Correlating microstructure and activity for polysulfide reduction and oxidation at WS2 electrocatalysts

Ifan E.L. Stephens, Caterina Ducati, Derek J. Fray

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Abstract

The polysulfide reduction and oxidation activity of WS2 electrocatalysts was studied. This was undertaken with a specific view to improve the efficiency of the polysulfide-bromine redox flow battery, for large scale energy storage. Using data from the literature, it is estimated that the catalysts would require exchange current densities of ̃0.7 to 1 mAcm-2 true microscopic surface area to enable them to become economically viable. The experiments were performed upon three different forms of WS2: platelet like particles of the 2H polytype of WS2 (2H-WS2), ball milled WS2 and inorganic fullerene-like WS2 (IF-WS2). The catalysts were characterized ex-situ using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis and N2 gas adsorption methods. Electrochemical measurements were performed at 35°C, in aqueous solutions of 1.8 M Na2S2.47 and 1 M NaOH, simulating the operating conditions of a half-charged polysulfide-bromine redox flow battery. The catalyst activity increased in the following order: IF-WS2 <2H-WS2. We attempt to rationalize this trend on the basis of the morphological features observed ex-situ. The exchange current density of the ball milled WS2, at ∼0.012 mA cm−2, falls short of the estimated target by a factor of ∼60 to 70.

Original languageEnglish
JournalJournal of The Electrochemical Society
Volume160
Issue number6
Pages (from-to)A757-A768
ISSN0013-4651
DOIs
Publication statusPublished - 2013

Bibliographical note

© 2013 The Electrochemical Society

Keywords

  • Bromine
  • Electrocatalysts
  • Gas adsorption
  • Scanning electron microscopy
  • Secondary batteries
  • Transmission electron microscopy
  • X ray diffraction
  • Polysulfides

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