Underpotential Deposition Of Zn Research Articles

Reversible Zn Metal Anodes Enabled by Trace Amounts of Underpotential Deposition Initiators

AbstractRoutine electrolyte additives are not effective enough for uniform zinc (Zn) deposition, because they are hard to proactively guide atomic‐level Zn deposition. Here, based on underpotential deposition (UPD), we propose an “escort effect” of electrolyte additives for uniform Zn deposition at the atomic level. With nickel ion (Ni2+) additives, we found that metallic Ni deposits preferentially and triggers the UPD of Zn on Ni. This facilitates firm nucleation and uniform growth of Zn while suppressing side reactions. Besides, Ni dissolves back into the electrolyte after Zn stripping with no influence on interfacial charge transfer resistance. Consequently, the optimized cell operates for over 900 h at 1 mA cm−2 (more than 4 times longer than the blank one). Moreover, the universality of “escort effect” is identified by using Cr3+ and Co2+ additives. This work would inspire a wide range of atomic‐level principles by controlling interfacial electrochemistry for various metal batteries.

Reversible Zn Metal Anodes Enabled by Trace Amounts of Underpotential Deposition Initiators.

Routine electrolyte additives are not effective enough for uniform zinc (Zn) deposition, because they are hard to proactively guide atomic-level Zn deposition. Here, based on underpotential deposition (UPD), we propose an "escort effect" of electrolyte additives for uniform Zn deposition at the atomic level. With nickel ion (Ni2+ ) additives, we found that metallic Ni deposits preferentially and triggers the UPD of Zn on Ni. This facilitates firm nucleation and uniform growth of Zn while suppressing side reactions. Besides, Ni dissolves back into the electrolyte after Zn stripping with no influence on interfacial charge transfer resistance. Consequently, the optimized cell operates for over 900 h at 1 mA cm-2 (more than 4 times longer than the blank one). Moreover, the universality of "escort effect" is identified by using Cr3+ and Co2+ additives. This work would inspire a wide range of atomic-level principles by controlling interfacial electrochemistry for various metal batteries.

Cathodic Zn underpotential deposition: an evitable degradation mechanism in aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are promising for large-scale energy storage, but their development is plagued by inadequate cycle life. Here, for the first time, we reveal an unusual phenomenon of cathodic underpotential deposition (UPD) of Zn, which is highly irreversible and considered the origin of the inferior cycling stability of AZIBs. Combining experimental and theoretical simulation approaches, we propose that the UPD process agrees with a two-dimensional nucleation and growth model, following a thermodynamically feasible mechanism. Furthermore, the universality of Zn UPD is identified in systems, including VO2//Zn, TiO2//Zn, and SnO2//Zn. In practice, we propose and successfully implement removing cathodic Zn UPD and substantially mitigate the degradation of the battery by controlling the end-of-discharge voltage. This work provides new insights into AZIBs degradation and brings the cathodic UPD behavior of rechargeable batteries into the limelight.

(Invited) Electrochemical Tuning Sensing and Catalytic Performance of Catalytic Materials -from Nanoscale to Atomic Scale

In this talk, we will introduce two facile methods for the preparation of a nanoporous Ag foam and a promising electrocatalyst for the oxygen reduction reaction (ORR). Ag has a high electrical and thermal conductivity, low cost, and is relatively abundant in the earth compared to other Pt-group metals. Unlike Pt-related noble metals, the poor hydrogen evolution reaction (HER) activity of Ag in acidic environments makes it rarely considered as a potential HER electrocatalyst. We demonstrate a spongy-like highly nanoporous Ag foam obtained using a simple Ag surface treatment through the repetitively electrochemical anodic formation of AgBr/cathodic reduction back to Ag exhibited Pt-like high HER activities. Bimetallic Pt-Ni with Pt on the outermost layer and an innermost layer enriched in Ni, referred to as (Pt3Ni(Pt-skin), is a promising configuration of electrocatalyst for the ORR in fuel cells. We prepare a core (Pd)/shell (Pt3Ni(Pt-skin)) catalyst (Pt3Ni(Pt-skin)/Pd/C) from Zn underpotential deposition (UPD) on a Ni UPD modified Pd/C catalyst, facilitating Pt atomic layer-by-layer growth on the Ni surface through the galvanic replacement process. The Pt3Ni(Pt-skin) thin layer with ultra-low Pt loading presents not only a breakthrough in Pt specific activity and Pt mass activity, both of which were superior to state-of-the-art Pt-Ni catalysts, but also in high durability owing to the perfect Pt3Ni(Pt-skin) construction

Electrochemical Atomic Layer Deposition of Copper Mediated By Underpotentially Deposited Zinc

Electrochemical Atomic Layer Deposition (e-ALD) is attractive for materials fabrication in a variety of applications including nano-electronics, catalysis and energy conversion. This technique enables deposition of ultrathin metal and metal alloy films, while providing unprecedented atomic-level control over surface topography through layer-by-layer assembly of metal monolayers [1, 2]. Conventional e-ALD of copper (Cu) consists of two key steps repeated sequentially [3]: (i) Underpotential deposition (UPD) of a sacrificial metal monolayer such as lead (Pb) followed by (ii) Surface-Limited Redox Replacement (SLRR) of the sacrificial Pb-UPD layer by nobler Cu. In this study, we present a novel lead-free process for e-ALD of Cu mediated by zinc (Zn) UPD. This process eliminates lead-containing chemistries and thus it is advantageous in terms of its practical applicability. In this process, a sacrificial monolayer of Zn is underpotentially deposited onto the substrate (e.g., ruthenium Ru). Under open-circuit conditions, the sacrificial Zn monolayer undergoes redox replacement by nobler Cu. This provides a monolayer of Cu on the substrate surface. UPD-SLRR cycles are repeated to build multi-layers of Cu with controlled thickness while minimizing surface roughness evolution. These are characteristics of true e-ALD. Cyclic voltammetry (CV) was performed to confirm the Zn-UPD behavior on a PVD Cu substrate from an alkaline electrolyte containing complexed Zn2+. Quartz crystal microgravimetry (QCM) was employed to further study the Zn-UPD process on a Cu coated quartz crystal. The frequency of the quartz crystal decreased (indicative of mass addition) and reached a time-invariant value of -7 Hz after complete formation of a Zn-UPD monolayer. Based on results of CV and microgravimetry, the following Cu e-ALD protocol was established: Underpotential deposition of Zn onto the Cu substrate at -1.1 V vs. Ag/AgCl for 20 sec followed by SLRR of Zn-UPD monolayer by Cu under open-circuit conditions. In the present talk, we will demonstrate the basic feasibility of the proposed novel Cu e-ALD process. Fig. 1 shows the potential and QCM frequency response during the Cu e-ALD process. The important features of the process are as follows: (i) The steady-state QCM frequency shift of ~7 Hz during the Zn-UPD step, indicative of a mass gain of about 124 ng/cm2 (i.e., ~1 monolayer of Zn). (ii) During the SLRR period, the potential drifts anodic indicating replacement of the Zn monolayer by nobler Cu. (iii) The frequency shift is constant during the SLRR period. (iv) After each SLRR cycle, consistent frequency decrease of ~ 6–7 Hz is observed during the Zn-UPD step, indicating the layer-by-layer growth of smooth Cu layers. In this talk, we will discuss the Cu e-ALD deposit characteristics such as the thickness, roughness and composition. Possible extensions of the proposed e-ALD approach to fabrication of other metallic nano-films will be discussed.

Underpotential shift in electrodeposition of metal adlayer on tellurium and the free energy of metal telluride formation

Underpotential deposition (UPD) of metals on polycrystalline tellurium film shows much similarity with UPD of metals on foreign metals, but the underpotential shifts on tellurium show no correlation with differences of work functions of the substrate and the deposited metal. In this work, we have evaluated the underpotential shifts of Pb, Cd, Zn, Bi, In, Sn, and Cu UPD on tellurium from cyclic voltammograms and potentiodynamic profiles of inverse charge transfer resistance derived from potentiodynamic impedance spectra, and shown a correlation of the underpotential shifts with the free energy of the corresponding metal telluride formation. The correlation can help to predict underpotential shifts for metals with complications in the measurement of this parameter.

Formation of zinc–oxianion complex adlayer by underpotential deposition of Zn on Au(1 1 1) electrode: Preferential formation of zinc monohydrogen phosphate complex in weakly acidic solutions

The underpotential deposition (upd) of zinc was studied on Au(111) electrode in weakly acidic solutions by voltammetry. The difference of anion co-adsorption strength was investigated on upd Zn in the solutions containing phosphate, sulfate, perchlorate, and halides. The order of anion co-adsorption strength was found to be phosphate>sulfate, phosphate≫perchlorate, and phosphate≫halides. We present the electrochemical evidence that no co-adsorption of halide progresses on upd Zn at E>−0.7V (vs. SCE) in spite of the relatively high adsorbability of halide on Au(111). In 0.1M KH2PO4 (pH=4.4), the amount of charge density of the upd Zn stripping corresponded to that of 1/3 monolayer of the Zn adlayer formed as a result of mono-electron transfer between −0.35V and −0.6V. The coverage was coincident with that inferred from the (√3×√3)R30° STM image reported by us in the same condition. The formation of zinc–oxianion (phosphate and sulfate) surface complexes by Zn upd was proposed base on the difference of complex formation constants among the related zinc–anion complexes. Identification of the zinc–phosphate surface complex was thermodynamically carried out around pH=4 with a Nernst equation, where the shifts of Zn upd peak potential were investigated with the concentration changes of Zn2+, H2PO4−, and H+ under an imaginarily reversible condition. The formation of ZnHPO4 surface complex was concluded in the Zn upd with mono-electron transfer and explained a recent XAS analysis, which demonstrate each phosphate anion bridging three upd Zn atoms.

Influence of disodium ethylenediaminetetraacetate on zinc electrodeposition process and on the morphology, chemical composition and structure of the electrodeposits

Zinc electrodeposition on 1010 steel substrate, from an alkaline solution containing various EDTA concentrations, was investigated by cyclic voltammetry. The analysis of the voltammetric curves, showed, irrespective of EDTA concentration, the presence of a well defined pre-bulk region (region peak c0), where the Zn underpotential deposition (UPD), hydrogen evolution reaction (HER) and reduction of iron oxide compete, which was followed by region of peak c1, where Zn bulk electrodeposition (overpotential deposition (OPD)) occurred. AFM and XRF analysis of Zn electrodeposit on 1010 steel substrate produced voltammetrically in the region of peak c0 showed presence of Zn. These results corroborate those obtained by cyclic voltammetry, i.e., that Zn UPD occurred in the region of peak c0. The morphological, structural and the chemical composition characterization of the Zn electrodeposits prepared potentiostatically at −1.60V, were performed by SEM, XRD and EDS, respectively. SEM images showed that the size of Zn crystallites produced at deposition charge densities (qd) of 2.0Ccm−2 and 10.0Ccm−2 decreased in the presence of EDTA, except at 0.20M EDTA and qd 10.0Ccm−2. EDS analysis showed that incorporation of oxygen in the electrodeposits depended on both qd and EDTA concentration. XRD patterns of the electrodeposits produced indicated only phase of pure Zn, with various reflections, irrespective the presence of EDTA and qd. These electrodeposits exhibited crystallites preferentially oriented parallel to the (002) plane. Although EDTA led to morphological and chemical composition changes, it did not produce significant micro-structural changes, which could lead to different crystallographic orientations.

Kinetics of zinc and copper reduction in gluconate–sulfate solutions

RDE and LPS voltammetry together with energy-dispersive spectrometry was applied to study partial and net processes occurring at 2<pH<7 in 0.01M Cu(II) and Zn(II) solutions containing 0.01–0.05M gluconate and 0.5M Na2SO4. Simulations using material balance equations, which include stability constants of complexes and these of protonated ligands, show that Cu2+ and Zn2+ aqua-ions together with monoligand sulfate and gluconate complexes are formed. Furthermore, the formation of OH-containing ZnLOH complexes (L− is a gluconate anion) is evident at pH>5. Equilibrium potentials and partial cathodic processes in the system are arranged in the following order: Cu(II) reduction, hydrogen evolution and Zn(II) reduction.Rate of Cu(II) reduction drastically decreases with increasing pH. This process is accompanied by a strong chemisorption of gluconate with subsequent destruction and incorporation of oxygen and carbon in the deposits. Kinetics of hydrogen evolution on zinc and copper is similar. Its rate also decreases with solution pH and becomes insignificant in neutral media. Gluconic acid functions in this process as a proton donor. No significant suppression of Zn(II) reduction was observed in acidic and neutral media. The exchange current density for this process is comparatively high and amounts to 0.1mAcm−2 at pH 6.All previous regularities act upon the codeposition of copper and zinc. Zn content in brass increases with cathodic polarization over a wide region of potentials (−1.05<E<−0.5V). Significant depolarization of Zn(II) reduction (Zn underpotential deposition) is consistent with the thermodynamics of alloy formation.

On the Hybrid Glassy Carbon Electrode/OligoThiophene/Ag(NP) Interface

GC/OligoThiophene/Ag(NP) hybrid interfaces are synthesized and characterized: GC is the glassy carbon surface; OligoThiophene stands for both an ultrathin bithiophene grafted film and a 4-Br-Bithiophene grafted polymer; Ag(NP) stands for silver nanoparticles. The hybrid interface preparation involves different steps: first, the electrode surface is functionalized through a combination of electrochemically assisted grafting (under reduction regime) and polymerization (under oxidation regime); then, silver nanoparticles are chemisorbed by dipping. In particular, an ultrathin film of grafted bithiophene can be obtained by applying one cyclic voltammetry reduction cycle (GC/BT surface), while subsequent cyclic voltammetry cycling under oxidation regime yields an immobilized 4Br-Bithiophene polymer (GC/4BrBT surface). AFM and TEM images were recorded to investigate the morphology and chemical composition of the Ag(NP). Fe(II)/Fe(III) cyclic voltammetry, Zn underpotential deposition (UPD), XPS, LA-ICP-MS, and Raman techniques were exploited to characterize both the GC/OligoThiophene and GC/OligoThiophene/Ag(NP) interfaces. Theoretical calculation, at the B3LYP/6-311G** level of the theory, enabled rationalization of the electroreduction mechanism and the Raman results.

X-ray absorption spectroscopy characterization of Zn underpotential deposition on Au(1 1 1) from phosphate supporting electrolyte

Zn K-edge X-ray absorption spectroscopy (XAS) has been used to investigate the structure of Zn monolayers prepared on Au(1 1 1) electrodes via underpotential deposition (UPD) from phosphate supporting electrolyte. Theoretical modeling of the XAS data indicates that the Zn adatoms adopt a commensurate (√3 × √3)R30° ( θ sc = 0.33) adlayer structure and reside within the 3-fold hollow sites of the Au(1 1 1) surface. Meanwhile, phosphate counter-ions co-adsorb on the UPD adlayer and bridge between the Zn adatoms in a (√3 × √3)R30° ( θ sc = 0.33) configuration, with each phosphorous atom residing above a vacant 3-fold hollow site of the Au(1 1 1). Significantly, this surface structure is invariant between the electrochemical potential for UPD adlayer formation and the onset of bulk Zn electrodeposition. Analysis of the Zn K-edge absorption onset also presents the possibility that the Zn adatoms do not fully discharge during the process of UPD, which had been proposed in prior voltammetric studies of the phosphate/Zn(UPD)/Au(1 1 1) system.

Electrodeposition of ZnTe Compound Semiconductors from Aqueous Solution

ZnTe compound semiconductors were synthesized in acidic aqueous solution using a pulsed current electrodeposition technique. The optimum condition to obtain ZnTe deposits was determined by the cathodic polarization curves measured at a wide potential range. During the co-deposition of Zn and Te, under potential deposition (UPD) of Zn was observed. Increasing the solution temperature up to 353 K, UPD of Zn was promoted by the formation of Zn(OH)2. Crystal phase, structure and chemical composition of electrodeposited ZnTe was controlled by the solution composition and electrolysis condition. The band gap energy of ZnTe films annealed at 573 K was close to 2.26 eV.

Features of Zinc Monolayer Electrocrystallization on an Iron Electrode from a Zincate Solution

The process of Zn monolayer electrocrystallization on an iron electrode from a zincate electrolyte including the transfer from Zn underpotential deposition (UPD) to Zn phase growth under supersaturation conditions (OPD) has been studied by the galvanostatic potential transient method. In the OPD region, an analysis of potential transients E(t) has been carried out on the basis of the conception of summation of the charge transfer and crystallization overpotentials. OPD of a Zn monolayer from both the pure electrolyte and one containing an inhibiting additive of polymeric tetraalkylammonium salt does not involve nucleation and has been interpreted as development of growth sites formed on a Zn-Fe alloy surface under UPD conditions. An assumption concerning inheritance of peculiarities of Zn intercalation into the Fe crystal lattice by the charge transfer and crystallization stages of Zn monolayer growth during the UPD-OPD transfer has been strengthened.

Effects of SiC and Al2O3 particles on the electrodeposition of Zn, Co and ZnCo. I. Electrodeposition in the absence of SiC and Al2O3

Electrodeposition of Zn, Co and ZnCo from acid sulfate solutions onto steel was investigated in this first part of a study of the effects of SiC or Al2O3 particles on these processes and the formation of ZnCo–SiC and ZnCo–Al2O3 electrocomposites. Zn electrodeposition shows a well-defined pre-bulk region, where the hydrogen evolution reaction (HER) and Zn underpotential deposition (upd) compete. Zn bulk electrodeposition begins with primary nucleation and diffusion-controlled growth, strongly dependent on conditions favoring previous Zn upd against HER. It is assumed that this first bulk process takes place over the upd Zn. Zn bulk electrodeposition is followed by secondary nucleation and growth. Co electrodeposition begins with a slow $$ {\text{Co}}_{{({\text{aq}})}}^{2 + } $$ reduction in parallel with HER, followed by a faster $$ {\text{Co}}_{{({\text{aq}})}}^{2 + } $$ reduction. $$ {\text{Zn}}_{{({\text{aq}})}}^{2 + } $$ strongly hinders the initial $$ {\text{Co}}_{{({\text{aq}})}}^{2 + } $$ reduction. The ZnCo and Zn electrodeposition curves are initially similar, retaining features of pre-bulk and bulk Zn electrodeposition.

Electrodeposition of Cobalt in an Ionic Liquid Electrolyte at Ambient Temperature

AbstractThe codeposition behavior of Co and Zn in an ionic liquid was investigated. In the cyclic voltammogram of a ZnCl2‐EMIC‐CoCl2 ionic liquid, three reduction peaks appeared at 250 mV (peak c1), 50 mV (peak c2) and −200 mV (peak c3) (vs. Zn2+/Zn). According to the component analysis by means of EDS (energy disperse spectroscopy), peaks c1, c2 and c3 correspond to the electrodeposition of Co, the underpotential deposition of Zn on the electrodeposited Co coating and the codeposition of Co‐Zn alloy, respectively. The potentiostatic deposition showed that the electrodeposited coating of high‐pure Co was obtained when the cathodic potential was controlled at 100 mV (vs. Zn/Zn2+). The electrodeposition was carried out at a galvanostatic mode, and when the current density was controlled at about 85 µA/cm2, the electrodeposited coating of high‐pure Co was also obtained. Studies on the mechanism of codeposition of Co and Zn showed that the electrodeposition process of Co and the underpotential deposition process of Zn on the electrodeposited Co coating were all diffusion controlled.

Electrochemical studies on Zn deposition and dissolution in sulphate electrolyte

The electrochemical deposition and dissolution of Zn on Pt electrode in sulphate electrolyte was investigated by electrochemical methods in an attempt to contribute to the better understanding of the more complex Zn–Cr alloy electrodeposition process. A decrease of the Zn electrolyte pH (from 5.4 to 1.0) so as to minimise/avoid the formation of hydroxo-products of Cr in the electrolyte for deposition of alloy coatings decreases the current efficiency for the Zn reaction, but the rate of the cathode reaction increases significantly due to intense hydrogen evolution. The results of the investigations in Zn electrolytes with pH 1.0–1.6 indicate that Zn bulk deposition is preceded by hydrogen evolution, stepwise Zn underpotential deposition (UPD) and formation of a Zn–Pt alloy. Hydrogen evolution from H2O starts in the potential range of Zn bulk deposition. Data obtained from the electrochemical quartz crystal microbalance (EQCM) measurements support the assumption that electrochemical deposition of Zn proceeds at potentials more positive than the reversible potential of Zn. Anodic potentiodynamic curves for galvanostatically and potentiostatically deposited Zn layers provide indirect evidence about the dissolution of Zn from an alloy with the Pt substrate. The presumed potential of co-deposition of Cr (−1.9 V vs. Hg/Hg2SO4) is reached at a current density of about 300 mA cm−2.

Electrodeposition behavior of nickel and nickel–zinc alloys from the zinc chloride-1-ethyl-3-methylimidazolium chloride low temperature molten salt

The electrodeposition of nickel and nickel–zinc alloys was investigated at polycrystalline tungsten electrode in the zinc chloride-1-ethyl-3-methylimidazolium chloride molten salt. Although nickel(II) chloride dissolved easily into the pure chloride-rich 1-ethyl-3-methylimidazolium chloride ionic melt, metallic nickel could not be obtained by electrochemical reduction of this solution. The addition of zinc chloride to this solution shifted the reduction of nickel(II) to more positive potential making the electrodeposition of nickel possible. The electrodeposition of nickel, however, requires an overpotential driven nucleation process. Dense and compact nickel deposits with good adherence could be prepared by controlling the deposition potential. X-ray powder diffraction measurements indicated the presence of crystalline nickel deposits. Non-anomalous electrodeposition of nickel–zinc alloys was achieved through the underpotential deposition of zinc on the deposited nickel at a potential more negative than that of the deposition of nickel. X-ray powder diffraction and energy-dispersive spectrometry measurements of the electrodeposits indicated that the composition and the phase types of the nickel–zinc alloys are dependent on the deposition potential. For the Ni–Zn alloy deposits prepared by underpotential deposition of Zn on Ni, the Zn content in the Ni–Zn was always less than 50 atom%.

Effect of Cl − ions and benzylideneacetone/ethanol on the underpotential deposition of zinc in acidic media: cyclic voltammetry and EQCM studies

The influence of chloride ions and a benzylideneacetone (BDA)/ethanol (EtOH) mixture on the underpotential deposition (UPD) of Zn 2+ ions on Pt electrodes in acidic media was investigated by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). In the potential region of the UPD of H and Zn, the surface coverage of Zn adatoms on Pt was evaluated based on the correspondence between charge and mass for several different solutions. In the absence of Cl − ions and BDA/EtOH, the maximum surface coverage of the Zn deposited by UPD was 0.29. In addition, in the presence of Cl − ions, the UPD of Zn 2+ ions occurred simultaneously with the adsorption of Cl −, and the presence of Cl − did not modify the quantity of Zn deposited by UPD. In the presence of Cl − ions and BDA/EtOH, the maximum surface coverage of the Zn deposited by UPD was 0.16. The partial inhibition of the UPD of Zn 2+ ions is associated with the adsorption of BDA/EtOH or products of the decomposition of BDA/EtOH during the UPD process.

Use of Underpotential Deposition for Evaluation of Overpotential Deposition Kinetics of Reactive Metals

The underpotential deposition (UPD) of Zn onto Pt is shown to produce an electrode surface which is suitable for the evaluation of Zn overpotential kinetics. The UPD of Zn onto polycrystalline Pt was characterized in acidic and neutral sulfate solutions using voltammetric charge measurements and X-ray photoelectron spectroscopy. The charge density for UPD Zn deposition on platinum from neutral sulfate solution was estimated to be consistent with a monolayer. The decrease in evolution rates provided further evidence of the formation of Zn UPD layer. Evidence for the formation of a Zn-Pt alloy, resulting from polarization of the Pt electrode at a potential between the Zn UPD and overpotential deposition potentials is also presented. The alloy was oxidized at the same potential as the Pt substrate, illustrating the large interaction between Zn and Pt due to the small crystallographic misfit. The alloy also decreased evolution rates, relative to the Pt substrate. The use of such a modified substrate for measurement of kinetic parameters for metal deposition is described and the results obtained are shown to compare favorably with the literature values. © 2003 The Electrochemical Society. All rights reserved.

Voltammetric and rotating ring-disk studies of the influence of anions in the underpotential deposition of zinc on platinum

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.