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An Aqueous Redox Flow Battery Using CO2 as an Active Material with a Homogeneous Ir Catalyst.

Ryoichi Kanega1, Erika Ishida1, Takaaki Sakai2

  • 1Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8565, Japan.

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Summary
This summary is machine-generated.

This study presents a novel aqueous redox flow battery using iridium catalysts for direct electricity storage via the carbon dioxide (CO2) and formate redox pair, bypassing energy-intensive hydrogen conversion.

Keywords:
CO2FormateIridiumRedox Flow BatteryXAFS

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Area of Science:

  • Electrochemistry
  • Energy Storage
  • Catalysis

Background:

  • Traditional hydrogen-based energy storage systems involving carbon dioxide (CO2) conversion suffer from significant energy losses (≈70% during H2 generation, ≈40% during electricity recovery).
  • Developing efficient methods for direct CO2 utilization in energy storage is crucial for improving overall system efficiency.

Purpose of the Study:

  • To design and evaluate an aqueous redox flow battery system that directly utilizes the CO2-formate redox couple for electricity storage and generation.
  • To overcome the inherent inefficiencies associated with hydrogen-based energy storage pathways.

Main Methods:

  • Development of an aqueous redox flow battery employing homogeneous iridium (Ir) catalysts.
  • Utilizing the CO2-formate redox pair as the active electrochemical species.
  • In situ fluorescence X-ray absorption fine structure (XAFS) spectroscopy for real-time analysis of catalytic species.

Main Results:

  • The developed system achieved a maximum discharge capacity of 10.5 mAh (1.5 Ah L-1).
  • Demonstrated excellent cycling stability with a low capacity decay rate of 0.2% per cycle over 50 cycles.
  • Attained a total turnover number of 2550, indicating robust catalytic performance.
  • In situ XAFS confirmed the active iridium species exists in a high valence state (IrIV) during operation.

Conclusions:

  • The CO2-formate redox flow battery offers a promising alternative for direct electricity storage, mitigating energy losses associated with hydrogen intermediates.
  • Homogeneous iridium catalysts exhibit high activity and stability in this aqueous redox flow system.
  • The IrIV species is identified as the key active component, providing insights for further catalyst optimization.