Tunable Oxygen Functional Groups as Electrocatalysts on Graphite Felt Surfaces for All‐Vanadium Flow Batteries

Abstract

A dual oxidative approach using O2 plasma followed by treatment with H2 O2 to impart oxygen functional groups onto the surface of a graphite felt electrode. When used as electrodes for an all-vanadium redox flow battery (VRB) system, the energy efficiency of the cell is enhanced by 8.2 % at a current density of 150 mA cm(-2) compared with one oxidized by thermal treatment in air. More importantly, by varying the oxidative techniques, the amount and type of oxygen groups was tailored and their effects were elucidated. It was found that O-C=O groups improve the cells performance whereas the C-O and C=O groups degrade it. The reason for the increased performance was found to be a reduction in the cell overpotential after functionalization of the graphite felt electrode. This work reveals a route for functionalizing carbon electrodes to improve the performance of VRB cells. This approach can lower the cost of VRB cells and pave the way for more commercially viable stationary energy storage systems that can be used for intermittent renewable energy storage.

Electrocatalysis at Electrodes for Vanadium Redox Flow Batteries

“…PAN-based felt was best for both electrodes after heat-and plasma-treatment. Treatment of graphite felt in oxygen plasma followed by treatment with H 2 O 2 left numerous oxygen functional surface groups [342]. Beneficial effects were found at both electrodes of a VRFB; cell energy efficiency at j = 150 mA·cm −2 is improved by 8.2% without obvious decay for 55 cycles.…”

On the Resistances of a Slurry Electrode Vanadium Redox Flow Battery

“…VRBs use vanadium as redox‐active species, where redox reactions of VO 2+ −VO 2 + as catholyte and V 3+ −V 2+ as anolyte happen simultaneously. Solid porous electrodes, such as carbon felts or papers, are widely used in these batteries . The electrodes do not contribute to the redox reactions, except for the fact that they provide sufficient surface area for electrolyte reactions, leading to higher current densities.…”

Glucose-derived hydrothermal carbons as energy storage booster for vanadium redox flow batteries

“…Moreover, VRFBs is operational flexible, because the energy capacity and power generation can be adjusted independently of one another [13][14][15] . However, the energy efficiency of VRFBs is determined by the electrochemical activity of the porous electrode, which is preferable to have a high electroactive surfaces and conductivity for the redox reactions [16][17][18] . In view of these issues, a highly efficient and low-cost electrode is highly desirable for VRFBs.…”