Multi-Chamber Gas Sensor for Reliable H2O and CO2 Measurement
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Solution Overview
Problem
Existing gas sensors face issues with cracking and blackening of sensor elements and evaporation of Au from electrodes due to high applied voltages and temperatures, leading to reduced long-term reliability and sensitivity when measuring water vapor and carbon dioxide concentrations.
Innovation Solution
A multi-gas sensor with a specific electrode configuration and temperature gradient, using a Pt-Au alloy for selective oxidation, and controlled oxygen pumping to prevent decomposition of gases, ensuring stable operation and accurate concentration measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high applied voltage is used to reduce H2O and CO2 in the first internal space, then the reduction of water vapor and carbon dioxide is improved, but the sensor element is cracked and blackened leading to reduced reliability
Solution Approach 1:
The sensor divides the reduction process into two separate internal spaces: the first internal space reduces H2O to H2, and the second internal space reduces CO2 to CO. This segmentation allows each space to operate under optimized conditions without requiring excessively high voltages that would damage the sensor element, thereby resolving the contradiction between measurement precision and reliability.
Solution Approach 2:
The patent introduces an intermediate step where H2O is first reduced to H2 in the first internal space, and then H2 is oxidized back to H2O in the third internal space. This intermediary process allows for indirect measurement of H2O concentration without directly reducing H2O at high voltages that would cause sensor element damage, thus maintaining both precision and reliability.
2Measurement precision
If high temperature is maintained at the pump electrode to reduce H2O and CO2, then the reduction efficiency is improved, but the sensor element is cracked and blackened reducing reliability
Solution Approach 1:
The sensor separates the reduction of H2O and CO2 into different internal spaces with different temperature requirements. The first internal space operates at a lower temperature for H2O reduction, while the second internal space handles CO2 reduction. This segmentation allows efficient reduction without subjecting the entire sensor element to excessively high temperatures that would cause cracking and blackening.
Solution Approach 2:
Different regions of the sensor element are maintained at different temperatures optimized for their specific functions. The first internal space is maintained at a temperature suitable for H2O reduction, while the second internal space is maintained at a temperature suitable for CO2 reduction. This local quality approach ensures high reduction efficiency in each region without compromising the overall sensor element integrity.
3Measurement precision
If Au alloy electrode is used for selective H2 oxidation, then the selective oxidation property is improved, but Au evaporates during long-term use changing sensitivity
Solution Approach 1:
The patent replaces the expensive and unstable Au-based electrode with a Pt-based electrode that does not evaporate during long-term use. While Pt is also a noble metal, it has significantly lower vapor pressure at operating temperatures compared to Au, ensuring long-term stability of sensitivity. This substitution maintains selective H2 oxidation capability while eliminating the evaporation problem.
Solution Approach 2:
The patent changes the material parameter of the electrode from Au-based to Pt-based, which fundamentally alters the evaporation characteristics. Pt has a much lower vapor pressure at the operating temperatures of the sensor, thereby preventing the evaporation issue that plagues Au-based electrodes during long-term use while maintaining the selective oxidation function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The sensor achieves long-term reliability by preventing cracking and blackening of the sensor element and suppressing Au evaporation, while maintaining accurate measurement of water vapor and carbon dioxide concentrations.
Implementation Method 1
a sensor element having a structure formed of an oxygen-ion conductive solid electrolyte
Implementation Method 2
a first measurement pump cell including the first measurement electrode, the out-of-space pump electrode, and a portion of the solid electrolyte present between the first measurement electrode and the out-of-space pump electrode
Implementation Method 3
a heater heating the sensor element, the heater heats the sensor element so that a temperature is highest near the first adjustment electrode in the internal chamber and decreases with increasing distance from the first adjustment electrode
Implementation Method 4
a first adjustment pump cell including the first adjustment electrode, an out-of-space pump electrode provided at a location other than a location in the internal chamber, and a portion of the solid electrolyte present between the first adjustment electrode and the out-of-space pump electrode
Implementation Method 5
the first measurement pump cell pumps oxygen into the internal chamber to selectively oxidize, near the first measurement electrode, hydrogen generated by reduction of water vapor
Data Source
AI summary
A sensor element includes: first to third chambers communicating sequentially from a gas inlet; and a heater performing heating so that a temperature is highest near the first chamber, a first adjustment pump cell pumps oxygen out of a measurement gas introduced into the first chamber to the extent that H2O and CO2 are not decomposed, a second adjustment pump cell pumps out oxygen from the second chamber so that all H2O and CO2 are reduced, a first measurement pump cell pumps oxygen into the third chamber to selectively oxidize H2 near the first measurement electrode, a second measurement pump cell pumps oxygen into the third chamber to oxidize H2 and CO near the second measurement electrode, concentrations of H2O and CO2 are identified from values of currents generated by pumping-in by these measurement pump cells.