Stability improvement of layered Au,Pt-YSZ mixed-potential gas sensing electrodes by cathodic polarization: Studies by steady state and dynamic electrochemical methods

Zhang, X.; Kohler, Heinz; Schwotzer, Matthias; Guth, U.

doi:10.1016/j.snb.2021.130065

Cited by 8 publications

(5 citation statements)

References 74 publications

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“…Detailed studies of the sensor performance when exposed to ambient air and to model gases like CO admixed with synthetic air over about 100 days revealed clear aging effects, which were mainly observed as sensitivity loss. These instabilities have been indicated to be correlated with changes of the Au-distribution in the AuPt-electrode material with operation time [ 30 ] and are likely attributed to the formation of an additional oxide phase at the metallic parts of the triple-phase-contacts [ 34 ]. By modification of the AuPt-mixed potential electrode material (more homogeneous AuPt-distribution) and careful adjustment of the operation temperature (600 °C), the long-term stability of this type of gas sensor could be substantially enhanced and, with a deeper understanding of the reasons for sensitivity loss, an electrochemical procedure for sensor regeneration by cathodic polarization, possible at the site of installation, could be developed.…”

Section: Methods Of Sensor-based Air Stream Control For Optimization ...mentioning

confidence: 99%

“…In Equation (4), the constants a, b i and c depend on the reaction rates and φ 0 is a constant electric potential that relates to the sensor signal U = φ m − φ ref = 0 at synthetic air exposure, whereas φ ref is the potential of the Pt/YSZ-reference half-cell [ 34 ].…”

Section: Methods Of Sensor-based Air Stream Control For Optimization ...mentioning

confidence: 99%

“…By modification of the AuPt-mixed potential electrode material (more homogeneous AuPt-distribution) and careful adjustment of the operation temperature (600 • C), the long-term stability of this type of gas sensor could be substantially enhanced and, with a deeper understanding of the reasons for sensitivity loss, an electrochemical procedure for sensor regeneration by cathodic polarization, possible at the site of installation, could be developed. Moreover, sensitivity loss due to aging effects was indicated by a clear increase in the electrode impedance [34]. This allows a check of the sensor performance in predefined time intervals and regeneration on demand [27].…”

Section: Aspects Of Continous In Situ Flue Gas Analysis By Gas Sensorsmentioning

confidence: 99%

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Extensive Gaseous Emissions Reduction of Firewood-Fueled Low Power Fireplaces by a Gas Sensor Based Advanced Combustion Airflow Control System and Catalytic Post-Oxidation

Zhang,

Ojha,

Bichlmaier

et al. 2023

Sensors

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In view of the tremendous emissions of toxic gases and particulate matter (PM) by low-power firewood-fueled fireplaces, there is an urgent need for effective measures to lower emissions to keep this renewable and economical source for private home heating available in the future. For this purpose, an advanced combustion air control system was developed and tested on a commercial fireplace (HKD7, Bunner GmbH, Eggenfelden, Germany), complemented with a commercial oxidation catalyst (EmTechEngineering GmbH, Leipzig, Germany) placed in the post-combustion zone. Combustion air stream control of the wood-log charge combustion was realized by five different control algorithms to describe all situations of combustion properly. These control algorithms are based on the signals of commercial sensors representing catalyst temperature (thermocouple), residual oxygen concentration (LSU 4.9, Bosch GmbH, Gerlingen, Germany) and CO/HC-content in the exhaust (LH-sensor, Lamtec Mess- und Regeltechnik für Feuerungen GmbH & Co. KG, Walldorf (Germany)). The actual flows of the combustion air streams, as calculated for the primary and secondary combustion zone, are adjusted by motor-driven shutters and commercial air mass flow sensors (HFM7, Bosch GmbH, Gerlingen, Germany) in separate feedback control loops. For the first time, the residual CO/HC-content (CO, methane, formaldehyde, etc.) in the flue gas is in-situ monitored with a long-term stable AuPt/YSZ/Pt mixed potential high-temperature gas sensor, which allows continuous estimation of the flue gas quality with an accuracy of about ±10%. This parameter is not only an essential input for advanced combustion air stream control but also provides monitoring of the actual combustion quality and logging of this value over a whole heating period. By many firing experiments in the laboratory and by field tests over four months, it could be demonstrated that with this long-term stable and advanced automated firing system, depression of the gaseous emissions by about 90% related to manually operated fireplaces without catalyst could be achieved. In addition, preliminary investigations at a firing appliance complemented by an electrostatic precipitator yielded PM emission depression between 70% and 90%, depending on the firewood load.

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Section: Methods Of Sensor-based Air Stream Control For Optimization ...mentioning

confidence: 99%

Section: Methods Of Sensor-based Air Stream Control For Optimization ...mentioning

confidence: 99%

Section: Aspects Of Continous In Situ Flue Gas Analysis By Gas Sensorsmentioning

confidence: 99%

See 1 more Smart Citation

Extensive Gaseous Emissions Reduction of Firewood-Fueled Low Power Fireplaces by a Gas Sensor Based Advanced Combustion Airflow Control System and Catalytic Post-Oxidation

Zhang,

Ojha,

Bichlmaier

et al. 2023

Sensors

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“…As shown in a typical measurement sequence, the fluctuation of the c(CO) by more than 1% (Figure 8b) is in rather good (reciprocal) coincidence with the variation of the residual oxygen concentration represented by Ip over time (Figure 8a) in both settings. This is particularly demonstrated by the variation of the signal of the second, non-Nernst mixed-potential electrochemical cell [20] realized by the KS1D high-temperature combined CO/HC-oxygen sensor, which represents the combustible gas components (mainly H 2, CH 4 and CO) in a better resolution over time. These CO/HC fluctuations are observed under conditions of constant synthetic air flow, which was set to the λ = 1-condition at minute 94 (setting 1, Figure 8c).…”

Section: Evaluation Of the Tar Monitoring Setup With The Real Syngas ...mentioning

confidence: 99%

Gasification of Biomass: The Very Sensitive Monitoring of Tar in Syngas by the Determination of the Oxygen Demand—A Proof of Concept

et al. 2022

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A novel method for quasi-continuous tar monitoring in hot syngas from biomass gasification is reported. A very small syngas stream is extracted from the gasifier output, and the oxygen demand for tar combustion is determined by a well-defined dosage of synthetic air. Assuming the total oxidation of all of the combustible components at the Pt-electrode of a lambda-probe, the difference of the residual oxygen concentrations from successive operations with and without tar condensation represents the oxygen demand. From experiments in the laboratory with H2/N2/naphthalene model syngas, the linear sensitivity and a lower detection limit of about 70 ± 5 mg/m3 was estimated, and a very good long-term stability can be expected. This extremely sensitive and robust monitoring concept was evaluated further by the extraction of a small, constant flow of hot syngas as a sample (9 L/h) using a Laval nozzle combined with a metallic filter (a sintered metal plate (pore diameter 10 µm)) and a gas pump (in the cold zone). The first tests in the laboratory of this setup—which is appropriate for field applications—confirmed the excellent analysis results. However, the field tests concerning the monitoring of the tar in syngas from a woodchip-fueled gasifier demonstrated that the determination of the oxygen demand by the successive estimation of the oxygen concentration with/without tar trapping is not possible with enough accuracy due to continuous variation of the syngas composition. A method is proposed for how this constraint can be overcome.

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“…In addition, the sensitivity can be checked in defined time periods of operation by electrochemical impedance spectroscopy (EIS) to the environmental air conditions of the place of operation, and a special strategy has been developed for sensor regeneration in cases of sensitivity loss. More details about this high-temperature mixed-potential gas sensor and its long-term behavior regarding the flue gas of a wood log fueled fireplace are reported in [ 11 ], and basic studies of the mixed-potential generation of Au,Pt-YSZ electrodes and a method of sensitivity check and stability improvement are published in [ 12 , 13 ].…”

Section: Introductionmentioning

confidence: 99%

Application of a Robust Thermoelectric Gas Sensor in Firewood Combustion Exhausts

Hagen

Herrmann

Zhang

et al. 2023

Sensors

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The quality of wood combustion processes can be effectively improved by achieving the automated control of the combustion air feed. For this purpose, continuous flue gas analysis using in situ sensors is essential. Besides the successfully introduced monitoring of the combustion temperature and the residual oxygen concentration, in this study, in addition, a planar gas sensor is suggested that utilizes the thermoelectric principle to measure the exothermic heat generated by the oxidation of unburnt reducing exhaust gas components such as carbon monoxide (CO) and hydrocarbons (CxHy). The robust design made of high-temperature stable materials is tailored to the needs of flue gas analysis and offers numerous optimization options. Sensor signals are compared to flue gas analysis data from FTIR measurements during wood log batch firing. In general, impressive correlations between both data were found. Discrepancies occur during the cold start combustion phase. They can be attributed to changes in the ambient conditions around the sensor housing.

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Stability improvement of layered Au,Pt-YSZ mixed-potential gas sensing electrodes by cathodic polarization: Studies by steady state and dynamic electrochemical methods

Cited by 8 publications

References 74 publications

Extensive Gaseous Emissions Reduction of Firewood-Fueled Low Power Fireplaces by a Gas Sensor Based Advanced Combustion Airflow Control System and Catalytic Post-Oxidation

Extensive Gaseous Emissions Reduction of Firewood-Fueled Low Power Fireplaces by a Gas Sensor Based Advanced Combustion Airflow Control System and Catalytic Post-Oxidation

Gasification of Biomass: The Very Sensitive Monitoring of Tar in Syngas by the Determination of the Oxygen Demand—A Proof of Concept

Application of a Robust Thermoelectric Gas Sensor in Firewood Combustion Exhausts

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