Scanning electrochemical microscopy and hydrodynamic voltammetry investigation of charge transfer mechanisms on redox active polymers

Mark Burgess, Kenneth Hernández-Burgos, Burton H. Simpson, Timothy Lichtenstein, Sona Avetian, Gavvalapalli Nagarjuna, Kevin J. Cheng, Jeffrey S. Moore, Joaquín Rodríguez-López

Research output: Contribution to journalArticle

Abstract

We recently showed that viologen-based redox active polymers (RAPs) with molecular weights between 21 and 318 kDa are attractive charge storage materials as anolytes for size-selective non-aqueous redox flow batteries. Here, we characterize the electron transfer mechanisms of these RAPs, as well as a ferrocene based catholyte RAP, in acetonitrile/Li+ electrolyte. We utilized scanning electrochemical microscopy (SECM) and rotating disk electrode (RDE) voltammetry to measure the rate of electron transfer and the rate of charge hopping between neighboring pendants along the insulating backbone of RAPs. The electron transfer kinetics of a 271 kDa ferrocene RAP mimic the facile kinetics of its monomer repeating unit. In contrast, viologen RAPs displayed RDE and SECM signatures that suggest a preceding chemical step to electron transfer. Viologen RAPs adsorb strongly to the electrode surface and create a redox active film that controls the rate of electron transfer via self-exchange. In addition, finite element simulations including a preceding chemical step demonstrated that a purely mass-transfer limited model is insufficient to recreate the viologen RAP feedback SECM response. The mechanistic insight obtained by combining SECM and RDE provided a powerful toolset for understanding and enhancing RAP reactivity for size-selective flow battery applications.

Original languageEnglish (US)
Pages (from-to)H3006-H3013
JournalJournal of the Electrochemical Society
Volume163
Issue number4
DOIs
StatePublished - Jan 1 2016

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Surfaces, Coatings and Films
  • Electrochemistry
  • Materials Chemistry

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