Now we turn our attention to potentials in the RFB systems. There are three types of potentials in our study: (i) externally applied potential (E appl. ) that affects to the electrode's Fermi-level energy, (ii) solution phase onset potential (E 0 sol. ) that equals to free energy change of redox reaction divided by electron charge, and (iii) interfacial electrochemical reaction potential E 0 IJ = -∆A 0 IJ /e. These three components can be related by