Understanding the low corrosion potential and high corrosion resistance of nano-zinc electrodeposit based on electron work function and interfacial potential difference

Abstract

Nano-electrodeposition has been demonstrated to be more effective in protecting materials from corrosion, compared to conventional electrodeposition. However, debate still exists regarding why nanocrystalline electrodeposits show more negative corrosion potentials but lower corrosion rates than those of coarse-grained electrodeposits. In this work, we investigated corrosion behaviors of electrodeposited nanocrystalline and microcrystalline zinc coatings in a 3.5 wt% NaCl solution, and related them to the electron work functions of the coatings in order to understand the addressed issue based on the electron stability. It is demonstrated that the corrosion potential (ϕ_m) of a deposit depends on its electron work function (φ_m) and the contact potential difference at the electrodeposit/solution interface (Δ^m_sψ). φ_m reflects the stability of electrons in the deposit, while Δ^m_sψ reflects the environmental influence on the chemical stability of the deposit, which affects the actual corrosion rate. The present study shows that electrons in the nanocrystalline zinc coating are less confined due to its high-density grain boundaries, corresponding to lowered φ_m. However, Δ^m_sψ of the nanocrystalline coating is more positive than that of coarse-grained one, leading to a lower corrosion rate. This study helps end the debate and provide relevant information for optimize nanocrystalline electrodeposits.