where C + represents a monovalent cation, and n is the number of cations interacting with the sulfonate group. The breaking of the -[𝑆𝑂 - . ] 678 ⋯ 𝑛𝐶 5 interaction carries an energetic cost, and the stronger the electrostatic interation is, the higher the energetic cost will be. As the pH of the liquid electrolyte decreases from 3 to 1, the concentration of the cation species, i.e., protons, increases by two orders of magnitude.