Pump Electrode Core-Shell Structure for NOx Sensor
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Solution Overview
Problem
Conventional NOx sensors face challenges in accurately measuring NOx concentration due to variations in oxygen pumping ability between pump cells, leading to unstable sensor quality and reduced measurement accuracy, especially when noble metal powders like Pt and Au are used, which have high catalytic activity affecting oxygen partial pressure control.
Innovation Solution
A pump electrode with a conductive paste formulation that includes a liquid containing Au ions, allowing for a controlled Au abundance ratio of 0.01 to 0.3 on the Pt particle surface, reducing catalytic activity and enhancing selective oxygen decomposition, thereby stabilizing the gas sensor's performance and reducing lot-to-lot variations in oxygen pumping ability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If noble metal powder including Pt and Au is used as pump electrode material, then oxygen pumping ability is improved, but catalytic activity with respect to NOx increases causing decomposition and measurement inaccuracy
Solution Approach 1:
The invention applies local quality by creating a core-shell structure where the inner core (Pt) provides oxygen pumping ability and the outer shell (Au) suppresses catalytic activity toward NOx. This spatial differentiation of material properties allows the electrode to simultaneously achieve high oxygen pumping performance while minimizing unwanted NOx decomposition, directly resolving the technical contradiction between reliability and harmful catalytic effects.
2Productivity
If conventional conductive paste manufacturing method is used, then production efficiency is maintained, but lot-to-lot variation in oxygen pumping ability and interelectrode impedance occurs
Solution Approach 1:
The invention applies preliminary action by pre-forming core-shell structured metal particles before incorporating them into the conductive paste. This preliminary structuring ensures that each particle already possesses the desired Au-Pt configuration with controlled Au abundance ratio (0.05-0.50) on the Pt surface, eliminating lot-to-lot variations during subsequent paste mixing and application processes while maintaining production efficiency.
3Reliability
If high Au abundance ratio is applied on Pt particle surface, then selective oxygen decomposition ability is improved, but interelectrode impedance increases
Solution Approach 1:
The invention applies parameter changes by precisely controlling the Au abundance ratio parameter on the Pt particle surface within the optimal range of 0.05-0.50. This parameter optimization balances two competing requirements: sufficient Au coverage to provide selective oxygen decomposition ability while maintaining enough Pt exposure to ensure adequate electrical conductivity and minimize interelectrode impedance. The specific quantitative range represents the optimized parameter window where both benefits are achieved simultaneously.
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 approach results in a stable and accurate NOx concentration measurement by maintaining a linear relation between NO concentration and pump current, while minimizing interelectrode impedance and catalytic activity, thus enhancing the selective decomposition ability of oxygen and improving overall sensor quality.
Implementation Method 1
it constitutes an electrochemical pump cell for adjusting an oxygen partial pressure in the inner space
Implementation Method 2
there is a linear relation between a current value of a current (NOx current) flowing when an oxygen ion generated due to reduction or decomposition of NOx in a measurement electrode is pumped
Data Source
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AI summary
A gas sensor including a pump electrode having high selective decomposition ability with respect to an oxygen gas, and a method for manufacturing a conductive paste capable of forming such pump electrode stably are provided. When the pump electrode constituting an electrochemical pump cell for adjusting an oxygen partial pressure in an inner space of a gas sensor to measure a concentration of a gas component in a measurement gas by a current-limiting method is formed of a cermet of a noble metal and an oxide having oxygen ion conductivity, the noble metal contains a first noble metal having a catalytic activity, and a second noble metal having a catalytic activity suppressing ability to suppress the catalytic activity of the first noble metal with respect to an oxide gas except for oxygen, and an abundance ratio of the second noble metal with respect to the first noble metal in a particle surface of the first noble metal existing in the pump electrode is to be 0.01 to 0.3.