Gong Luo

In this microreview, the importance of electrochemical phase formation is outlined. Further, the establishment of current transition during electrochemical nucleation and growth is explored. First, the microreaction kinetic process of electrocrystallisation and the rate-controlling steps of electrodeposition are carefully discussed. Then, the current transient formulation under electrochemical polarisation-controlled electrocrystallisation is summarised. Finally, a summary of the process for calculating the current transient formulation of nucleation and growth under diffusion-controlled electrocrystallisation is explained in detail.

A brief review is given on the current transition of the electrodeposition of materials by a mechanism of nucleation followed by diffusion-controlled growth. A short historical background to study the nucleation and growth by diffusion-controlled electrocrystallization is provided. Then, an outline of the major potentiostatic current transient modeling is given, with some comments on their relative merits. Finally, a summary of the current transition functions of nucleation and growth under diffusion-controlled electrocrystallization is given including the theoretical models that have been recently applied.

A novel cyanide-free electrolyte was used in electrodepositing Au/Co–Au nano-multilayers. Firstly, an optimised electrolyte for Au–Co alloy electrodeposition was obtained from orthogonal experiments. The effect of current density and potential values on the deposited composition was investigated. Results showed that low current density and over-potential value promoted Au deposition. A large current density and high over-potential value resulted in high cobalt concentration. The co-deposition of gold and cobalt in this study system was canonical. When the electrode potential was positive (−0.6 V, −0.7 V vs. saturated calomel electrode (SCE)), only gold was deposited; when the potential was negative (−0.8 V vs. SCE), gold and cobalt were co-deposited. Using an optimised cyanide-free electrolyte produced Au/94.07 at% Co–Au multi-layers with a gold layer of approximately 20 nm and a 94.07 at% Co–Au alloy layer of approximately 90 nm in the 5,5-dimethylhydantoin-containing, cyanide-free system.

Chronoamperometry was used to investigate phase transformations at the early stage of electrodeposition under potentiostatic stimuli. Whilst electrodeposition mostly occurs under galvanostatic stimuli, this work provides a new in situ description using chronopotentiometry to analyse phase transformations during electrodeposition. With theoretical Ohm's law electro-relationship formula derivation, a non-dimensional plot between (ΔE_min/ΔE_T)² and t/t_m was established similar to (I_t/I_max)² vs. t/t_m in the SH model. The non-dimensional plots were verified by the chronopotentiometry curve during gold electrodeposition. This work provides a new method of investigating phase transformation using chronopotentiometry during electrodeposition.

A novel cyanide-free electrolyte is reported for electrodepositing bright gold layers from a solution of both Au( iii ) and Au( i ).