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Institute of Physics

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10/09/2018

New paper published in Nature Communications on parameters determining charge storage mechanisms in nanoporous supercapacitors

To improve the performance of supercapacitors, a mechanistic understanding of ion electrosorption is required. In this work we identify parameters like salt concentration, charging velocity or cell design, controlling mechanisms of ion charge storage. Moreover, we show that charging initially leads to a non-equilibrium ion configuration even at extremely low cycling speed, followed by an increase of the total ion concentration, i.e. a charge-neutral equilibration.

Abstract:

A fundamental understanding of ion charge storage in nanoporous electrodes is essential to improve the performance of supercapacitors or devices for capacitive desalination. Here, we employ in situ X-ray transmission measurements on activated carbon supercapacitors to study ion concentration changes during electrochemical operation. Whereas counter-ion adsorption was found to dominate at small electrolyte salt concentrations and slow cycling speed, ion replacement prevails for high molar concentrations and/or fast cycling. Chronoamperometry measurements reveal two distinct time regimes of ion concentration changes. In the first regime the supercapacitor is charged, and counter- and co-ion concentration changes align with ion replacement and partially co-ion expulsion. In the second regime, the electrode charge remains constant, but the total ion concentration increases. We conclude that the initial fast charge neutralization in nanoporous supercapacitor electrodes leads to a non-equilibrium ion configuration. The subsequent, charge-neutral equilibration slowly increases the total ion concentration towards counter-ion adsorption.

 

Link to article (open access):  https://www.nature.com/articles/s41467-018-06612-4

 

 

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