Solid Alkali Ion Membrane Protection via Catholyte Halides
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Solution Overview
Problem
Solid alkali ion conductive electrolyte membranes in electrochemical cells are susceptible to degradation by dissolution, especially in high pH environments, leading to reduced efficiency and shortened lifespan due to chemical reactions with catholyte solutions.
Innovation Solution
Incorporating concentrated halide ions, polyhalide ions, pseudohalide ions, or sulfide ions in the catholyte solution at concentrations greater than 3M, up to saturation, to protect the membrane from degradation by dissolution, maintaining structural stability and alkali ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solid alkali ion conductive electrolyte membranes are used in electrochemical cells with aqueous catholyte solutions, then ion selectivity and water impermeability are improved, but membrane degradation by dissolution occurs at high pH
Solution Approach 1:
A coating layer comprising metal fluoride, metal oxide, or metal hydroxide is applied to the surface of the solid alkali ion conductive electrolyte membrane. This coating layer acts as an intermediary barrier between the membrane and the high pH aqueous catholyte solution, preventing direct contact and chemical dissolution while allowing alkali ion transport to continue.
Solution Approach 2:
The surface chemistry and composition of the membrane are modified by applying a coating layer with different chemical properties (metal fluoride, oxide, or hydroxide). This changes the membrane's resistance to alkaline dissolution without compromising its bulk ion conductivity, enabling operation in high pH environments.
2Productivity
If high pH catholyte solutions are used in electrochemical cells, then chemical reactions at the cathode are enhanced, but alkali ion conductive ceramic membranes structurally degrade by dissolution
Solution Approach 1:
The coating layer serves as a protective intermediary that allows the system to maintain high pH catholyte conditions for enhanced cathode reactions while preventing the membrane structure from dissolving in the alkaline environment.
Solution Approach 2:
The membrane system becomes a composite structure combining the bulk solid alkali ion conductive ceramic material with a surface coating layer of metal fluoride, oxide, or hydroxide. This composite structure provides both the ion conductivity of the ceramic and the chemical stability of the coating in high pH 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 presence of these ions significantly reduces membrane degradation, ensuring prolonged stability and efficiency of the alkali ion conductive electrolyte membrane, even at elevated temperatures, as demonstrated by reduced weight loss and maintained cell performance over multiple charge/discharge cycles.
Implementation Method 1
Solid alkali ion conductive electrolyte membranes are used in electrochemical cells for various reasons, including, but not limited to, being ion conductive
Implementation Method 2
Incorporating concentrated halide ions, polyhalide ions, pseudohalide ions, or sulfide ions in the catholyte solution at concentrations greater than 3M, up to saturation, to protect the membrane from degradation by dissolution
Data Source
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AI summary
The present invention provides an electrochemical cell (210) having an negative electrode compartment (215) and a positive electrode compartment (225). A solid alkali ion conductive electrolyte membrane (240) is positioned between the negative electrode compartment (215) and the positive electrode compartment (225). A catholyte solution in the positive electrode compartment (225) includes a halide ion or pseudohalide ion concentration greater than 3M, which provides degradation protection to the alkali ion conductive electrolyte membrane (240). The halide ion or pseudohalide ion is selected from chloride, bromide, iodide, azide, thiocyanate, and cyanide. In some embodiments, the electrochemical cell (210) is a molten sodium rechargeable cell which functions at an operating temperature between about 100°C and about 150°C.