Graphene‐Nanowall‐Decorated Carbon Felt with Excellent Electrochemical Activity Toward VO₂⁺/VO²⁺ Couple for All Vanadium Redox Flow Battery

Abstract

3D graphene‐nanowall‐decorated carbon felts (CF) are synthesized via an in situ microwave plasma enhanced chemical vapor deposition method and used as positive electrode for vanadium redox flow battery (VRFB). The carbon fibers in CF are successfully wrapped by vertically grown graphene nanowalls, which not only increase the electrode specific area, but also expose a high density of sharp graphene edges with good catalytic activities to the vanadium ions. As a result, the VRFB with this novel electrode shows three times higher reaction rate toward VO2 +/VO2+ redox couple and 11% increased energy efficiency over VRFB with an unmodified CF electrode. Moreover, this designed architecture shows excellent stability in the battery operation. After 100 charging–discharging cycles, the electrode not only shows no observable morphology change, it can also be reused in another battery and practical with the same performance. It is believed that this novel structure including the synthesis procedure will provide a new developing direction for the VRFB electrode.

Titanium as a Substrate for Three‐Dimensional Hybrid Electrodes for Vanadium Redox Flow Battery Applications

“…Moreover, in the case of NCNTs@Ti foil, the values of ΔE p are 0.16, 0.13 and 0.19 V vs MSE when t 1 was set to 60, 90, and 120 s, respectively, while in the case of NCNTs@Ti mesh, the values of ΔE p are 0.28, 0.20, and 0.33 V vs MSE, demonstrating that the prepared electrodes provide good redox activity. These promising results are not only superior to those obtained with graphene-nanowallmodified carbon felt (lowest ΔE p = 0.339 V), [8] but also they are close to the best previously published results obtained on a carbon nanofiber/nanotube (CNF/CNT) composite catalysts grown on carbon felt (CNF/CNT-700, lowest ΔE p = 136.12 mV) as active electrode material in a VRFB. [25] A slight influence of the iron deposition time is observed with 90 s in both cases as shown in Figures 6 (a) and (b), providing the highest current densities and the lowest peak potential differences.…”

“…However, it was also shown that this standard electrode material (carbon felt/carbon nonwoven) has to be activated in order to provide an acceptable catalytic activity for vanadium ion redox conversion, and even in this case further improvement is desired to overcome kinetic limitations, as detailed above. Thus, recent research focusses on the investigation of catalytically active carbon material, such as carbon fibres, carbon nanotubes, mesoporous carbon, carbon nanospheres, and more.…”

Vertically Aligned Graphene Nanosheet Arrays: Synthesis, Properties and Applications in Electrochemical Energy Conversion and Storage

“…[132] To fabricate practicable and recyclable electrodes with reduced cost, VAGNAs were prepared on carbon felt by PECVD (Figure 10b-d). [133] Compared with the original carbon felt, the VAGNAs-decorated carbon-felt exhibited much decreased charge transfer resistance. A three times higher reaction rate toward VO 2 + /VO 2+ redox couple, and an increase of energy efficiency by 11% over VRFB were achieved (Figure 10e,f).…”

Performance of Different Carbon Electrode Materials: Insights into Stability and Degradation under Real Vanadium Redox Flow Battery Operating Conditions

“…4 To enhance electrochemical activity and wettability of carbon based materials in VRBs, different surface modification methods have been used. Carbon electrodes have been coated with metals such as iridium, 5 doped with nitrogen 6 or decorated with nanomaterials such as graphene-nanowalls 7 or graphite carbon nanotubes. 8 Recently, Zhou et al reported activation of carbon papers and carbon cloth by heat-treatment and subsequent etching with KOH.…”