Staged Pump-Cell 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 the sensor element and evaporation of Au from electrodes due to high applied voltages and temperatures, leading to reduced long-term reliability when measuring water vapor (H2O) and carbon dioxide (CO2) concentrations.
Innovation Solution
A multi-gas sensor with a sensor element comprising an oxygen-ion conductive solid electrolyte structure, including an adjustment pump cell, first and second measurement pump cells, and a heater that maintains a temperature gradient, allowing for controlled pumping and oxidation of gases to measure H2O and CO2 concentrations without decomposition, while suppressing high voltages and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high applied voltage is used in the pump cell for the first internal space 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 gas sensor divides the reduction process into two separate stages: the first measurement pump cell performs partial reduction of H2O and CO2, and the second measurement pump cell completes the reduction. This segmentation allows each cell to operate at lower, safer voltages while collectively achieving the required reduction efficiency, preventing sensor element damage.
Solution Approach 2:
The first measurement pump cell acts as an intermediary that performs initial reduction of H2O and CO2 to H2 and CO, which are then further reduced in the second measurement pump cell. This intermediate step distributes the electrochemical stress across two cells, preventing the high voltage damage that would occur in a single-cell system.
2Productivity
If high temperature is maintained in the pump electrode to reduce H2O and CO2, then the reduction reaction efficiency is improved, but the solid electrolyte ceramics are reduced causing cracking and blackening
Solution Approach 1:
The high-temperature reduction process is divided into two sequential stages in separate measurement pump cells. Each cell operates at a moderate temperature sufficient for its specific reduction task, avoiding the need to maintain excessively high temperatures throughout the entire system that would damage the solid electrolyte ceramics.
Solution Approach 2:
The system changes operational parameters (temperature and voltage) for each measurement pump cell based on its specific function. The first measurement pump cell operates at parameters optimized for partial reduction, while the second operates at parameters optimized for complete reduction, allowing efficient operation without exceeding the thermal stability limits of the solid electrolyte materials.
3Measurement precision
If Au-based electrode material is used to improve selective H2 oxidation property, then the oxidation selectivity is improved, but Au evaporates during long-term use changing sensitivity
Solution Approach 1:
The patent extracts the Au-based electrode material from the first measurement pump cell environment where it would be exposed to high temperatures and oxygen that cause evaporation. Instead, Au-based material is used only in the second measurement pump cell where conditions are more favorable for long-term stability, while maintaining H2 oxidation capability through alternative materials or conditions in the first cell.
Solution Approach 2:
Different electrode materials are used in different measurement pump cells based on local requirements. The first measurement pump cell uses materials optimized for initial reduction, while the second measurement pump cell uses Au-based materials for selective H2 oxidation under more stable conditions, achieving both selectivity and long-term reliability in their respective locations.
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 solution enhances long-term reliability by preventing cracking and blackening of the sensor element and reducing electrode evaporation, enabling accurate and simultaneous measurement of H2O and CO2 concentrations over extended periods.
Implementation Method 1
a sensor element having a structure formed of an oxygen-ion conductive solid electrolyte
Implementation Method 2
a heater heating the sensor element, the heater heats the sensor element so that a temperature is highest near the adjustment electrode in the internal chamber and decreases with increasing distance from the adjustment electrode
Implementation Method 3
an adjustment pump cell including the adjustment electrode, an out-of-space pump electrode provided at a location other than a location in the internal chamber... a first measurement pump cell including the first measurement electrode, the out-of-space pump electrode... a second measurement pump cell including the second measurement electrode, the out-of-space pump electrode
Implementation Method 4
the second measurement pump cell pumps oxygen into the internal chamber to selectively oxidize hydrogen generated by reduction of water vapor
Implementation Method 5
Concentrations of H2O and CO2 in the measurement gas are respectively measured based on magnitudes of pump currents flowing through the first measurement pump cell and the second measurement pump cell when H2 and CO are oxidized
Implementation Method 6
the first measurement pump cell pumps oxygen out of the measurement gas having reached the first measurement electrode so that substantially all water vapor and carbon dioxide contained in the measurement gas of which oxygen has been pumped out by the adjustment pump cell are reduced
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, an 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 first measurement pump cell pumps out oxygen from the second chamber so that all H2O and CO2 contained in the measurement gas are reduced, a second measurement pump cell pumps oxygen into the third chamber to selectively oxidize H2 generated by reduction, a concentration of H2O is identified from a value of a current generated by pumping-in by the second measurement pump cell, and a concentration of CO2 is identified based on the identified concentration of H2O and a value of a current generated by pumping-out by the first measurement pump cell.