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Media type:
E-Article
Title:
Kinetics of VIII and VII Sulfate Precipitation Processes in Negative Half‐Cell Electrolyte of the Vanadium Redox Flow Battery
Contributor:
Mousa, Asem;
Skyllas‐Kazacos, Maria
Published:
Wiley, 2017
Published in:
ChemElectroChem, 4 (2017) 1, Seite 130-142
Language:
English
DOI:
10.1002/celc.201600426
ISSN:
2196-0216
Origination:
Footnote:
Description:
AbstractThe low‐temperature stability and precipitation behaviour of VIII and VII sulfate solutions are critical for the optimal operation of vanadium redox flow batteries. In this study, the kinetics of the VIII and VII sulfate precipitation processes have been studied at different temperatures and sulfate concentrations. Kinetic studies of the precipitation of stagnant vanadium(III) sulfate solutions followed a first‐order rate law with rate constants on the order of 0.007 h−1 and an activation energy of about 14.6 kJ mol−1. Stirring the solutions at low supersaturation causes a ten‐fold increase in the rate of precipitation and also resulted in a change in the precipitation mechanism from diffusion controlled to a surface reaction controlled mechanism with an activation energy of 37.0 kJ mol−1. Stagnant solutions at high supersaturation followed a second‐order rate law with an activation energy of 27.0 kJ mol−1 for the first 30 % of the precipitation process. The process becomes first order in the last 70 % with an activation energy of 14.3 kJ mol−1, indicating a change in the reaction mechanism to a diffusion‐controlled mechanism. Kinetic studies of the precipitation of vanadium(II) sulfate solutions showed that both stagnant and stirred solutions follow a first‐order rate law with a low activation energy (10.7 and 14.5 kJ mol−1, respectively). This indicates a diffusion‐controlled precipitation mechanism under both conditions.