What Structural Features Make Porous Carbons Work for Redox-Enhanced Electrochemical Capacitors? A Fundamental Investigation
Date
2021-02Author
Zhao, Yang
Taylor, Erin E.
Hu, Xudong
Evanko, Brian
Zeng, Xiaojun
Wang, Hengbin
Ohnishi, Ryohji
Tsukazaki, Takaki
Li, Jian-Feng
Stadie, Nicholas P.
Yoo, Seung Joon
Stucky, Galen D.
Boettcher, Shannon W.
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Show full item recordAbstract
The addition of redox-active molecules into electrochemical-capacitor electrolytes provides increased specific energy density. Here we illustrate the underlying operational mechanisms and design principles for carbons with hierarchical pore sizes in the micropore (0.6–2 nm) to mesopore (2–3 nm, 5–30 nm) range as electrode materials in redox-enhanced electrochemical capacitors. When using iodide as a model redox additive, we discover that the redox capacity is correlated to the pore volume of the carbon electrodes when void space is included. The fastest rates are typically observed with pore-sizes >1 nm, while slow self-discharge requires pores <1 nm. When used without an ion-selective-membrane separator, the delivered capacity correlated with the quantity of redox species held within the carbon. A commercial microporous carbon, MSC30, with substantial hierarchy in pore size, including small <0.8 nm pores and larger 1.1–3 nm pores, showed the best overall performance, illustrating key design principles.
Citation
Zhao, Y., Taylor, E.E., Hu, X., Evanko, B., Zeng, X., Wang, H., Ohnishi, R., Tsukazaki, T., Li, J.F., Stadie, N.P. and Yoo, S.J., 2021. What Structural Features Make Porous Carbons Work for Redox-Enhanced Electrochemical Capacitors? A Fundamental Investigation. ACS Energy Letters, 6(3), pp.854-861.