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Updated: Nov 24, 2025
09:49
A Protocol for Electrochemical Evaluations and State of Charge Diagnostics of a Symmetric Organic Redox Flow Battery
Published on: February 13, 2017
10.8K
A higher voltage Fe(ii) bipyridine complex for non-aqueous redox flow batteries
Claudina X Cammack1, Harry D Pratt1, Leo J Small1
1Sandia National Laboratories, Albuquerque, New Mexico 87185-00613, USA. tmander@sandia.gov.
Dalton Transactions (Cambridge, England : 2003)
|December 21, 2020
Summary
Non-aqueous redox flow batteries (RFBs) show promise for higher voltage and wider temperature ranges. This study optimized an existing RFB and explored new complexes to enhance stability and efficiency.
Area of Science:
- Electrochemistry
- Materials Science
- Energy Storage
Background:
- Non-aqueous redox flow batteries (RFBs) offer advantages over aqueous systems, including higher operating voltages and broader temperature tolerance.
- The Fe(bpy)3(BF4)2/Ni(bpy)3(BF4)2 system is an established asymmetric RFB with a 2.26 V potential.
Purpose of the Study:
- To optimize the performance of the Fe(bpy)3(BF4)2/Ni(bpy)3(BF4)2 asymmetric RFB, focusing on reducing capacity fade and improving energy efficiency.
- To synthesize and evaluate a series of substituted Fe(bpyR)3(BF4)2 complexes to achieve higher voltage RFBs by tuning redox potentials.
- To investigate the stability and efficiency of various symmetric and asymmetric RFBs utilizing these complexes.
Main Methods:
- Optimization of the existing 2.26 V Fe(bpy)3(BF4)2/Ni(bpy)3(BF4)2 asymmetric RFB over 20 cycles.
- Synthesis of substituted Fe(bpyR)3(BF4)2 complexes with varying R groups (e.g., -CF3, -CO2Me, -NH2).
- Electrochemical characterization of redox potentials for synthesized complexes, ranging from 0.94 V to 1.65 V vs. Ag/AgCl.
- Comparative analysis of symmetric and asymmetric RFBs to assess electroactive species stability and overall efficiency.
Main Results:
- The established Fe(bpy)3(BF4)2/Ni(bpy)3(BF4)2 RFB showed improved energy efficiency and reduced capacity fade over 20 cycles.
- A systematic tuning of redox potential was achieved for Fe(bpyR)3(BF4)2 complexes, with a potential window of 0.7 V observed.
- The unsubstituted Fe(bpy)3(BF4)2 demonstrated superior stability as a catholyte in both symmetric and asymmetric cells, achieving high voltage and coulombic efficiencies.
Conclusions:
- The unsubstituted Fe(bpy)3(BF4)2 is a highly stable and efficient catholyte for non-aqueous RFBs.
- Substituted Fe(bpyR)3(BF4)2 complexes offer a pathway to higher voltage non-aqueous RFBs through redox potential tuning.
- Further research into these complexes could lead to advanced energy storage solutions with improved performance characteristics.
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