NOx Sensor Outer Pump Electrode Zirconia Composition
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Solution Overview
Problem
NOx sensors experience noise current peaks and reduced detection accuracy when the measurement atmosphere changes from lean to rich due to uneven oxygen adsorption on inner and outer pump electrodes, leading to differences in oxygen partial pressure and electromotive force.
Innovation Solution
The NOx sensor element includes a first pump cell with inner and outer pump electrodes, where the outer pump electrode contains at least 22% by mass of the main component of the solid electrolyte, accelerating its modification and oxygen adsorption, and potentially up to 26%, to equalize oxygen adsorption on both electrodes, reducing noise current and maintaining detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rich aging treatment is performed on the inner pump electrode to increase oxygen adsorption, then the reaction interface amount increases and sensor activation improves, but the outer pump electrode has insufficient oxygen adsorption causing oxygen partial pressure differences between electrodes
Solution Approach 1:
The patent applies different material compositions to different parts of the electrode structure. The outer pump electrode contains 22-40 mass% zirconia to increase its oxygen adsorption capacity specifically, while the inner pump electrode receives the rich aging treatment. This local differentiation of material properties allows each electrode to be optimized for its specific function while working together as a system.
Solution Approach 2:
The patent changes the chemical composition parameter of the outer pump electrode by incorporating a specific amount of zirconia (22-40 mass%). This parameter change increases the oxygen adsorption capacity of the outer electrode, balancing the oxygen partial pressure between the inner and outer electrodes during operation and reducing noise current.
2Measurement precision
If the outer pump electrode contains higher zirconia content (22-40% by mass) to increase oxygen adsorption, then oxygen partial pressure equalization improves and noise current decreases, but electrode material complexity increases
Solution Approach 1:
The outer pump electrode is designed as a composite material containing both noble metal (platinum or rhodium) and zirconia in specific proportions (22-40 mass% zirconia). This composite structure combines the catalytic properties of the noble metal with the oxygen storage capacity of zirconia, achieving improved oxygen adsorption while maintaining electrode functionality.
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 noise current in the first pump cell and maintains detection accuracy by equalizing oxygen adsorption on both electrodes, reducing the electromotive force caused by oxygen partial pressure differences.
Implementation Method 1
accelerating its modification and oxygen adsorption, and potentially up to 26%, to equalize oxygen adsorption on both electrodes
Implementation Method 2
a first pump cell configured to pump out and pump in oxygen in a measurement target gas introduced into a first measurement chamber, to adjust an oxygen concentration in the first measurement chamber
Implementation Method 3
a diffusion resistance portion disposed between outside and the first measurement chamber and configured to adjust a diffusion rate of the measurement target gas introduced into the first measurement chamber
Data Source
AI summary
A NOx sensor element includes: a first pump cell configured to adjust an oxygen concentration in a first measurement chamber; a diffusion resistance portion configured to adjust a diffusion rate of a measurement target gas introduced into the first measurement chamber; and a second pump cell in which a pump current corresponding to a NOx concentration in the measurement target gas after the adjustment of the oxygen concentration, flows. The first pump cell includes: a first solid electrolyte; an inner pump electrode containing a noble metal, and exposed to the first measurement chamber; and an outer pump electrode containing a noble metal, and disposed outside the first measurement chamber. The outer pump electrode contains not less than 22% by mass of a main component of the first solid electrolyte.