230
A. Gupta and C. Srivastava
texture of coatings [5–9]. These secondary additions act as an additional nucleation site for the reducing metal ion/complexes during the electrodeposition and thus
they provide additional control over the rate of deposition. It has been reported that
graphene or GO generally get absorbed over the previously formed growth centres
and thus, allow the nucleation and growth of less favourable atomic planes [10].
Because of presence of oxygen containing groups over the GO sheets, GO exhibits
easier dispersibility in aqueous-based electrolytes as compared to CNT and graphene
[11, 12].
Nucleation and growth mechanism of coatings can be studied by chronoamperometry (CA) method where deposition is carried out at an externally applied
potential. CA tests generate a current–time transient (CTT) which is mathematically modelled to reveal the deposition kinetic parameters involved in the nucleation
process. Additionally, the understanding of free energy required for nucleation and
the critical nucleus size can also be developed based on the data obtained from CA
tests. Modelling of CTT has been in an ever-developing phase with Bewick et al.
[13] being the pioneers in the field. They came up with the model corresponding to
two-dimensional lattice incorporation (2D li ) of adatoms to form subsequent layers.
In 1983, Scharifker and Hills [14] proposed the two kinds of three-dimensional
nucleation and growth (3D nu ) models: instantaneous and progressive nucleation and
growth. A generalized 3D nu model was proposed in 1984 by Scharifker and Mostany
[15, 16] (SM model) which assumed diffusion-controlled nucleation and growth
process with impingement of overlapping diffusion zones which slows down the
overall growth rates at longer durations. This generalized SM model has been modified with addition of simultaneously occurring reactions and with consideration of
other assumptions [17–20].
Understanding of nucleation and growth mechanism is an integral part of electrodeposition. In the present study, the nucleation and growth mechanism of tin and
cobalt over the GO sheets has been studied using the cyclic voltammetry (CV) and
CA techniques. The quintessential kinetic parameters involved in nucleation process
like number density of active nucleation sites (N 0 ), nucleation rate constant (A), diffusion coefficient (D) have been calculated using the model developed for the CTTs.
The classical and atomistic theory of nucleation aided in calculation of Gibb’s free
energy involved in formation of stable nucleus and the size of critical nucleus. An
understanding has been developed on how GO, as a substrate, affects the deposition
kinetics of metal/alloy coatings.
Methods and Materials
Substrate Preparation
GO synthesis was performed using the modified Hummer’s method [21] the details
of which is provided in earlier reports [22]. A 1 mg/ml solution of GO in deionized
A. Gupta and C. Srivastava
texture of coatings [5–9]. These secondary additions act as an additional nucleation site for the reducing metal ion/complexes during the electrodeposition and thus
they provide additional control over the rate of deposition. It has been reported that
graphene or GO generally get absorbed over the previously formed growth centres
and thus, allow the nucleation and growth of less favourable atomic planes [10].
Because of presence of oxygen containing groups over the GO sheets, GO exhibits
easier dispersibility in aqueous-based electrolytes as compared to CNT and graphene
[11, 12].
Nucleation and growth mechanism of coatings can be studied by chronoamperometry (CA) method where deposition is carried out at an externally applied
potential. CA tests generate a current–time transient (CTT) which is mathematically modelled to reveal the deposition kinetic parameters involved in the nucleation
process. Additionally, the understanding of free energy required for nucleation and
the critical nucleus size can also be developed based on the data obtained from CA
tests. Modelling of CTT has been in an ever-developing phase with Bewick et al.
[13] being the pioneers in the field. They came up with the model corresponding to
two-dimensional lattice incorporation (2D li ) of adatoms to form subsequent layers.
In 1983, Scharifker and Hills [14] proposed the two kinds of three-dimensional
nucleation and growth (3D nu ) models: instantaneous and progressive nucleation and
growth. A generalized 3D nu model was proposed in 1984 by Scharifker and Mostany
[15, 16] (SM model) which assumed diffusion-controlled nucleation and growth
process with impingement of overlapping diffusion zones which slows down the
overall growth rates at longer durations. This generalized SM model has been modified with addition of simultaneously occurring reactions and with consideration of
other assumptions [17–20].
Understanding of nucleation and growth mechanism is an integral part of electrodeposition. In the present study, the nucleation and growth mechanism of tin and
cobalt over the GO sheets has been studied using the cyclic voltammetry (CV) and
CA techniques. The quintessential kinetic parameters involved in nucleation process
like number density of active nucleation sites (N 0 ), nucleation rate constant (A), diffusion coefficient (D) have been calculated using the model developed for the CTTs.
The classical and atomistic theory of nucleation aided in calculation of Gibb’s free
energy involved in formation of stable nucleus and the size of critical nucleus. An
understanding has been developed on how GO, as a substrate, affects the deposition
kinetics of metal/alloy coatings.
Methods and Materials
Substrate Preparation
GO synthesis was performed using the modified Hummer’s method [21] the details
of which is provided in earlier reports [22]. A 1 mg/ml solution of GO in deionized