Iron Redox Flow Battery Rebalancing Cell for In Situ pH Control
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Solution Overview
Problem
All-iron redox flow batteries face issues with electrolyte imbalance due to hydrogen generation during charging, leading to pH increase and precipitation of iron compounds, which reduces efficiency and causes downtime due to the need for additional fluids and separate acids for pH control.
Innovation Solution
Incorporation of a rebalancing cell with a third electrolyte tank and a monitoring system to manage electrolyte pH and balance state of charge using hydrogen gas, allowing for in situ pH adjustment and electrolyte rebalancing without additional acids, thus maintaining optimal operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If acid is titrated into the negative electrolyte to control pH, then pH control is achieved, but additional fluid is required and significant downtime is needed
Solution Approach 1:
The system uses the hydrogen gas already generated during battery charging to produce acid in situ within the electrolyte solution. The hydrogen evolution reaction during charging creates H2 bubbles that dissolve to form H3O+, automatically providing the acid needed for pH control without external intervention. This self-service mechanism eliminates the need for separate acid titration processes and associated downtime.
Solution Approach 2:
Hydrogen gas acts as an intermediary substance that converts the charging process byproduct into a useful component. The H2 generated during charging serves as a mediator that, when dissolved in the electrolyte, forms H3+ ions that counterbalance the pH increase caused by charging, thereby controlling pH without requiring external acid addition.
2Ease of manufacture
If acid is used to flush the iron battery cells to remove deposited Fe(OH)3, then cleaning is achieved, but a separate liquid is required
Solution Approach 1:
The system generates cleaning acid in situ using the hydrogen gas produced during normal charging operations. This self-produced acid serves dual purposes: pH control and cell cleaning to remove Fe(OH)3 deposits. The electrolyte solution itself becomes the cleaning agent, eliminating the need for separate flushing liquids and reducing overall fluid requirements.
Solution Approach 2:
The patent combines multiple functions into a single substance: the electrolyte solution simultaneously serves as the operating medium, pH buffer, and cleaning agent. By generating H3O+ in situ from hydrogen evolution, the same electrolyte that conducts ions also provides acid for dissolving Fe(OH)3 deposits, merging cleaning functionality with the base electrolyte solution.
3Productivity
If hydrogen gas is generated during charging, then charging process occurs, but electrolyte imbalance and pH increase result
Solution Approach 1:
The patent converts the harmful effect of hydrogen gas evolution (which causes pH increase and electrolyte imbalance) into a beneficial effect. The H2 gas that would normally be a waste product or nuisance is instead utilized to generate H3O+ ions in situ, which counterbalance the pH increase and restore electrolyte balance. This transforms a harmful byproduct into a useful component for maintaining system stability.
Solution Approach 2:
The system implements a feedback mechanism where the hydrogen gas produced during charging is detected and utilized to adjust the electrolyte composition. The H2 evolution serves as an indicator of charging progress, and the resulting H3O+ formation provides automatic feedback to counteract pH changes, creating a self-regulating system that maintains electrolyte balance during charging operations.
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
Enables continuous operation with reduced downtime and improved efficiency by maintaining electrolyte balance and preventing precipitation, extending the battery's lifespan and performance.
Implementation Method 1
The rebalancing cell can be used to transfer protons from the negative rebalancing half-cell to the third electrolyte solution passing through the positive rebalancing half-cell
Implementation Method 2
the negative rebalancing half-cell is configured to receive hydrogen gas from the first electrolyte tank and/or from a separate hydrogen source
Implementation Method 3
an all-iron redox flow battery which has the advantage of being cost efficient due to using only iron in different oxidation states as the electrolyte
Implementation Method 4
During charging of an all-iron redox flow battery, molecular hydrogen H2 is generated from protons H+ on the negative flow half-cell
Data Source
AI summary
An all-iron redox flow battery comprising a first electrolyte tank configured to contain a first electrolyte solution and a second electrolyte tank configured to contain a second electrolyte solution; a flow cell comprising a negative flow half-cell configured for passing through first electrolyte solution and a positive flow half-cell configured for passing through second electrolyte solution; a third electrolyte tank, distinct from the first and second electrolyte tanks, configured to contain a third electrolyte solution, wherein the battery is configured to selectively provide fluid communication of the third electrolyte tank with at least one of the first electrolyte tank and the second electrolyte tank; and a rebalancing cell comprising a negative rebalancing half-cell and a positive rebalancing half-cell, wherein the negative rebalancing half-cell is configured to receive hydrogen gas from the first electrolyte tank and/or from a separate hydrogen source, and wherein the positive rebalancing half-cell is configured for passing through third electrolyte solution, whereby the rebalancing cell is configured to lower a pH of the third electrolyte solution.