Redox Flow Battery Mediator for Cr2O7^2- Regeneration
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Solution Overview
Problem
Redox flow batteries face limitations in energy and power density due to the use of oxidants that undergo 1 or 2 electron reductions or have low solubility, leading to large battery sizes and high costs, with previous attempts at using Cr2O7^2- being inefficient due to irreversible reactions at known electrode catalysts.
Innovation Solution
The introduction of an electrochemically reversible electron mediator that heterogeneously oxidizes Cr3+ back to Cr2O7^2- using an EC catalytic mechanism, allowing for the reversible use of Cr2O7^2- in redox flow batteries, which overcomes the issue of irreversible reactions and enhances energy and power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Cr2O7^2- is used as oxidant in redox flow battery, then energy density and power density are improved, but irreversible reactions occur at electrode catalysts preventing rechargeability
Solution Approach 1:
The patent introduces a soluble electron mediator that acts as an intermediary between the Cr2O7^2-/Cr^3+ redox couple and the electrode catalyst. The mediator undergoes reversible electron transfer with the chromium species in solution and then reversibly transfers electrons to/from the electrode, preventing direct irreversible interaction between Cr2O7^2- and the catalyst surface while maintaining high energy density benefits
Solution Approach 2:
The patent replaces the direct electrochemical reaction mechanism (where Cr2O7^2- directly interacts with the electrode catalyst) with an indirect mediated electron transfer mechanism. This substitution allows the system to achieve both high energy density from Cr2O7^2- and reversibility through the mediator's controlled electron transfer process
2Reliability
If traditional oxidants with 1 or 2 electron reductions are used, then rechargeability is maintained, but energy density and power density are limited
Solution Approach 1:
The patent changes the electron transfer parameter (n) of the oxidant from traditional 1 or 2 electrons to 6 electrons for Cr2O7^2-, while maintaining rechargeability through the mediator. This parameter change in the redox reaction stoichiometry directly increases the theoretical energy density without sacrificing reversibility
3Quantity of substance
If Cr2O7^2- concentration is increased to improve energy density, then power density increases, but irreversible side reactions increase
Solution Approach 1:
The soluble electron mediator serves as a protective intermediary that prevents direct contact between high concentrations of Cr2O7^2- and the electrode catalyst surface. The mediator handles electron transfer in a controlled manner, eliminating irreversible side reactions even at high oxidant concentrations, thereby enabling high power density operation
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 solution enables the use of Cr2O7^2- in redox flow batteries with significantly higher energy and power densities, achieving efficient regeneration and prolonged operation without undesirable side reactions, thus addressing the inefficiencies of previous Cr2O7^2- based systems.
Implementation Method 1
an electrochemically reversible electron mediator that is heterogeneously oxidized by the cathode to homogeneously oxidize Cr3+ back to Cr2O7^2-
Implementation Method 2
an ion-conducting membrane between the two half-cells
Implementation Method 3
one or more pumps to circulate stored catholyte and anolyte through the cathodic and anodic half cells
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
This invention describes a high-power, high-energy oxidant (catholyte) chemistry based on dichromate (CrVI as Cr2O7 2-) for use with a variety of fuels (anolytes) in redox flow batteries (RFBs, also known as reversible fuel cells), which reversibly store electricity as chemical energy. The reduction (discharge) of Cr2O7 2- to Cr3+ is natively irreversible at all investigated solid-state electrocatalysts, which has historically limited the employment of Cr2O7 2- to primary (non-rechargeable) cells, such as Grenet cells. The described invention overcomes this limitation by using a reversible redox couple, hereafter electron mediator, to heterogeneously donate electrons to the cathode electrocatalyst and homogeneously accept electrons from Cr3+ to regenerate Cr2O7 2-. RFBs employing this energy- and power-dense chemistry are suitable for low-cost energy storage applications, ranging from grid-level storage of renewable electricity to consumer electronics.