The vanadium crossover is controlled by diffusion, migration, and convection across the membrane. It was reported that the following side reactions occur when vanadium ions move to the counter electrode side (1):
It is also known that the water transfer through the membrane is controlled by three mechanisms as follows (2):
1) Water molecules are transferred along with a vanadium ion that moves to the counter electrode
2) Water molecules are transferred along with a proton to satisfy electro-neutrality
3) Water molecules are transferred by osmosis phenomenon due to vanadium concentration difference between two electrolytes
The above vanadium and water transfer through membrane strongly denpends on the physico-chemical properties of the membrane. In this study, we aim to elucidate crossover phenomenon and its consequence in a VRFB by taking computational apporach with a physics-based multi-dimensional VRFB model that has capability of simulating complex species transfer mechanisms. Further, we analyze the cause and effect of each crossover mechanism according to the different types of membranes such as anion exchange membrane, cation exchange membrane, and micro-porous separator. We conclude our study by suggesting electrolyte rebalancing strategies for each type of membrane.
 K. W. Knehr, Ertan Agar, C. R. Dennison, A. R. Kalidindi, and E. C. Kumbur, J. Electrochemical Society 159(2012) A1446-A1459