Spinel Oxide Bonding Agent for SOFC Interconnects
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Solution Overview
Problem
In solid oxide fuel cells (SOFCs), the excessive formation of chromia (Cr2O3) at the interface between the interconnector and the bonding agent increases electrical resistance, reducing the overall SOFC output, necessitating a bonding agent that can be sintered at a relatively low temperature to prevent excessive chromia formation while maintaining high conductivity and bonding strength.
Innovation Solution
A bonding agent with a spinel type transition metal oxide, such as MnCo2O4 or CuMn2O4, is used, featuring a co-continuous structure and spherical particles with exposed crystal surfaces, which is sintered at low temperatures (700-900 °C) to achieve high conductivity and bonding strength, potentially incorporating noble metals like Pt or Ag to reduce electric resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-temperature heat treatment is performed to sinter the bonding agent, then the bonding strength and density are improved, but excessive chromia formation occurs at the interface, increasing electrical resistance
Solution Approach 1:
The patent changes the sintering temperature parameter from conventional high temperatures (above 900°C) to a lower range (700-900°C). This parameter change prevents excessive chromia formation at the interface while still achieving sufficient bonding strength and density through the optimized spinel-type oxide composition and sintering atmosphere control.
2Object-affected harmful factors
If sintering temperature is reduced to prevent excessive chromia formation, then chromia formation is suppressed, but bonding strength and density may be insufficient
Solution Approach 1:
The patent uses composite spinel-type oxide materials with specific compositions (such as Mn-Co-O, Cu-Mn-O systems) that exhibit enhanced sintering performance. These composite materials achieve full densification and high bonding strength at lower sintering temperatures (700-900°C) compared to conventional materials, resolving the contradiction between low-temperature processing and bonding strength requirements.
Solution Approach 2:
In addition to temperature reduction, the patent optimizes other sintering parameters including holding time, atmosphere composition (oxygen partial pressure), and heating rate. These combined parameter changes enable the bonding agent to achieve sufficient density and bonding strength at lower temperatures while controlling chromia formation.
3Reliability
If Pt material is used as bonding agent, then electrical conductivity is high, but cost is expensive
Solution Approach 1:
The patent replaces expensive Pt (precious metal) bonding agents with cost-effective spinel-type oxide ceramics (such as MnCo2O4, CuMn2O4). These ceramic materials provide sufficient electrical conductivity for the application while dramatically reducing material cost, embodying the principle of substituting expensive materials with cheaper alternatives that meet performance requirements.
Solution Approach 2:
The patent develops composite ceramic bonding agents with optimized compositions that balance electrical conductivity, bonding strength, and cost. By adjusting the stoichiometry and doping elements in the spinel structure, the material achieves adequate electrical conductivity for SOFC interconnector bonding without requiring precious metals.
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 bonding agent effectively connects conductive members with high conductivity and strong bonding, even at low sintering temperatures, thereby enhancing the SOFC's output by minimizing excessive chromia formation and maintaining low electric resistance.
Implementation Method 1
a paste is sintered with a paste, which is a precursor of the bonding agent, being interposed between the bonding portion of the air electrode and the bonding portion of the interconnector. Thus, the air electrode and the interconnector are bonded and electrically connected by the bonding agent that is a sintered body.
Implementation Method 2
The ferrite SUS material is generally used in a state in which a uniform chromia (Cr2O3) film is formed on the surface with a preliminary oxidation process.
Implementation Method 3
the bonding agent that is a sintered body... electrically connected by the bonding agent... gives high conductivity (gives small electric resistance)
Data Source
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AI summary
Powders of respective metal elements (Mn, Co) constituting a transition metal oxide (MnCo2O4) having a spinel type crystal structure are used as a starting material. A paste containing the mixture of the powders is interposed between an air electrode and an interconnector, and with this state, a sintering is performed, whereby a bonding agent according to the present invention can be obtained. This bonding agent has a "co-continuous structure". In the "co-continuous structure", a thickness of an arm portion that links many base portions to one another is 0.3 to 2.5 µm. The bonding agent includes a spherical particle in which plural crystal faces are exposed to the surface, the particle having a side with a length of 1 µm or more, among the plural sides constituting the outline of the crystal face. The diameter of the particle is 5 to 80 µm.