Pt-Rh Sensor Electrode Gradient for NOx Measurement
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Solution Overview
Problem
Existing NOx sensors face challenges in minimizing the change rate of oxygen ion current and shortening the activation time, as they rely on a constant Pt to Rh ratio in the Pt-Rh alloy, which can lead to prolonged activation times and decreased measurement accuracy due to excessive Rh content causing oxidization and low NOx activity.
Innovation Solution
A NOx sensor design with a Pt-Rh alloy where the mass ratio of Pt to Rh is 70:30 to 35:65, and the Rh percentage in the surface layer is higher than in the whole sensor electrode by 4 to 10 atomic percentage, along with the inclusion of ZrO2 and Y2O3, to enhance NOx decomposition and reduce current change rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Rh content in the Pt-Rh alloy is increased to reduce oxidization, then the resistance to oxidization is improved, but the activation time is prolonged and NOx activity decreases
Solution Approach 1:
The patent applies local quality by creating a surface layer with different composition than the bulk material. The surface layer contains 5-15 mass% Rh (for oxidization resistance) while the bulk contains 20-40 mass% Rh (for NOx activity and fast activation). This gradient structure allows each region to optimize its function locally.
Solution Approach 2:
The patent uses composite materials by combining Pt-Rh alloy with a surface layer having distinct composition. The composite structure consists of the bulk Pt-Rh alloy matrix and the enriched surface layer, where each component contributes different properties: bulk provides structural stability and catalytic activity, while surface layer provides oxidization resistance.
2Productivity
If the Rh content in the Pt-Rh alloy is increased to enhance NOx decomposition ability, then the NOx activity is improved, but the change rate of oxygen ion current increases
Solution Approach 1:
The patent applies local quality by creating a surface layer with different composition than the bulk material. The surface layer contains 5-15 mass% Rh (for oxidization resistance) while the bulk contains 20-40 mass% Rh (for NOx activity and fast activation). This gradient structure allows each region to optimize its function locally.
Solution Approach 2:
The patent uses composite materials by combining Pt-Rh alloy with a surface layer having distinct composition. The composite structure consists of the bulk Pt-Rh alloy matrix and the enriched surface layer, where each component contributes different properties: bulk provides structural stability and catalytic activity, while surface layer provides oxidization resistance.
3Ease of manufacture
If a constant Pt to Rh ratio is used throughout the electrode, then the manufacturing is simplified, but the performance (activation time and current stability) is compromised
Solution Approach 1:
The patent applies local quality by creating a surface layer with different composition than the bulk material. The surface layer contains 5-15 mass% Rh (for oxidization resistance) while the bulk contains 20-40 mass% Rh (for NOx activity and fast activation). This gradient structure allows each region to optimize its function locally.
Solution Approach 2:
The patent applies parameter changes by varying the Rh concentration parameter through the material depth. The composition parameter changes from 5-15 mass% Rh at the surface to 20-40 mass% Rh in the bulk, creating a gradient that optimizes both surface stability and bulk catalytic performance.
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 design effectively decreases the oxygen ion current change rate and shortens the activation time, ensuring stable and accurate NOx measurement by optimizing the Pt to Rh ratio and incorporating ZrO2 and Y2O3, which facilitates better NOx decomposition and conductivity.
Implementation Method 1
The metallic component of the sensor electrode is a Pt—Rh alloy... effectively decreases the oxygen ion current change rate and shortens the activation time, ensuring stable and accurate NOx measurement by optimizing the Pt to Rh ratio and incorporating ZrO2 and Y2O3, which facilitates better NOx decomposition
Implementation Method 2
one or a plurality of solid electrolyte bodies (2) which have oxygen ion conductivity... an oxygen ion current flowing between the sensor electrode and the reference electrode is maintained nearly constant
Implementation Method 3
a pump electrode (21) which is disposed on a surface (201) of the solid electrolyte body which is exposed to measurement gas (G) containing oxygen, the pump electrode being used to regulate an oxygen concentration in said measurement gas
Data Source
AI summary
A NOx sensor is provided which decreases a change rate of an oxygen ion current in a sensor electrode and shortens an activation time of the sensor electrode. The NOx sensor is equipped with a solid electrolyte body, a pump electrode working to regulate an oxygen concentration in measurement gas G, and a sensor electrode working to measure the concentration of NOx in the measurement gas G. A metallic component of the sensor electrode is a Pt—Rh alloy. The mass ratio of Pt to Rh in the whole of the sensor electrode is Pt:Rh=70:30 to 35:65. The percentage of Rh in the Pt—Rh alloy in a surface layer of the sensor electrode is higher than that in the whole of the sensor electrode by an atomic composition percentage of 4 to 10 atom %.