Details

Autor(en) / Beteiligte

• Radinger, Hannes
• Ghamlouche, Ahmad
• Ehrenberg, Helmut
• Scheiba, Frieder

Titel

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

Ist Teil von

• Journal of materials chemistry. A, Materials for energy and sustainability, 2021-09, Vol.9 (34), p.1828-18293

Ort / Verlag

Cambridge: Royal Society of Chemistry

Erscheinungsjahr

2021

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• 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 sp 2 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. Deoxygenated graphite electrodes exhibited an overall higher electrocatalytic activity than the oxygen-rich starting material. Free edge sites were therefore identified as the origin of the charge transfer process for the vanadium redox reactions.