Solid Oxide Fuel Cell Metal Substrate Sintering
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Solution Overview
Problem
Solid oxide fuel cells (SOFCs) with metal substrate-supported cathode-electrolyte-anode units face challenges in achieving mechanical strength, thermal shock resistance, and crack-free, gas-tight electrolyte layers due to high sintering temperatures and differing thermal expansion coefficients, leading to potential distortions and delamination.
Innovation Solution
A method involving wet-chemical application of anode and cathode layers on a porous metallic substrate, with a pre-sintered gas-tight electrolyte layer, followed by heat treatments up to 1250°C and below 1000°C respectively, to ensure strong adhesion and minimize thermal stresses, using intermediate layers to prevent interdiffusion and employing a metallic substrate with a suitable thermal expansion coefficient to maintain stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electrolyte is sintered at high temperatures (1300°C to 1500°C) to ensure gas-tightness, then the gas-tightness of the electrolyte is improved, but the thermal stresses and distortion increase due to different thermal expansion coefficients and shrinkage
Solution Approach 1:
The electrolyte layer is pre-sintered to achieve gas-tightness before being integrated with the metallic substrate and other functional layers. This preliminary sintering action ensures the electrolyte is already densified and gas-tight before undergoing subsequent low-temperature processing, thereby avoiding high-temperature-induced distortion and cracking while maintaining reliable gas-tightness.
2Stability of the object's composition
If the electrolyte layer is made thin to reduce thermal stresses, then the thermal shock resistance is improved, but the gas-tightness becomes more difficult to ensure
Solution Approach 1:
The electrolyte layer is pre-sintered at high temperatures before thinning or integration, ensuring that gas-tightness is achieved while the layer is still relatively thick and less susceptible to stress. After pre-sintering, the electrolyte can be thinner and more flexible, maintaining gas-tightness while improving thermal shock resistance.
3Strength
If intermediate layers are made thin to reduce the number of interfaces and improve strength, then the mechanical strength is improved, but the adhesion between layers becomes more critical and difficult to maintain
Solution Approach 1:
The sintering temperature parameter is changed and reduced for the integration of intermediate layers with the metallic substrate and electrolyte. Instead of using high temperatures that would cause distortion, low-temperature sintering (below 1000°C) is employed after the electrolyte is pre-sintered. This parameter change enables thin intermediate layers to achieve sufficient adhesion while maintaining overall mechanical strength and avoiding thermal stress-related failures.
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 method produces SOFCs with enhanced mechanical strength, thermal shock resistance, and a crack-free, gas-tight electrolyte, ensuring reproducible and distortion-free production, while reducing energy requirements and enabling faster startup due to improved thermal conductivity of the metal substrate.
Implementation Method 1
The organic components contained in the layer forming the anode (e.g. binder, plasticizer, pore-forming agent) are first expelled, which usually takes place until a temperature of approx. 500 °C is reached
Implementation Method 2
This layer is then sintered at higher temperatures, creating a material bond between the substrate and the electrolyte
Implementation Method 3
During a further heat treatment at temperatures below 1000 °C, these layers are sintered and firmly bonded to the electrolyte
Data Source
Figure 1
AI summary
The invention relates to a method for producing solid oxide fuel cells (SOFCs) having a cathode-electrolyte-anode unit borne by a metal substrate. The aim of the invention is to provide solid oxide fuel cells that achieve increased strength, improved temperature cycling resistance, and secure adhesion of the layers forming the cathode-electrolyte-anode unit and that can be reproducibly produced without warping. In the method according to the invention, a layer forming the anode is first applied in a wet chemical process to a surface of a porous metal substrate used as a carrier of the cathode-electrolyte-anode unit. An element which has been sintered in a gas-tight manner in advance and forms the electrolyte is then laid on or applied to said layer forming the anode in a planar manner, and in a first heat treatment up to a maximum temperature of 1250 °C, the organic components contained in the layer forming the anode are expelled, said layer is sintered, and a bond is established between the substrate and the electrolyte. Then a further layer forming the cathode is applied to the electrolyte in a wet chemical process and is sintered in a further heat treatment at temperatures below 1000 °C, and the cathode is bonded to the electrolyte.