Metal Supported SOFC Anode Sintering for REDOX Stability
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Solution Overview
Problem
Metal-supported solid oxide fuel cells (SOFCs) face challenges in stability during reduction-oxidation (REDOX) cycles due to the oxidation of nickel in the anode, leading to volume changes and potential cell failure, especially in anode-supported cells, which are prone to catastrophic cracking. Existing methods for sintering anodes in reducing atmospheres can result in poor sintering of nickel-ceria composites, weak necks between particles, and instability.
Innovation Solution
A process involving the application of a green anode layer with nickel oxide and rare earth-doped ceria to a metal foil substrate, followed by prefiring under non-reducing conditions and subsequent firing in a reducing atmosphere with controlled oxygen partial pressure to form a sintered cermet, ensuring nickel is reduced to nickel metal before sintering, thereby reducing volume changes and enhancing stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nickel oxide is sintered in a reducing atmosphere to form metallic nickel, then the anode achieves good electronic conductivity and catalytic activity, but the nickel particles sinter excessively and form weak necks between particles, reducing structural stability
Solution Approach 1:
The patent changes the oxygen partial pressure parameter during sintering to a controlled reducing atmosphere (10^-14 to 10^-22 bar), which allows nickel oxide to reduce to metallic nickel while controlling the extent of sintering. This parameter change enables the formation of strong particle necks while maintaining porosity and preventing excessive grain growth, thereby resolving the contradiction between conductivity and structural stability.
Solution Approach 2:
The patent uses a composite anode structure consisting of nickel-ceria composite material. The ceria component (0.1 to 2.0 weight ratio relative to nickel oxide) forms a stable ceramic matrix that provides structural support and strong bonding, while the reduced nickel particles provide conductivity and catalytic activity. This composite structure resolves the contradiction by having the ceramic phase bear the mechanical load while the metal phase provides electrical function.
2Strength
If the anode is supported by a thick ceramic layer, then mechanical strength is improved, but the cell becomes prone to catastrophic cracking during REDOX cycling due to volume changes
Solution Approach 1:
The patent changes the sintering atmosphere parameter to a controlled reducing environment with specific oxygen partial pressure ranges. This allows the nickel to reduce in a controlled manner that minimizes volume expansion stress, and the ceria matrix to maintain structural integrity throughout the REDOX cycles, preventing catastrophic cracking while maintaining mechanical strength.
Solution Approach 2:
The nickel-ceria composite anode structure provides both mechanical strength and REDOX stability. The ceria ceramic matrix forms a continuous stable framework that resists cracking, while the nickel particles embedded within provide the necessary volume for electrochemical reactions. This composite architecture resolves the contradiction between strength and REDOX reliability.
3Reliability
If nickel oxide is reduced to metallic nickel, then catalytic activity and electronic conductivity are enhanced, but volume increase occurs leading to stresses and potential cell destruction
Solution Approach 1:
The patent controls the oxygen partial pressure during sintering (10^-14 to 10^-22 bar) to achieve partial reduction of nickel oxide. This controlled reduction minimizes the volume expansion that occurs during full reduction, while still providing sufficient metallic nickel for catalytic activity and electronic conductivity. The ceria matrix also accommodates the volume change through its flexible structure, reducing internal stresses.
Solution Approach 2:
The ceria ceramic matrix in the nickel-ceria composite provides a flexible, stress-absorbing framework that accommodates the volume expansion during nickel reduction. The composite structure allows the metal and ceramic phases to work together, with the ceramic bearing the mechanical stress while the metal provides the electrochemical function, thereby resolving the contradiction between performance and stress.
4Ease of manufacture
If conventional sintering methods are used for nickel-ceria composites, then processing is simplified, but poor sintering occurs with weak necks between particles and reduced stability
Solution Approach 1:
The patent modifies the sintering process by implementing a two-stage approach: first sintering the nickel oxide and ceria together in air or oxygen to form strong ceramic bonds, then performing a controlled reduction in a reducing atmosphere to convert nickel oxide to metallic nickel. This parameter change in the sintering schedule achieves both strong particle necks and high stability without complicating the overall manufacturing process.
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 process results in a highly robust SOFC that can withstand hundreds of high-temperature fuel interruptions without significant performance degradation, with improved sintering of nickel and ceria, reducing the risk of cracking and delamination, and maintaining structural integrity during REDOX cycles.
Implementation Method 1
firing the composite in a reducing atmosphere to form a sintered cermet; wherein the atmosphere comprises an oxygen source; wherein an oxygen partial pressure in the reducing atmosphere of step c) is in the range 10-14 to 10-22 bar
Implementation Method 2
firing the composite in a reducing atmosphere to form a sintered cermet
Implementation Method 3
an oxygen partial pressure in the reducing atmosphere of step c) is in the range 10-14 to 10-22 bar
Data Source
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AI summary
A process for forming a metal supported solid oxide fuel cell, the process comprising the steps of: a) applying a green anode layer including nickel oxide and a rare earth-doped ceria to a metal substrate; b) prefiring the anode layer under non-reducing conditions to form a composite; c) firing the composite in a reducing atmosphere to form a sintered cermet; d) providing an electrolyte; and e) providing a cathode; wherein the reducing atmosphere comprises an oxygen source, a metal supported solid oxide fuel cell formed during this process, fuel cell stacks and the use of these fuel cells.