Sho-ichiro Sakai

Self-Organized Periodic Growth of Stacked Hexagonal Wafers in Synchronization with a Potential Oscillation in Zinc Electrodeposition

Electrodeposition of zinc (Zn) from a strongly alkaline Zn(II) solution showed a potential oscillation in the region of the current density exceeding the diffusion-limited one, accompanied by the formation of dendrites with a stacked wafer structure. Scanning electron microscopic inspection showed that the dendrites changed their shape periodically in synchronization with the potential oscillation from thick hexagonal wafers on the negative potential side to thin maple-leaf-like wafers on the positive potential side and inversely. In situ electrochemical quartz crystal microbalance measurements revealed that the rate of Zn deposition also oscillated in synchronization with the oscillation. A mechanism is proposed to explain the oscillation and the dendrite formation by taking into account coupling of autocatalytic Zn-crystal growth, in close relation with Mullins-Sekerka instability, and autocatalytic surface oxidation at the close packed crystal faces leading to surface passivation.

Promoted Dissociative Adsorption of Hydrogen Peroxide and Persulfate Ions and Electrochemical Oscillations Caused by a Catalytic Effect of Adsorbed Bromine

Adsorbed bromine on Pt and Au electrodes acts as a catalyst for dissociative adsorption of H 2 O 2 and S 2 O 2- 8 , similar to adsorbed OH (and adsorbed iodine). This fact is revealed by analyses of newly found negative differential resistances and electrochemical oscillations, appearing in a potential region where the surface coverage of adsorbed bromine (θ Br ) decreases steeply. The present result further supports the generality of a catalytic effect of adsorbed electronegative species such as OH, Br, and I on the dissociative adsorption of peroxides such as H 2 O 2 and S 2 O 2- 8 .