Abstract
The underpotential deposition of Zn on polycrystalline Pt was studied in three different acid solutions for different Zn2+ concentrations. The voltammetric charges and the inhibition promoted by the maximum coverage of Zn ads in the hydrogen adsorption and evolution reactions were used to postulate adsorption models. It was shown that the co-adsorption of anions HSO4-, ClO4- and F-, either on the substrate or on the ad-atoms, exerts a marked influence in the ad-layer nature. On Pt, the maximum values found for the redissolution charge were around 210 muC cm-2, except for 10-3 mol L-1 Zn2+ in fluoride medium where a value of 350 muC cm-2 was obtained. A negligible inhibition of the hydrogen evolution reaction was recorded in sulfuric and perchloric acid solutions while a strong inhibition was found for fluoride medium. These results were related to the interaction of the large oxy-anions either with the substrate or the ad-atoms. Collection experiments were performed with the rotating ring-disk electrode system (RRDE) and the results confirmed the large charge value obtained in the HF electrolyte. The experiments performed with the RDDE also demonstrated that the voltammetric peaks analyzed here are associated with UPD Zn.
Highlights
The electrocrystallization of Ni-Zn alloys on different substrates is one of the most interesting subjects in applied electrochemistry
The underpotential deposition of metals has been extensively studied due to the possibility of promoting modifications on the catalyst surface in a specially controlled way. This phenomenon is associated to the interactions between ad-atoms and substrate that make it possible to deposit a metal M in a potential range more positive than the Nernst potential for the couple M/Mz+
Dorda et al.[4] have analyzed the deposition of Zn on Pt from alkaline solutions by cyclic voltammetry, proposing a poisoning of the surface by zinc ad-atoms, which was revealed by the inhibition of the hydrogen adsorption peaks
Summary
The electrocrystallization of Ni-Zn alloys on different substrates is one of the most interesting subjects in applied electrochemistry. Dorda et al.[4] have analyzed the deposition of Zn on Pt from alkaline solutions by cyclic voltammetry, proposing a poisoning of the surface by zinc ad-atoms, which was revealed by the inhibition of the hydrogen adsorption peaks.
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