Journal
ELECTROCHIMICA ACTA
Volume 140, Issue -, Pages 116-124Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.electacta.2014.03.104
Keywords
Supercapacitors; Activation control; Diffusion control; Carbon; Ruthenium Oxide
Categories
Funding
- Natural Sciences and Engineering Research Council (NSERC)
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The self-discharge profiles of manganese oxide films were examined to identify the self-discharge processes for these pseudocapacitive films. The profile shape was compared to four self-discharge models: an activation-controlled Faradaic reaction only; resistance-limited charge redistribution only; diffusion-limited charge redistribution only; or an activation-controlled Faradaic reaction coupled with charge redistribution. Hardware circuitry models (e.g. a transmission line) were used to model the activation-controlled reaction and resistance-limited charge redistribution. Ruthenium oxide was used as an experimental model for diffusion-limited charge redistribution, while highly porous carbon undergoing surface oxidation modelled the activation-controlled Faradaic reaction coupled with charge redistribution. Comparison of the manganese oxide self-discharge to these models showed an, as yet unidentified, activation-controlled Faradaic reaction on the manganese oxide surface, with a Tafel slope of 67 +/- 5 mV. Additionally, the presence of charge redistribution was indicated in these films for the first time. During self-discharge, the activation-controlled reaction discharges the manganese oxide surface, setting up a potential differential between the surface and the bulk - where the surface has a lower potential. The result of this potential differential is that during charge redistribution the bulk manganese oxide provides charge to the surface, effectively slowing self-discharge. (C) 2014 Elsevier Ltd. All rights reserved.
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