High-power positive electrode based on synergistic effect of N- and WO3 -decorated carbon felt for vanadium redox flow batteries

Abstract

Although Vanadium Redox Flow Battery (VRFB) is well suitable for grid-scale application, their power-related cost must be reduced in order to boost the technology to the market, allowing their widespread commercialization. One effective way to make the VRFB a competitive and viable solution could be through the new strategies for improving the electrocatalytic activity of the electrodes with enhanced electrolyte/electrode interface characteristics. The greatly effective and enhanced-electron transfer could increase the current density with the decrement of the stack size. Herein, we report the synergistic effect demonstrated by N-and WO 3 -decorated carbon-based positive electrode, named HTNW electrode, which demonstrates the feasibility of achieving: i) enhanced electrocatalytic activity, indicating high rate towards VO 2+ /VO 2 + couple (promotion of oxygen and electron transfer processes), ii) decrement of the electron-transfer resistance from 75.62 Ω to 12.4 Ω for the pristine electrode and HTNW electrodes, respectively; iii) 51% of the electrolyte utilization ratio at high rates (i.e. 200 mA cm -2 ) with 70% of energy efficiency ; iv) increment of more than 50% of the power-peak in comparison with HT electrode.

Electrocatalysis at Electrodes for Vanadium Redox Flow Batteries

“…Improved energy efficiency, stable over 30 cycles, was reported. Carbon felt decorated with WO 3 and nitrogen has been proposed as a positive electrode [420]. In CVs decreased peak separation implied enhanced electrocatalytic activity and increased peak currents may also be due to increased EASA (not reported).…”

Mass Transfer and Reaction Kinetic Enhanced Electrode for High‐Performance Aqueous Flow Batteries

“…One effective way to enhance the electrocatalytic activity and thereby energy efficiency and power density is to deposit precious noble metals, such as Pt, Ru, Au, Bi, and Ir, but their high cost and higher hydrogen evolution rate hinder the large‐scale commercialization . Alternatively, low‐cost metal oxides such as ZrO 2 , Mn 3 O 4 , WO 3 , TiO 2 , CeO 2, PbO 2 ,, Ta 2 O 5 , Nd 2 O 3 , and Nb 2 O 5 have also been deposited on the GF to enhance the electrocatalytic activity. However, several critical parameters like their nanosize, nonuniform distribution, structural stability in the harsh vanadium redox flow battery (VRFB) environment, and stability against dissolution severely reduce the activity of the metal oxide catalysts.…”

Vanadium Oxygen Fuel Cell Utilising High Concentration Electrolyte

“…Vanadium trioxide (V 2 O 3 ) and vanadium pentoxide (V 2 O 5 ) powders were added to a sulphuric acid solution in equimolar quantities and heated subsequently to generate a required concentration of V(IV) solution by chemical dissolution. On addition of V 2 O 5 powder to a V 2 O 3 suspension, the V(III) ions chemically leach V 2 O 5 by shifting the equilibrium to form more soluble tetravalent V(IV) species [25]. The reaction can be represented as:…”

“…After pre-treatment, the NAFION ® 115 membrane was stored in DI water. To prevent the precipitation of vanadium species at higher concentration, precipitation inhibitors, ammonium sulphate (2 wt.%) and phosphoric acid (1 wt.%) were added to the 3.6 M Vanadium electrolyte solution based on previous work by Roe et al [25]. To prevent the V(V) formation during the electrolysis process, the volume used in the positive half-cell was twice that of one used in negative half-cell.…”

“…Thermal treatment in air at 400 • C and chemical treatment with H 2 SO 4 and HNO 3 developed by Skyllas-Kazacos group in the 1990s [16,17] remain the most effective, economical and easiest methods for activation of carbon-based materials. Surface modification of carbon-based electrodes with additives like WO 3 [18], W-doped Nb 2 O 5 [19], TiO 2 [20], CeO 2 [21] and ZrO 2 [22], Sb 3+ additive [23], Bismuth nanoparticles [24], N-and WO 3 - [25], graphene [26], TiN nanowires [27] have also been reported, resulting in improved battery performance.…”