Drastic Improvement in Capacity-Retention and Polarization of Vanadium Redox Flow Battery with Hydrophilic Co₃O₄ Nanostructure Modified Activated Graphite Felt Electrodes

Abstract

Metal oxides supported on carbon materials are reported as catalysts for the positive and negative electrodes of vanadium redox flow battery (VRFB). In this study, thermally activated graphite felt (TGF) is decorated with Co3O4 nanostructure by a low-temperature hydrothermal method. The functional groups on the TGF are believed to nucleate the Co3O4 particles establishing a covalent bridging between them. The bridge improves the electron tunnelling across the electrolyte/electrolyte interface, reducing the overpotential of vanadium redox reactions. The covalent bridge, coupled with the enhanced surface area of the nanostructured-Co3O4 coated TGF (TGF/Co-100–12), are responsible for improved VO2 +/VO2+ and V3+/V2+ redox kinetics in VRFB. A 25 cm2 VRFB employing TGF/Co-100–12 electrodes, compared to TGF, enhances the specific capacity from ∼ 38 Ah l−1 to ∼ 45 Ah l−1 and energy efficiency (EE) from 81 to 87.6% at 100 mA cm−2 and its capacity retention (after 50 cycles) is ∼ 100% higher than that of TGF based VRFB. Besides, a two-cell stack is demonstrated with an EE of 84% and 89% of initial capacity even after 50 cycles, and 3% loss in EE vis-à-vis single cell is mainly due to the additional contact resistance arising out of coupling the cells.

Hydrobromide Salt of Tribromodopamine as a Positive Electroactive Species with a Three-Electron Redox Process for Redox Flow Battery Applications

“…9−11 Hence, the unsubstituted aromatic sites of DA were substituted with -Br to obtain DABr 3 •HBr (Scheme 1). The 1 H and 13 C NMR spectra are given in Figures S1 and S2. This confirms that the synthesized product is a bromide salt, i.e., DABr 3 •HBr.…”

“…Physical Characterization. 1 H NMR and 13 C NMR of DABr 3 •HBr in DMSO-d 6 solvent were carried out with a 500 MHz Bruker NMR spectrometer. A silver nitrate test was carried out to test whether the product formed was a hydrobromide salt.…”

“…For comparison, another static battery was assembled (named the HBr-1,5-AQDS static battery) with 7 mL of 47 wt % hydrobromic acid (HBr) in water as the catholyte and 7 mL of 20 mM 1,5-AQDS as the anolyte, and GCD cycling was performed at a current density of 20 mA cm −2 for comparison purposes. The DABr 3 -V static battery was assembled using 7 mL of 10 mM DABr 3 •HBr in 3 M H 2 SO 4 as the catholyte and 7 mL of 30 mM V 3+ in 3 M H 2 SO 4 (prepared electrochemically 13 ) as the anolyte. A flow battery was also tested with 25 mL of 0.1 M DABr 3 •HBr as the catholyte and 300 mL of 0.06 M 1,5-AQDS as the anolyte at a current density of 10 mA cm −2 .…”

“…NMR and13 C NMR of DABr 3 •HBr prepared according to Scheme 1; post-cycling analysis including NMR, high-resolution mass spectra, digital images of the electrode and membrane, and UV−visible spectra; rate capability study of the DABr 3 •HBr-1,5-AQDS static battery; GCD curve of DABr 3 •HBr-V and HBr-1,5-AQDS static batteries; comparison of the capacity retention with other RFBs; DFT optimized structure (PDF) i l i a t e d…”

Binder-Free Flexible Three-Dimensional Porous Electrodes by Combining Microstructures and Catalysis to Enhance the Performance of Lithium-Oxygen Batteries

“…Graphite foam (GF), composed of interconnected graphite fibers, possesses many advantages such as a developed three-dimensional porous structure, high conductivity, good thermal stability, low cost, and easy recovery. − However, the electrochemical activity of GF is poor, and the improvement by acid or heat treatment cannot meet the requirements of lithium oxygen cells. , Combining electrode reaction, adsorption, and enrichment of oxygen, catalysis and microstructure should be considered comprehensively to enhance the performance of lithium-oxygen batteries, and it is necessary to improve the performance of GF by increasing more electrocatalysis activity.…”