Estudo da eletrocristalização de Ni e Ni-P sobre ultramicroeletrodo de platina

Eguiluz, Katlin I.B.; Avaca, Luís Alberto; Barin, Cláudia Smaniotto

doi:10.1590/s0100-40422008000500042

Cited by 1 publication

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“…UMEs generate low currents, allowing for measurements of high current density while minimizing ohmic ( iR ) losses and electrochemical cell RC time constant delays that can distort the current response at macroscale (area of ≈1 cm 2 ) electrodes. − High mass transport associated with the nearly hemispherical diffusional field of UME disks enables steady-state conditions to be attained readily − without distortions from forced hydrodynamics that can disturb evolving surface chemistry such as local H 2 O structure or gel formation. , This diffusional field is also more uniform than that associated with free convection at quiescent macroscale electrodes. The dimensions of UMEs are amenable for studying nucleation mechanisms and growth morphology, − ,− where the electrode size is commensurate with that of the growing crystals, as well as optical microscopy, where the entire UME area and its diffusion layer can be imaged, − providing spatial–temporal insight into electrochemical phase transformations. Thus, we took advantage of the optical contrast between Au and Ni to follow the electrodeposition of Ni.…”

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confidence: 99%

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

Ritzert

Moffat

2016

J. Phys. Chem. C

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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.

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