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

Abstract

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).