The ET rate constant is measured at an equilibrium state where the Gibbs free energies of the products equal those of the reactants, i.e. E 0 IJ = 0. In addition, the electron energy in the solution (molecule's LUMO energy) must equilibrate with the Fermi-level in the electrode at the instance of ET. When an electrode-electrolyte combination is determined, E appl. is the only tool available to an operator to reach an equilibrium state. Suppose ∆A 0 IJ > 0, a negative value of E appl. is applied to the electrode to upshift the Fermi level. Hence, it minimizes the Gibbs free energy difference.