1900

Origin of the catalytic activity at graphite electrodes in vanadium flow batteries

Abstract

For many electrochemical devices that use carbon-based materials such as electrolyzers, supercapacitors, and batteries, oxygen functional groups (OFGs) are considered essential to facilitate electron transfer. Researchers implement surface-active OFGs to improve the electrocatalytic properties of graphite felt electrodes in vanadium flow batteries. Herein, we show that graphitic defects and not OFGs are responsible for lowering the activation energy barrier and thus enhance the charge transfer properties. This is proven by a thermal deoxygenation procedure, in which specific OFGs are removed before electrochemical cycling. The electronic and microstructural changes associated with deoxygenation are studied by quasi in situ X-ray photoelectron and Raman spectroscopy. The removal of oxygen groups at basal and edge planes improves the activity by introducing new active edge sites and carbon vacancies. OFGs hinder the charge transfer at the graphite–electrolyte interface. This is further proven by modifying the sp2 plane of graphite felt electrodes with oxygen-containing pyrene derivatives. The electrochemical evolution of OFGs and graphitic defects are studied during polarization and long-term cycling conditions. The hypothesis of increased activity caused by OFGs was refuted and hydrogenated graphitic edge sites were identified as the true reason for this increase.

Funding source: Federal Ministry of Education and Research (BMBF) within the project Flow3DKat (03EK3053C) is acknowledged.
Related subjects: Production & Supply Chain
Countries: Germany
Loading

Article metrics loading...

/content/journal2220
2021-06-11
2021-10-21
http://instance.metastore.ingenta.com/content/journal2220
Loading

Supplements

Supplementary Material

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error