The DFT calculations were carried out using the Vienna Ab-initio Simulation Package (VASP). The Fe(100) surface was modelled with a 3 × 3 × 1 supercell consisting of 8 atomic layers, containing a total of 72 iron atoms. The middle four atomic layers were fixed, while the two outermost layers were allowed to relax. To create a symmetric slab, a single explicit water layer was added to both the top and bottom surfaces, a method shown in previous studies to improve the convergence of the electrostatic potential in the bulk electrolyte region. The bulk electrolyte was modelled using the dielectric continuum solvation model with VASPsol, with the relative permittivity and Debye length set to 78.40 and 3.04 Å, respectively. The thickness of the implicit region was approximately 18 Å. All calculations were spin-polarized and performed using the projector augmented wave (PAW) method. The optPBE functional was used to treat the exchange-correlation (XC) energy, as this functional has demonstrated superior performance for modelling metal-water interactions. The kinetic energy cutoff was set to 500 eV, and all self-consistent structural optimizations converged at energy and force thresholds of 10 -5 eV and 0.03 eV/Å, respectively. To investigate changes in charge distribution upon surface modifications, the Bader charge analysis method was employed. The Cl-NEB method was used to transition state and reaction pathway calculations. The electrode potential was simulated by varying the total number of electrons (Δq) in the surface model from +2e to -2e in steps of 0.5e. The structures were fully optimized after each change in the number of electrons. The work function of a neutral surface was calculated as the difference between the Fermi energy and the vacuum potential. Work function can also be interpreted as the electron chemical potential at 0 K, while its negative value corresponds to the electrochemical potential. The electrode potential (U) was derived using the widely adopted double-reference method. The system was then referenced to the standard hydrogen electrode (SHE) using an empirical value of 4.6 V, as determined by the VASPsol model. Consequently, the applied potential can be calculated using Eq (1), where 𝐸𝐸 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 represents the Fermi level and 𝑈𝑈 𝑓𝑓𝑓𝑓𝑓𝑓 denotes the shift in the bulk electrolyte region to align it with zero.