Free energy combines the chemical Gibbs free energy 𝐺 with the Fermi energy of the participating electrons in the electrode. This can be done by identifying three contributing terms: First, the electrochemical Gibbs free energy of the system at a reference state, here chosen to be the standard state, superscript ⊖. The second contribution stems from the electrostatic potential governed by the electrode potential 𝜑 𝑀 in the metal, subscript 𝑀. The third term stems from interactions of the system in the EDL due to its finite capacity with 𝜗 𝑖 being a sort of coverage value, called the effective coverage. The subscript 𝑖 being a placeholder for the systems identifier. This leads to Eqs. 2a and 2b with the subscript ∥ denoting a quantity at the reaction center.