Electrocrystallization of Distinct Ni Nanostructures at the Ionic Liquid/Au(111) Interface:  An Electrochemical and in-Situ STM Investigation

Abstract

Electrocrystallization of Ni nanostructures has been studied at the Au(111)/ionic liquid [AlCl3−[C4mim]+Cl- (58:42) + 5 mM Ni(II)] interface by in-situ scanning tunneling microscopy, cyclovoltammetry, and chronoamperometry. In the underpotential deposition (UPD) region, a well-defined superstructure, incommensurate c(p × 2 ) structure, of adsorbed AlCl4 - layers is observed. It exists over a potential range of more than 0.35 V down to 0.15 V. Below this potential, 2D Ni phase formation sets in and a complete monolayer grows over a period of ∼800 s. In the overpotential (OPD) range, different morphologies of Ni nanoclusters have been obtained depending on the parameters of the respective electrodeposition procedures. Jumping the potential from above 0.15 V (UPD) to −0.25 V, the peak potential of bulk Ni deposition, large nearly spherical (∼10 nm diameter) Ni clusters first nucleate at the step edges of the Au(111) substrate and spread with time all over the surface. In this case, a progressive nucleation and growth mechanism with diffusion control is found. A distinct and interesting morphology is obtained, if first a complete monolayer of Ni is deposited at UPD conditions and then the potential is directly decreased to OPD values near −0.18 V. Elongated Ni clusters with a diameter of ∼10 nm and an aspect ratio of ∼2 nucleate and grow instantaneously. Most interestingly, they are all oriented in one direction which is indicative of a magnetic interaction between the Ni clusters.

Electrochemical behavior of Ni(II)/Ni in a hydrophobic amide-type room-temperature ionic liquid

“…7, the diffusion coefficient of Ni(II) was estimated to be 7.5 × 10 −8 cm 2 s −1 according to the Sand's equation [36], which was close to that from chronoamperometry. The values are smaller than those reported in chloroaluminate ionic liquid (2.8 × 10 −6 [37] and 2.1 × 10 −7 cm 2 s −1 [15]), since the viscosity of the BMPTFSA is higher than those of the chloroaluminate ionic liquids. However, the diffusion coefficient of Ni(II) is close to those of Co(II), Fe(II) and Sn(II) in BMPTFSA [33,38,39].…”

“…The electrodeposition of Ni has been mainly studied in acidic chloroaluminate or chlorozincate ionic liquids [9][10][11][12][13][14][15][16][17][18] except the choline chloride-urea eutectic [19] and the DCA − -based (DCA − : dicyanamide) ionic liquids [20]. In case of chloroaluminate or chlorozincate ionic liquids, codeposition of Al or Zn makes it difficult to obtain Ni alloys containing the metals less noble than Al or Zn.…”

The Electrode/Ionic Liquid Interface: Electric Double Layer and Metal Electrodeposition

“…However, in [BMP][N(Tf) 2 ], no obvious UPD phenomenon was observed due to strong adsorption of BMP + at the surface. [105] The UPD of both Ni [147] and Co [148] on Au(111) in [BMI]Cl-AlCl 3 also features the formation of single-atom-high islands, but the coalescence of the Co islands was not observed. [148] Zn UPD on Au(111) in [BMI]Cl-AlCl 3 proceeds with the formation of three successive monolayers.…”

“…[147] Fast potential stepping directly into the OPD region without resting in the UPD region leads to initial nucleation at the step edges, with large and nearly spherical Ni clusters with diameters of~10 nm. This is followed by subsequent nucleation all over the surface.…”

Electrochemical Behaviour of Iron in a Third‐Generation Ionic Liquid: Cyclic Voltammetry and Micromachining Investigations

“…In order to further reduce the amount of water, the IL was dried overnight at 70 °C under vacuum (10 −5 –10 −6 mbar) prior to the experiments. 1‐butyl‐3‐methylimidazolium chloride ([Bmim] + Cl − ) was prepared from 1‐chlorobutane and 1‐methylimidazole (both from Merck) and purified by recrystallization from acetonitrile as reported elsewhere 13. Appropriate amounts of [Bmim] + Cl − were mixed with [Emim] + Ntf2 − under argon atmosphere (O 2 and H 2 O concentration <1 ppm) to obtain the 15 % (w/w) [Bmim] + Cl − +[Emim] + Ntf2 − electrolyte.…”