Gas Sensor Element with Segmented Pump Cells for NOx Detection
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Solution Overview
Problem
Conventional gas sensors face challenges in accurately measuring a wide concentration range of target gases, such as NOx, due to deterioration in detection accuracy over time and difficulties in controlling diffusion resistance during production.
Innovation Solution
The sensor element incorporates a target-gas-decomposing pump cell and a residual-oxygen-measuring pump cell, where the target-gas-decomposing pump electrode has catalytic activity to decompose the target gas, and the residual-oxygen-measuring electrode only has catalytic activity for oxygen, allowing for accurate measurement of a wide concentration range of the target gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pump electrode containing Au is used to prevent decomposition of target gas, then measurement precision is improved initially, but reliability deteriorates due to Au evaporation and adhesion to measurement electrode over time
Solution Approach 1:
The sensor element is divided into functionally distinct regions: a target-gas-decomposing pump cell with a catalyst electrode for decomposing target gas, and a residual-oxygen-measuring pump cell with a different electrode for measuring residual oxygen. This segmentation prevents the measurement electrode from being contaminated by evaporated Au from the pump electrode, thereby maintaining both measurement precision and reliability over time.
Solution Approach 2:
A solid electrolyte layer acts as an intermediary barrier between the target-gas-decomposing pump electrode and the residual-oxygen-measuring electrode. This intermediary prevents direct contact and contamination between the two electrode regions, protecting the measurement electrode from Au adhesion while allowing ionic conduction for measurement functionality.
2Measurement precision
If diffusion resistance is increased to measure high concentration of target gas, then measurement precision for high concentration is improved, but manufacturing precision becomes difficult to control during production
Solution Approach 1:
Instead of relying on diffusion resistance control, the invention changes the operating parameters by using a target-gas-decomposing pump cell that actively decomposes the target gas and removes oxygen. This allows accurate measurement across a wide concentration range without requiring precise control of diffusion resistance during manufacturing.
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
This configuration suppresses deterioration in detection accuracy over time, maintains high measurement accuracy for both high and low concentrations of NOx, and improves the durability of the gas sensor.
Implementation Method 1
a base part in an elongated plate shape, including a plurality of oxygen-ion-conductive solid electrolyte layers stacked
Implementation Method 2
the target-gas-decomposing pump electrode has catalytic activity to decompose the target gas
Implementation Method 3
the residual-oxygen-measuring electrode only has catalytic activity for oxygen, allowing for accurate measurement of a wide concentration range of the target gas
Data Source
AI summary
A sensor element includes a base part including a plurality of oxygen-ion-conductive solid electrolyte layers stacked; a measurement-object gas flow part for introduction and flow of a measurement-object gas through one end part in a longitudinal direction of the base part; a main pump cell including an inner main pump electrode disposed on an inner surface of the measurement-object gas flow part, and an outer pump electrode; a target-gas-decomposing pump cell including a target-gas-decomposing pump electrode disposed at a position farther from the one end part than the inner main pump electrode, and an outer pump electrode; a residual-oxygen-measuring pump cell including a residual-oxygen-measuring electrode disposed at a position farther from the one end part than the inner main pump electrode, and an outer pump electrode; and a reference electrode. The target-gas-decomposing pump electrode comprises a metal material that has catalytic activity of decomposing a target gas to be measured.