First-principles study of coadsorption of Cu²⁺ and Cl^- ions on the Cu (110) surface

Motivated by the importance of Cl^- in the industrial electrolytic Cu plating process, we study the coadsorption of Cl^- and Cu²⁺ on the Cu (110) surface using first-principles density functional theory (DFT) calculations. We treat the solvent implicitly by solving the linearized Poisson-Boltzmann equation and evaluate the electrochemical potential and energetics of ions with the computational hydrogen electrode approach. We find that Cl^- alone is hardly adsorbed at sufficiently negative electrochemical potentials μ _Cl but stable phases with half and full Cl^- coverage was observed as μ _Cl is made more positive. For Cl^- and Cu²⁺ coadsorption, we identified five stable phases for electrode biases between -2V < U _SHE < 2V, with two being Cl^- adsorption phases, two being Cl^- + Cu²⁺ coadsorption phases and one being a pure Cu²⁺ adsorption phase. In general, the free energy of adsorption for the most stable phases at larger |U _SHE| are dominated by the energy required to move electrons between the system and the Fermi level of the electrode, while that at smaller |U _SHE| are largely dictated by the binding strength between Cl^- and Cu²⁺ adsorbates on the Cu (110) substrate. In addition, by studying the free energy of adsorption of Cu²⁺ onto pristine and Cl^- covered Cu (110), we conclude that the introduction of Cl^- ion does not improve the energetics of Cu²⁺ adsorption onto Cu (110).