Figure shows ∆E 1→2 for two reaction steps, initial state (IS) to final state (FS), ∆E IS→FS and transition state (TS) to final state (FS), ∆E TS→FS . As we primarily study acidic reactions in this work, we perform DFT calculations in different cell sizes with varying the hydrogen atom concentration in the water layer in the IS. These hydrogen atoms spontaneously donate their electron to the electrode, changing the electrode potential, and become protons. The greater the number of protons per unit area, the lower the overall potential.