Stability of highly supersaturated vanadium electrolyte solution and characterization of precipitated phases for vanadium redox flow battery

Abstract

The vanadium redox flow battery (VRFB) has been receiving great attention in recent years as one of the most viable energy storage technologies for large-scale applications. However, higher concentrations of vanadium species are required in the H 2 O-H 2 SO 4 electrolyte in order to improve the VRFB energy density. This might lead to unwanted precipitation of vanadium compounds, whose nature has not been accurately characterized yet. For this purpose, this study reports the preparation of V (II) ,V (III) ,V (IV) and V (V) supersaturated solutions in a 5 M H 2 SO 4 -H 2 O electrolyte by an electrolytic method, from the only vanadium sulfate compound commercially available (VOSO 4 ). The precipitates obtained by ageing of the stirred solutions are representative of the solids that may form in a VRFB operated with such supersaturated solutions. The solid phases are identified using thermogravimetric analysis, X-ray diffraction and SEM. We report that dissolved V (II) ,V (III) and V (IV) species precipitate as crystals of VSO 4 ,V 2 (SO 4 ) 3 and VOSO 4 hydrates and not in their anhydrous form; conversely V (V) precipitates as an amorphous V 2 O 5 oxide partially hydrated. The measured hydration degrees (respectively 1.5, 9, 3 and 0.26 mol of H 2 O per mol of compound) might significantly affect the overall engineering of VRFB operating with high vanadium concentrations.

A Ferricyanide Anion-Philic Interface Induced by Boron Species within Carbon Framework for Efficient Charge Storage in Supercapacitors

“…Therefore, the concentration of redox species in the electrolyte and the number of redox species that can be anchored by the carbon electrode together play a key role in capacitance. In fact, at the high concentration of redox ions, the electrostatic repulsion is enhanced, which prevents adsorption and the Faraday reaction from occurring on the electrode surface . Resultantly, the R-SCs are negatively impacted by an excess of K 3 Fe­(CN) 6 mediator in the electrolyte.…”

Long-Term Structural and Chemical Stability of Carbon Electrodes in Vanadium Redox Flow Battery

“…All three samples show two broad diffraction peaks at 26.5 and 44.0° representing (002) and (100) planes of graphitic structure, respectively. Interestingly, no diffraction lines were observed for dried electrolyte precipitates suggesting a highly disordered or amorphous nature and at variance with thermally induced crystalline precipitates from vanadium solutions. , The broad peak near 20° represents a disordered structure including a sp 3 bonding network in carbon electrodes . Electrochemical oxidation of graphitic layers into graphene oxide under aqueous acidic conditions has been widely reported .…”

Effect of Operating Conditions on the Capacity of Vanadium Redox Flow Batteries

“…[22][23][24][25] Due to the disparity in half-cell reaction rates and electrolyte concentrations, water may undergo electrolysis instead of vanadium during battery charging, leading to hydrogen oxidation and subsequent voltage loss. 26 In the event of inadequate tank sealing, oxidation of the anodic solution containing V 2+ may occur, leading to concentration imbalance and subsequent voltage loss. The migration of vanadium ions across the membrane inevitably leads to battery self-discharge and voltage decay.…”