Kinetics and growth modes of quasi-2d silver branched electrodeposits produced in the presence of a supporting electrolyte

Ultramicroelectrode Studies of Self-Terminated Nickel Electrodeposition and Nickel Hydroxide Formation upon Water Reduction

The interaction between electrodeposition of Ni and electrolyte breakdown, namely the hydrogen evolution reaction (HER) via H₃O⁺ and H₂O reduction, was investigated under well-defined mass transport conditions using ultramicroelectrodes (UME's) coupled with optical imaging, generation/collection scanning electrochemical microscopy (G/C-SECM), and preliminary microscale pH measurements. For 5 mmol/L NiCl₂ + 0.1 mol/L NaCl, pH 3.0, electrolytes, the voltammetric current at modest overpotentials, i.e., between -0.6 V and -1.4 V vs. Ag/AgCl, was distributed between metal deposition and H₃O⁺ reduction, with both reactions reaching mass transport limited current values. At more negative potentials, an unusual sharp current spike appeared upon the onset of H₂O reduction that was accompanied by a transient increase in H₂ production. The peak potential of the current spike was a function of both [Ni(H₂O)₆]²⁺_(aq) concentration and pH. The sharp rise in current was ascribed to the onset of autocatalytic H₂O reduction, where electrochemically generated OH^- species induce heterogeneous nucleation of Ni(OH)_2(ads) islands, the perimeter of which is reportedly active for H₂O reduction. As the layer coalesces, further metal deposition is quenched while H₂O reduction continues albeit at a decreased rate as fewer of the most reactive sites, e.g., Ni/Ni(OH)₂ island edges, are available. At potentials below -1.5 V vs. Ag/AgCl, H₂O reduction is accelerated, leading to homogeneous precipitation of bulk Ni(OH)₂·xH₂O within the nearly hemispherical diffusion layer of the UME.

Silver electrodeposition on nanostructured gold: from nanodots to nanoripples

Silver nanodots and nanoripples have been grown on nanocavity-patterned polycrystalline Au templates by controlled electrodeposition. The initial step is the growth of a first continuous Ag monolayer followed by preferential deposition at nanocavities. The Ag-coated nanocavities act as preferred sites for instantaneous nucleation and growth of the three-dimensional metallic centres. By controlling the amount of deposited Ag, dots of approximately 50 nm average size and approximately 4 nm average height can be grown with spatial and size distributions dictated by the template. The dots are in a metastable state. Further Ag deposition drives the dot surface structure to nanoripple formation. Results show that electrodeposition on nanopatterned electrodes can be used to prepare a high density of nanostructures with a narrow size distribution and spatial order.

Influence of Pinning Effects on the Electrochemical Formation of Silver Patterns in Agarose-Containing Sols and Gels

The formation of silver patterns via electrolysis from aqueous silver sulfate + x% w/v agarose sol and gel media, with and without supporting electrolyte, in a quasi-two-dimensional (2D) cylindrical cell at room temperature, is utilized as a reference system to investigate the complexity of pinning effects. From pattern morphology and electrochemical data, both delocalized and localized pinning in the bulk dominate the drift of the growth front, depending on the concentration of agarose in the heterogeneous media. Delocalized pinning results from mobile, small agarose aggregates at the growth front and from their accumulation by the front drift. For gels, localized pinning comes from their own percolated structure. A depinning/pinning transition is observed in going from sols to gels. The relative contribution of diffusion and advection in mass-transport-controlled silver electrodeposition depends on the plating bath composition. On the other hand, silver ion attachment to the cathode appears to be interfered with by some screening caused by weakly adsorbed, mobile agarose aggregates at the metal surface without slowing down the rate of the electron-transfer step at the cathode. Their relative contribution of a delocalized, localized pinning and screening effect to a great extent determines the morphology and transition in the growth mode of silver patterns in both media. The analysis of charge and current transients and the corresponding silver pattern morphologies for open and dense radial patterns is made. Results are qualitatively simulated with a novel, rather simple cellular automaton algorithm.

Stability analysis of branched silver electrodeposits: solid phase growth under a marginally stable regime

The mass-transport controlled growth of silver deposits at the early stage of multiple bump formation, and when a silver single needle growth regime is attained, are investigated. Linear stability analysis as proposed by Barkey, Muller, and Tobias [J. Electrochem. Soc. 136, 2199 (1989)] is applied to kinetic mesoscale data. A reasonable correlation between the current density and the average amplitude of unstable perturbation is established.