C.T.J. Low, F.C. Walsh / Electrochimica Acta 53 (2008) 5280–5286
5285
Fig. 2(a)showsthe linearsweep voltammetry of tin electrode-
posited under controlled rotation speeds from 0.014 mol dm
the onset of hydrogen evolution to more negative potentials. The
hydrogen evolution also occurred at more positive potentials
with the electrode rotation speed but remained constant at a sat-
urated hydroquinone concentration. This is comparable to the
addition of sorbitol to a tin alkaline bath which also shifted the
hydrogen evolution reaction to more negative potentials [21].
The changes in the limiting current density with storage time
are shown in Fig. 5(a) in the absence of hydroquinone and in
−
3
SnSO4 and 12.5 vol.% methanesulfonic acid in the absence of
hydroquinone. Electrode rotation speed from 200 to 4800 rpm
were investigated; voltammetry in the background electrolyte
was also carried out. The electrode potential was swept from 0
−
1
to −1.0 V vs. Ag|AgCl at 16 mV s . Regions of charge transfer,
mixed (charge transfer and mass transport) and mass transport
controlled deposition of tin were clearly defined. As the rotation
speedsincreased, thecurrentdensityforthemixedcontrolregion
increased and the potential window for complete mass transport
control narrowed, leading to hydrogen evolution at less nega-
tive potentials. The determination of limiting current density in
the complete mass transport control region was obtained using
plots of E/j against 1/j [20]. Fig. 2(b) shows such a plot; three
distinctive regions can be identified: region A is the mixed con-
trol region, B is the complete mass transport control region and
C is the region of hydrogen evolution reaction. Limiting current
density was obtained from the mid-value between the minimum
and maximum peaks [22].
−3
Fig. 5(b) in the presence of 0.005 mol dm hydroquinone in the
electrolyte. In the absence of hydroquinone, the limiting current
density reduced significantly over the duration of the studies.
Fig. 5(c) shows the decrease in the limiting current density with
logarithm of storage time. After 512 h, there was an approxi-
mately 67% decrease in the size of limiting current density for
tin deposition in the absence of hydroquinone. In the presence of
−
3
0.005, 0.05 and 0.5 mol dm hydroquinone in the electrolyte,
only 9–13% decrease in the limiting current density was found
after a time of 512 h.
4. Summary
Fig. 3(a) shows the voltammetry of tin electrodeposited in the
presence of various hydroquinone concentrations. The addition
of hydroquinone to the electrolyte results in a single limit-
ing plateau for tin deposition from an acid methanesulfonate
electrolyte. The presence of hydroquinone lengthened the com-
pletely mass transport controlled region for tin deposition and
displaced hydrogen evolution to more negative potentials. It also
reduced the limiting current density for metal deposition, which
may be associated with the adsorption of hydroquinone onto the
electrode surface. This relationship was similar to that observed
in Fig. 1(b) under static conditions.
(1) Electrodeposition of tin onto and anodic stripping of
tin from a copper surface have been studied at static
and rotating disc electrodes, in the presence of hydro-
quinone as an antioxidant. The electrolyte conditions were
−
3
0.014 mol dm
acid (1.93 mol dm MSA) at 296 K.
SnSO4 and 12.5 vol.% methanesulfonic
−
3
(2) The Levich and Randles-Sevcik equations were used to
evaluate the mass transport characteristics of tin deposi-
tion from the electrolyte at various potential sweep rates,
electrode rotation speeds and hydroquinone concentrations.
The diffusion coefficient of stannous ions was found to be
Under complete mass transport controlled of tin deposition
at a smooth RDE, the Levich equation:
−
6
2
−1
6.5 × 10 cm s in the absence of hydroquinone in the
tin acidic electrolyte.
2
/3 −1/6
1/2
jL = 0.62zFD
ν
cω
(7)
(3) Tin was electrodeposited onto a copper surface, over a
narrow potential range, under charge transfer and mixed
control, with a well-defined mass transport controlled
region. Voltammetry showed a negligible charge transfer
overpotential. Under static electrode conditions, a single
reduction and a single oxidation peak were observed in the
absence and presence of hydroquinone. At a rotating disc
electrode, a single limiting current plateau was seen, corre-
sponding to the two-electron reduction of stannous ion to
metallic tin.
(4) Electrolyte stability was monitored with storage time via
changes in the peak and limiting current densities. In the
absence of hydroquinone, a significant loss in these prop-
erties is observed. The addition of hydroquinone to the
electrolyte reduced the rate of stannous ion oxidation.
(5) The limiting current density for tin deposition has been
determined via a graphical analysis method. The region of
complete mass transport control and the onset of hydrogen
evolution were dependent on the electrode rotation speed
and hydroquinone concentration. When the molar concen-
tration ratios of hydroquinone to stannous ion changed from
0.36 to 3.6, the complete mass transport control region was
lengthened and the hydrogen evolution was shifted to more
can be used to determine the diffusion coefficient of stannous
ions [9–11]. Here, jL is the limiting current density, ν is the
kinematic viscosity of the electrolyte, ω is the electrode rotation
speed, c is the bulk concentration of stannous ions, D is the
diffusion coefficient of stannous ions, F is the Faraday constant
and z is the number of electrons transferred.
Fig. 3(b)showsaplotoflimitingcurrentdensity vs. thesquare
root of electrode rotation speed at various hydroquinone concen-
trations, determined via the approach shown in Fig. 2(b). This
technique allowed the limiting current density to be measured
to a reasonable degree of accuracy due to the obvious minimum
and maximum point in the plot. The electrode potential was suf-
ficiently negative that the tin electrodeposition was under mass
transport control and there was a negligible contribution from
the secondary reaction of hydrogen evolution.
For freshly prepared electrolytes, Fig. 4(a) shows the region
of complete mass transport control. Region B in Fig. 2(b)
increased with hydroquinone concentration, decreased with the
electrode rotation speed and remained constant at a saturated
hydroquinone concentration. Fig. 4(b) shows a similar relation-
shipwheretheadditionofhydroquinonetotheelectrolyteshifted
Low
