Redox Flow Cell for Long-Duration Energy Storage
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Solution Overview
Problem
Current stationary electrical energy storage systems face challenges in reducing lifecycle costs and extending storage duration beyond four to six hours to meet the demands of grid applications, particularly with high precious metal content and aggressive environments in proton exchange membrane electrolysis systems.
Innovation Solution
The system employs a redox flow cell with energy-bearing redox species dissolved in a liquid electrolyte solution, decoupling hydrogen and oxygen evolution reactions through separate unit operations, including a first redox flow cell with a H+/H2 half-cell and a second redox flow cell with a H2O/O2 half-cell, facilitated by a proton-permeable membrane, and an electrolyte regeneration process using a reactor or photoreduction cell to regenerate the redox species based on energy-market conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If proton exchange membrane electrolysis is used for hydrogen generation, then hydrogen production efficiency is improved, but system cost increases due to high precious metal content and thick membranes
Solution Approach 1:
The system is divided into two separate redox flow cells: one dedicated to hydrogen generation and another to oxygen generation. This segmentation allows each cell to be optimized for its specific function without requiring expensive precious metal catalysts and thick membranes in both cells, thereby reducing overall system cost while maintaining hydrogen production efficiency.
Solution Approach 2:
The oxygen evolution reaction is extracted from the hydrogen generation cell and placed in a separate cell. This extraction eliminates the need for expensive precious metal catalysts and thick membranes in the hydrogen generation cell, significantly reducing system cost while preserving hydrogen production capability.
2Duration of action of moving object
If energy storage duration is extended beyond four to six hours for grid applications, then energy delivery capability is improved, but system complexity and cost increase
Solution Approach 1:
The system enables continuous operation by regenerating the redox electrolyte in one cell while the other cell continues to generate hydrogen or oxygen. This continuous regeneration process allows the system to maintain energy storage and delivery capabilities for extended durations beyond four to six hours without requiring multiple complete system sets, thereby managing complexity while extending duration.
Solution Approach 2:
The redox electrolyte is circulated between the two cells, where it is consumed in one cell and regenerated in the other. This recovery and reuse of the electrolyte enables continuous operation for extended durations without requiring additional expensive materials, thus extending energy storage duration while controlling system complexity.
3Reliability
If thick membranes are used to ensure H2 and O2 separation, then separation reliability is improved, but system cost and complexity increase
Solution Approach 1:
The system uses two separate redox flow cells with physical separation between hydrogen generation and oxygen generation processes. This spatial segmentation eliminates the need for thick membranes within a single cell, achieving reliable H2 and O2 separation through system architecture rather than relying on thick membrane materials, thus reducing complexity and cost.
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 long-duration energy storage and delivery beyond current limitations, achieving efficient energy delivery for durations greater than six hours with lower operating costs and improved round-trip efficiency, utilizing low-cost energy-bearing redox pairs and reducing the need for high-cost materials.
Implementation Method 1
a proton permeable membrane separating the positive electrode and negative electrode sides
Implementation Method 2
The energy-bearing redox species can be associated with a reversible redox reaction having a standard electrode potential within the water electrolysis voltage window for the electrolyte solution
Implementation Method 3
a photoreduction cell having a photo-sensitive reducing agent, wherein the photoreduction cell is configured to receive solar radiation
Implementation Method 4
a reactor configured to react the liquid, energy-bearing, electrolyte solution comprising the energy-bearing redox species in a reduced state with an oxidizing agent to yield the energy-bearing redox species in an oxidized state
Implementation Method 5
a circulation sub-system configured to transfer a first, liquid, energy-bearing, electrolyte solution comprising the energy-bearing redox species in the oxidized state from the first redox flow cell to the photoreduction cell
Data Source
AI summary
Described herein are systems and methods of storing and delivering electrical using hydrogen at low-cost and for long-durations. The systems and methods use energy-bearing redox pairs that electrochemically bear energy through decoupled hydrogen and oxygen consumption and/or evolution reactions, which are typically associated with fuel cells. Each species of the energy-bearing redox pair is associated with a standard electrode potential within a water electrolysis voltage window for the electrolyte solution. Electrical energy delivery, hydrogen generation, electrolyte regeneration, or combinations thereof can be performed by logically or physically separated unit operations in a continuous manner, batch manner, or semi-batch manner facilitated by the energy-bearing redox pair.