Redox Flow Battery Electrolyte Balancing via pH Gradient
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Redox flow batteries face incompatibility issues between iron and sulfur electrolytes, leading to cross-over reactions that result in insoluble solids or gaseous losses, reducing efficiency and rendering the batteries inoperable over time.
Innovation Solution
The use of an intermediator electrolyte solution with a pH of 12 or greater, which mitigates incompatibility by allowing sulfur and iron to precipitate as solid products that can be recovered and reused, maintaining battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If iron and sulfur electrolytes are used in redox flow batteries, then energy storage capacity is improved, but cross-over reactions occur leading to insoluble solids and gaseous losses
Solution Approach 1:
A pH gradient is established across the ion-exchange membrane, with the sulfur electrolyte maintained at high pH (11.5 or greater) and the iron electrolyte at low pH (3 or less). This pH gradient acts as an intermediary barrier that prevents direct contact and reaction between iron and sulfur species, eliminating cross-over reactions and the formation of insoluble solids and gases.
Solution Approach 2:
The patent changes the pH parameter of the electrolytes on either side of the membrane. By maintaining the sulfur electrolyte at pH 11.5 or greater and the iron electrolyte at pH 3 or less, the system creates chemically incompatible conditions that prevent cross-over reactions while allowing ionic conduction through the membrane.
2Use of energy by moving object
If iron and sulfur electrolytes are circulated through the battery, then electrical energy storage is enabled, but precipitate formation occurs in the electrodes
Solution Approach 1:
The pH gradient across the ion-exchange membrane serves as an intermediary that prevents iron and sulfur species from mixing. This eliminates the chemical reaction that would otherwise produce insoluble precipitates in the electrodes, while still enabling the redox reactions necessary for electrical energy storage.
Solution Approach 2:
By controlling the pH parameter differently in each electrolyte (high pH for sulfur, low pH for iron), the system prevents the formation of insoluble compounds while maintaining the electrochemical activity needed for energy storage and release.
3Reliability
If separator layer is used to prevent electrolyte mixing, then cross-over reactions are reduced, but ion transport efficiency decreases
Solution Approach 1:
The patent changes the pH parameter gradient across the separator to resolve the contradiction. The ion-exchange membrane maintains physical separation (ensuring reliability) while the pH gradient optimizes ionic conductivity and reaction kinetics on each side, thereby maintaining high ion transport efficiency despite the presence of the separator.
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 approach enables the effective storage and discharge of electrical energy while preventing cross-over reactions, thereby maintaining the round-trip efficiency and extending the operational life of redox flow batteries.
Implementation Method 1
The separator prevents the electrolytes from freely and rapidly mixing but permits selected ions to pass through to complete the redox reactions
Implementation Method 2
a negative fluid electrolyte (sometimes referred to as the anolyte) is delivered to the negative electrode and a positive fluid electrolyte (sometimes referred to as the catholyte) is delivered to the positive electrode to drive reversible redox reactions between redox pairs. Upon charging, the electrical energy supplied causes a chemical reduction reaction in one electrolyte and an oxidation reaction in the other electrolyte
Implementation Method 3
Sulfur from the polysulfide electrolyte solution in the first electrode of the first cell permeates through the ion-exchange layer of the first cell and precipitates as a solid sulfide product in the second electrode
Implementation Method 4
iron from the iron electrolyte solution in the second electrode of the second cell permeates through the ion-exchange layer of the second cell and precipitates as solid iron product
Data Source
AI summary
A redox flow battery includes first and second cells. Each cell has electrodes and a separator layer arranged between the electrodes. A first circulation loop is fluidly connected with the first electrode of the first cell. A polysulfide electrolyte solution has a pH 11.5 or greater and is contained in the first recirculation loop. A second circulation loop is fluidly connected with the second electrode of the second cell. An iron electrolyte solution has a pH 3 or less and is contained in the second circulation loop. A third circulation loop is fluidly connected with the second electrode of the first cell and the first electrode of the second cell. An intermediator electrolyte solution is contained in the third circulation loop. The cells are operable to undergo reversible reactions to store input electrical energy upon charging and discharge the stored electrical energy upon discharging.