing of high-density wiring circuit board, multiple safety countermeasures are required. For this purpose, we had a feasibility study of MOS type sensors through detecting gases, generated from accidentally heated circuit boards. In our GC-MS analysis, small amount of alcohols, amides, fatty acids, ketones and aromatic hydrocarbons were detected when the circuit boards were heated at 250 deg.C. Among the tested sensing materials, Ru/WO₃ based sensor showed mostly uniform sensitivities to 10ppm of the gases, mentioned above. The Ru/WO₃ sensor also showed a reasonable sensitivity to the gases which were generated from heated circuit pattern of 1mm(W)*50mm(L) applying 12A current, and was suggested that the sensor is capable of detecting such abnormal heat at very beginning stage.

To Japanese Contents　／　To English Contents

---

特別講演1

The first commercial battery-powered household gas alarm in the world was launched in 2015 in Japan by cooperation of companies including New Cosmos Electric. For this purpose, we developed tin oxide semiconductor gas sensors by using MEMS technology. On the basis of the success in the MEMS methane sensor, we have applied this technology to detecting various gases such as liquefied petroleum gas, hydrogen, volatile organic compounds. In this work, we present structure and sensing properties of the sensors, focusing on mainly methane sensing. Typical MEMS gas sensors require three or four wires: one pair for heating and the other pair for sensing. Our sensors, however, require only two wires, which are used for both heating and sensing. The unique simple structure, which we refer to as a hot-wire-type one, is preferable for mass-production. An optimized methane sensor with this structure exhibited good sensitivity, high selectivity of methane over interfering gases, and good long-term stability. Low power consumption of the sensor (100 μW) enabled us to commercialize a battery-powered household gas alarm, which is suitable for monitoring gas leak hazards in various locations.

To Japanese Contents　／　To English Contents

---

7.

We are investigating a simple method for simultaneous detection of acetone and NO in exhaled air using the porous glass gas detection chip. In this study, the adsorption of acetone on the NOx detection chip and the reactivity of the porous glass detection chip in a mixed gas atmosphere were evaluated. It was found that the NOx detection chip adsorbed 76% of acetone when exposed to acetone, and then desorbed the acetone when exposed to air. In the mixed atmosphere of acetone and NO, the reactivity of the NOx detection chip was not affected in the acetone concentration range of 0 – 6.9 ppm.

To Japanese Contents　／　To English Contents

---

8.

Development of a hydrogen sensor based on fiber-optic evanescent-wave absorption was tried and characterized. The sensor device composed of silica core (diameter of 200 m) and platinum-doped tungsten trioxide thin film as a clad material was fabricated using sol-gel method. In the presence of hydrogen gas, the strong optical absorption in the near infrared region was observed although the device loss was severe. However, buffer clad of pure tungsten trioxide film was relatively effective to suppress the propagation loss of the sensor device.

To Japanese Contents　／　To English Contents

---

9.

Human exhaled breath contains various volatile organic compounds (VOCs), some of them can be closely related to the particular diseases. Especially, it has been reported that high concentrations of acetone are present in the exhaled air of diabetic patients. Therefore, acetone is expected as a non-invasive biomarker for diabetes. In this study, we developed an acetone analytical chip using 2-nitrophenylhydrazine (2-NPH) and porous glass. Additionally, we considered the possibility of continuous measurement using the analytical chip and an active method. The developed chip exhibited a specific absorption peak at 354 nm. Upon exposure to an acetone atmosphere, new absorption peak was appeared at 446 nm. As a result of repeated exposure to the acetone atmosphere of 2.65 ppm, it was suggested that continuous measurement was possible because it was found that the absorbance at 446 nm cumulatively increased and that the differential absorbance at 446 nm was constant. There is a positive correlation between the acetone concentration and the differential absorbance at 446 nm. Therefore, at a flow velocity of 0.05 L min-1, the acetone concentration (1.19-9.96 ppm) could be calculated in 20 min by using the differential absorbance at 446 nm and the absorbance at 354 nm.

To Japanese Contents　／　To English Contents

---

10.

Praseodymium-doped ceria (Pr_0.1Ce_0.9O₂, PCO) films with columnar structure containing voids were fabricated by pulsed laser deposition (PLD) and integrated into YSZ-based potentiometric gas sensors as sensing electrodes (SEs). Toluene sensing properties of the sensors with PCO film thicknesses of 550, 1100 and 2200 nm, fabricated by controlling the number of PLD shots (x) of 750, 1500 and 3000 respectively, were examined over the temperature range of 450‒600°C. The output voltage, E, of all sensors negatively shifted upon exposure to toluene, and the toluene response (ΔE) increased with increasing toluene concentration. ΔE (ca. 50 ppm) of the sensor using the thickest SE (x: 3000) was much larger than the others (x: 750, 1500) at the examined temperatures (450‒600°C). This result may suggest the progress of the electrochemical oxidation reaction at the interface between PCO and a gas phase, in addition to the conventional reaction sites (triple phase boundaries (PCO/YSZ/gas), by referring to the porous and mixed ionic-electronic conductive nature of PCO. It was also found that the number of reaction sites has a great impact in increasing toluene responses of the sensors.

To Japanese Contents　／　To English Contents

---

11.

We investigated the response characteristic of electromotive force to water vapor pressure for hydrogen sensor using protonic ceramics. Hydrogen sensor can measure hydrogen pressure continuously with high accuracy because the electromotive force of protonic ceramics responds only to the hydrogen concentration. When the water vapor pressure was changed in nitrogen air, a clear change in electromotive force was observed. This means that a small amount of hydrogen in nitrogen or air was detected as the amount of water vapor increased due to the equilibrium of water vapor-hydrogen-oxygen. Based on this result, there is a possibility that a solid electrolyte hydrogen sensor can be used for direct water vapor measurement in a high temperature field, which could not be measured with a hygrometer or dew point meter, and for determining the drying of an object even in an environment containing various corrosive gases such as ammonia.

To Japanese Contents　／　To English Contents

---

12.

Solid electrolyte type CO₂ gas sensor was fabricated by applying a trivalent Al³⁺ ion conducting (Al_0.2Zr_0.8)_20/19Nb(PO₄)₃ solid electrolyte with 0.9Na₃Mg(PO₄)(CO₃)–0.1(0.5Li₂CO₃+0.5BaCO₃) as the auxiliary sensing electrode, and their CO₂ gas sensing properties were investigated under humid atmosphere. The sensor with 0.9Na₃Mg(PO₄)(CO₃)–0.1(0.5Li₂CO₃+0.5BaCO₃) auxiliary sensing electrode showed a superior sensing performance of continuous, quantitative and reproducible response with obeying the theoretical Nernst relationship even in humid atmosphere containing 4.2vol% H₂O at 400°C over 110 days.

To Japanese Contents　／　To English Contents

---

13.

NASICON (Na₃Zr₂Si₂PO₁₂)-based solid electrolyte-type gas sensors using various metal oxides-added Pt as a sensing electrode (SE) and a counter Pt electrode (RE), which were denoted as Pt(MO)/Pt-T (MO: Bi₂O₃, Cr₂O₃, CeO₂ (the amount of MO loaded: 15 wt%), T: calcination temperature, 700–900°C), were fabricated, and their CO responses were investigated at 30°C and −10°C in dry air. The Pt(Bi₂O₃)/Pt-T and Pt(Cr₂O₃)/Pt-T sensors positively responded to CO, while the Pt(CeO₂)/Pt-T sensor negatively responded to CO. In addition, the aging treatment (in dry air for 1.0 h and in 3,000 ppm CO balanced with dry air for 0.5 h at 400°C) increased the magnitude of CO responses of the Pt(Bi₂O₃)/Pt-T and Pt(Cr₂O₃)/Pt-T sensors. On the other hand, the aging treatment decreased the magnitude of CO response of the Pt(CeO₂)/Pt-T sensor.

To Japanese Contents　／　To English Contents

---

清山賞受賞講演1

This article describes a brief review of highly sensitive analytical methods with electrochemically activated carbon electrodes developed by author’s team, and then the practical applications of proposed sensing methods to determine inorganic compounds are introduced. The first topic consists of carbon surface terminated with other atoms containing functional groups such as amino group or tightly immobilized electrodeposited platinum nanoparticles on nitrogen-containing functional groups introduced carbon electrode material, which can control electro-catalytic performance, and are applied to measure various electroactive species. The second topic describes electrochemical sensors based on the batch injection coulometry by using our presented electrodes, which exhibited absolute determination of inorganic compounds in practical fields.

To Japanese Contents　／　To English Contents

---

14.

We have developed all-solid-state K ion-selective electrodes by using a cation insertion material placed between the metal substrate and the ion-selective membrane. Prussian blue analogues were employed as insertion materials which allow K+ ions to be reversibly inserted/extracted into/from their crystal structures associated with electrochemical redox reactions. The double-layered electrodes formed on Pt, Pt/cation insertion material/ISM, exhibited an ideal Nernstian response in the range of 10^-5 – 10^-1 mol dm^-3 with high selectivity for targeted ion and good potential stability. Furthermore, the electrodes consisted of multi-walled carbon nanotube (MWCNT) - KFe[Fe(CN)₆] (KFeFe) as cation insertion materials showed smaller polarization than the electrodes with acetylene black- KFeFe. AC impedance analysis of the all-solid-state electrodes also revealed that the MWCNT-KFeFe were capable of reducing the interfacial resistance, which could originate from the high electrical conductivity of MWCNT.

To Japanese Contents　／　To English Contents

---

15.

We propose an all-solid K+-ion selective electrode (K+-ISE)　and an all-solid ionic-liquid-based membrane reference electrode (IL-RE) with the inner solid electrode coated with insertion material paste. The K+-ISE was integrated into a K+ sensor chip with IL-RE for calibration-free measurements. This insertion material paste contains an inorganic insertion material (Na_0.33MnO₂) and a solid electrolyte (β’’-alumina). The inorganic insertion material, Na_0.33MnO₂, in the paste exhibits a redox reaction accompanied by the disinsertion/insertion of Na+ and acts as an ion-to-electron transducer. Furthermore, β’’-alumina in the paste acts as a supply source of Na+ for Na_0.33MnO₂. The insertion material paste stabilizes the phase boundary potential of the inner solid electrode, even if the ion selective membrane and IL membrane contain no inserted ions (Na+). The fabricated K+-ISE and IL-RE exhibited high device-to-device reproducibility, each standard deviation of the potential was ± 1.0 mV (3 sensors) and ± 0.6 mV (8 sensors) respectively. The fabricated K+ sensor chips exhibited a very high device-to-device potential reproducibility of ± 1.3 mV in KCl solutions and ± 2.2 mV even in blood serum samples. This ion sensor chip realized calibration-free measurement as disposable sensors and showed the possibility of facilitating mass production.

To Japanese Contents　／　To English Contents

---

16.

High adsorption affinity of graphene to potassium (K⁺) and sodium (Na⁺) ions is shown by a theoretical study of metal-carbon structures by using first-principles calculations. In order to investigate how the adsorption affinity affects chemical reactions in solution phase, we studied the effect of K⁺ and Na⁺ concentration in electrochemical measurements using monolayer-graphene electrodes. Here we found that both oxidation and reduction current values of ferrocene decreased with increasing K⁺ concentration on monolayer-graphene electrodes, whereas gold and glassy carbon electrodes did not show a dependence on K⁺ concentration. We found that the K⁺ concentration can be quantified by using monolayer-graphene electrodes.

To Japanese Contents　／　To English Contents

---