Electrolyte potential (function) in battery modeling

Hi,

I just tried to model a flow battery in COMSOL and I wasn't sure what/how to enter the electrolyte potential in the initial value. I don't even know what's it referring to the electrode (tertiary current distribution for the electrodes). I looked up the model documentation for li ion battery and they have a function calculated by interpolation of E and t that I'm not sure where is it coming from. Let me know if anyone could give me some direction with that.

Thanks