Limited Accessibility to Surface Area Generated by Thermal Pretreatment of Electrodes Reduces Its Impact on Redox Flow Battery Performance

Thermal oxidation of carbon electrodes is a common approach to improving redox flow battery (RFB) performance, but the efficacy of this pretreatment method is unclear. Systematic studies reveal that much of the surface area generated by thermal oxidation manifests as nanometric pores inaccessible during electrochemical cell operation. In parallel, electrode-scale convection-reaction modeling reveals that increasing surface area improves performance to a point.

Scientific Achievement

A systematic study on thermally pretreated electrodes for redox flow batteries (RFBs) leveraging gas adsorption techniques, physicochemical spectroscopy, in situ flow cells, and a convection-reaction model suggests diminishing returns in RFB performance at longer pretreatment times due to hindered active species transport to recessed regions of the electrode.

Significance and Impact

Thermal pretreatment is a common approach to improve electrode properties for RFBs. This work demonstrates that much of the surface area generated by thermal oxidation may be underutilized, informing future electrode engineering and design efforts.

Research Details

  • Binder-free carbon paper electrodes (Freudenberg H23) were subjected to a range of pretreatment temperatures and times.
  • The physical surface area, measured by gas adsorption techniques, was compared to electrochemically-active surface area, estimated via double-layer capacitance.
  • Polarization in a single-electrolyte flow cell with a TEMPO redox couple showed little improvement with increasing surface area.
  • A simple convection-reaction model indicated that increasing surface area improves performance to a point, but mass transport to and the catalytic activity of the reaction sites offer greater comparative impact.

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DOI: 10.1021/acsaem.1c01980

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