Electrochemical Cell Stack Sectioning to Reduce Shunt Current
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Solution Overview
Problem
Electrochemical cell stacks face inherent shunt current issues due to electrolyte ducts extending across the stack, causing high resistance and potential differences between cells, leading to significant internal shunt current loss, especially in longer stacks.
Innovation Solution
The electrochemical cell stack is divided into sections by duplicating anolyte and catholyte apertures and ducts, with each section having separate electrolyte flow passages, reducing the voltage across these sections to half the overall stack voltage, and incorporating serpentine flow passages to increase electrical resistance and minimize shunt current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If electrolyte ducts extend across the entire stack, then electrolyte distribution is simplified, but shunt current loss increases significantly
Solution Approach 1:
The stack is divided into multiple sections along the electrolyte flow path, with each section having its own separate electrolyte ducts. This segmentation breaks the continuous electrolyte path that caused high shunt current loss, while still maintaining simplified distribution within each section. The sections are arranged in series, with electrolyte flowing from one section to the next through intermediate channels.
2Speed
If frame thickness is reduced to achieve high linear flow velocity, then cell spacing decreases, but depth available for distribution passages is reduced
Solution Approach 1:
The distribution passages are configured to extend in multiple directions within the frame thickness, utilizing both the horizontal and vertical dimensions. This allows sufficient passage depth to be achieved without increasing overall frame thickness, by optimizing the three-dimensional arrangement of the passages rather than relying solely on increased thickness.
3Reliability
If distribution channels are closed to prevent leakage paths, then hydraulic and electrical current leakage is prevented, but flow resistance may increase
Solution Approach 1:
Sealing elements in the form of flexible membranes or thin film gaskets are used to close the distribution channels at the frame edges. These flexible seals provide effective hydraulic and electrical isolation while maintaining smooth flow transitions into the cell cavities, preventing turbulence and minimizing flow resistance. The seals conform to the frame surfaces, ensuring complete closure of leakage paths.
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
This configuration significantly reduces shunt current loss by halving the voltage across sections, improving the efficiency and reliability of the electrochemical cell stack by minimizing internal resistance and leakage.
Implementation Method 1
incorporating serpentine flow passages to increase electrical resistance and minimize shunt current
Implementation Method 2
electrochemical or electrolytic cells, in particular though not exclusively to a regenerative reduction/oxidation (redox) fuel cell stack
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A cell stack has frames having lines of four apertures (41) at each end. In the stack, the apertures form four ducts at each end of the side of the stack, with the ducts extending from end to end of the stack for electrolyte flow therethrough. The apertures in the transfer frames have no passages connected to them. The eight apertures (41) in the passage frame are surrounded in pairs by four grooves (44) and O-rings (45), dividing them into a pair for anolyte feed, a pair for anolyte return, a pair for catholyte feed and a pair for catholyte return. The stack is divided into opposite end sections (46, 47). Only one of each pair is connected to a local feed or return flow passage, contained within the O-rings. The other is connected in the other section. The anolyte feed and return passages (51,52,55,56) lead from their apertures to respective openings (61) from the side (4) of each passage frame to its plain face (18). Here a distribution rebate (62), with spreading features (63), is provided to distribute / collect electrolyte to the graphite felt in the anolyte half cell. The result is that there is no electrical connection via the electrolyte in the ducts between cells at opposite ends of the stack. The inner ones of the ducts connect the cells at opposite ends of the section 46 and the outer ones the cells at opposite ends of the ducts (47). Thus a shunt current paths still exist, but at only half the voltage to the entire stack.