Abstract
Safe and inexpensive energy storage devices with long cycle lifetimes and high power and energy densities are mandatory for the development of electrical power grids that connect with renewable energy sources. In this study, we demonstrated metal-free aqueous redox capacitors using couples comprising low-molecular-weight organic compounds. In addition to the electric double layer formation, proton insertion/extraction reactions between a couple consisting of inexpensive quinones/hydroquinones contributed to the energy storage. This energy storage mechanism, in which protons are shuttled back and forth between two electrodes upon charge and discharge, can be regarded as a proton rocking-chair system. The fabricated capacitor showed a large capacity (>20 Wh/kg), even in the applied potential range between 0–1 V, and high power capability (>5 A/g). The support of the organic compounds in nanoporous carbon facilitated the efficient use of the organic compounds with a lifetime of thousands of cycles.
Highlights
Safe and inexpensive energy storage devices with long cycle lifetimes and high power and energy densities are mandatory for the development of electrical power grids that connect with renewable energy sources
Support of the organic compounds in the nanoporous carbon should play a crucial role for the effective use of the capacity of organic compounds
As indicated above, the organic compounds held in nanoporous carbon contributed to the energy storage
Summary
Metal-free aqueous redox capacitor via proton rocking-chair system in an organic-based couple. In addition to the electric double layer formation, proton insertion/extraction reactions between a couple consisting of inexpensive quinones/hydroquinones contributed to the energy storage This energy storage mechanism, in which protons are shuttled back and forth between two electrodes upon charge and discharge, can be regarded as a proton rocking-chair system. Reports have shown that both the capacitance and energy density were enhanced by the redox reactions of quinones loaded in activated carbon via impregnation[17,20], grafting[18,19], or dissolution in the electrolyte[22,23] Most such redox capacitors consisted of at least one unmodified or unloaded carbon electrode, and redox capacitors configured from two different electrodes employing a couple based on two organic compounds having different reaction potentials have rarely been investigated, despite their promise for further increases in energy density. The manufactured capacitor exhibited promising performance in terms of high energy density, high power density, and long cycle lifetime
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