Gas Sensor Element Catalyst Trap Layer Hydrogen Oxidation
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Solution Overview
Problem
Gas sensor elements in direct injection gasoline and CNG engines experience output shifts due to differences in diffusion rates of hydrogen and other combustion gases through porous diffusion resistance layers, leading to inaccurate air-fuel ratio detection and catalyst activation issues, especially under unstable combustion conditions and high temperatures.
Innovation Solution
A gas sensor element with a catalyst support trap layer containing platinum, rhodium, and palladium as noble metal catalysts, where palladium is within a specific weight percentage range to prevent cohesion and absorption issues, ensuring stable catalyst performance and quick response capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a porous diffusion resistance layer is used to limit the passage amount of target gases, then the gas sensor can detect air-fuel ratio, but hydrogen gas passes through faster than other combustion gases causing output shift from correct output value
Solution Approach 1:
A catalyst support trap layer is introduced as an intermediary between the porous diffusion resistance layer and the target gas electrode. This layer contains a catalyst that selectively oxidizes hydrogen gas, converting it to water before it reaches the electrode. This mediator prevents hydrogen from directly affecting the measurement, thereby eliminating the output shift while maintaining the ability to detect air-fuel ratio through oxygen concentration measurements.
Solution Approach 2:
The invention changes the chemical state of hydrogen gas by introducing a catalyst that transforms hydrogen (H2) into water (H2O) through oxidation. This parameter change in the chemical composition and reactivity of the gas stream prevents hydrogen from interfering with the electrochemical measurement at the electrode, thereby improving output accuracy.
2Measurement precision
If the diffusion length in the porous diffusion resistance layer is increased to improve air-fuel ratio detection, then the detection capability is enhanced, but the difference in diffusion rate between hydrogen gas and other combustion gases becomes larger causing larger output shift
Solution Approach 1:
The catalyst support trap layer serves as a mediator that addresses the diffusion rate difference problem. By placing the catalyst in this intermediate layer, hydrogen gas is oxidized during its passage regardless of the diffusion length through the porous layer. This ensures that even with increased diffusion length for better detection capability, the hydrogen concentration reaching the electrode remains controlled, preventing output shift.
3Reliability
If noble metal catalyst is used to burn hydrogen gas, then output shift is prevented, but the noble metal particles may cohere under high temperature causing deterioration of catalyst capability
Solution Approach 1:
A porous coating layer is applied over the catalyst support trap layer containing the noble metal particles. This thin film structure physically separates and disperses the catalyst particles, preventing them from cohering together under high temperature conditions. The porous structure allows gas permeability while maintaining particle dispersion, thereby preserving catalyst capability and extending its operational duration.
Solution Approach 2:
The invention creates a composite structure combining the catalyst support material, noble metal catalyst particles, and a porous coating material. This composite architecture provides both the catalytic function for hydrogen oxidation and the structural protection against particle cohering, thereby maintaining both output accuracy and catalyst endurance under high temperature operating conditions.
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 effectively prevents output shifts and maintains catalyst endurance by adequately burning hydrogen gas and preventing cohesion between noble metal particles, ensuring accurate air-fuel ratio detection and rapid catalyst activation.
Implementation Method 1
The catalyst support trap layer is formed on the outer surface of the porous diffusion resistance layer and supports noble metal catalyst. In particular, the noble metal catalyst is made of platinum, rhodium, palladium supported in the catalyst support trap layer
Implementation Method 2
adequately burning hydrogen gas and preventing cohesion between noble metal particles
Implementation Method 3
The porous diffusion resistance layer is capable of limiting the introduction or passage amount of target gases to be measured. Because hydrogen gas has a smaller molecular weight than that of another combustion gas such as oxygen gas in air, the hydrogen gas can arrive at or reach a target gas electrode in the gas sensor element faster than another combustion gas
Data Source
AI summary
A gas sensor element has a solid electrolyte body of oxygen ionic conductivity, a target gas electrode and a reference gas electrode formed on both surfaces of the solid electrolyte body, respectively, a porous diffusion resistance layer, and a catalyst support trap layer. The porous diffusion resistance layer covers the target gas electrode and through which target gases to be measured are passing. The catalyst support trap layer is formed on the outer surface of the porous diffusion resistance layer and supports noble metal catalyst. In the gas sensor element, the noble metal catalyst is made of platinum, rhodium, palladium supported in the catalyst support trap layer. In particular, an addition amount of palladium in the total amount of the noble metal catalyst is within a range of 2 to 65 wt %.