http://pubs.acs.org/journal/aelccp
Redox-Enhanced Electrochemical Capacitors: Status, Opportunity, and Best Practices for Performance Evaluation Brian Evanko,† Shannon W. Boettcher,‡ Seung Joon Yoo,*,§,∥ and Galen D. Stucky*,†,§ †
Materials Department, University of California, Santa Barbara, California 93106, United States Department of Chemistry & Biochemistry, University of Oregon, Eugene, Oregon 97403, United States § Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States ∥ Materials Research Laboratory, University of California, Santa Barbara, California 93106, United States ‡
ABSTRACT: Redox-enhanced electrochemical capacitors (redox ECs) are a class of augmented electric double-layer capacitors utilizing reversible redox reactions of soluble redox couples in the electrolyte. These systems offer increased energy density, efficient power delivery, and simple construction. In this Perspective, we provide an overview of the emerging field of redox ECs, including the current status, advantages, and outstanding problems confronting their development. Our discussion is primarily focused on operating mechanisms and how they affect performance. We also provide a perspective on the advantage of dual-redox ECs and how to improve them based on fundamental design principles including self-discharge suppression strategies. Finally, we comment on best practices for device characterization, suggest performance-reporting protocols for redox ECs, and examine future directions for the field.
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electrodes accumulate oppositely charged ions at the interfaces between the electronic conductors (e.g., high-surface-area carbon) and the ionic conductor (the electrolyte) and create electric double-layers that store energy in the resulting electric fields. This charging mechanism based on electrostatic interaction enables EDLCs to fully charge or discharge in seconds with device-level specific power as high as 10 kW/kg.1 EDLCs also have calendar lifetimes on the order of decades and can cycle millions of times with minimal performance loss. These advantages compare favorably with secondary batteries, which typically have low specific power (
