Comparison between staircase
and linear sweep voltammetry, and presentation of a valuable alternative:
analogue current integration in Cyclic voltammetry
The staircase method for cyclic voltammetry is widely used in digital micro-processor based
instruments, because discrete steps are easier to make with digital electronics than real linear sweeps.
Moreover the electrical double layer contribution to the current, or the charging current, is reduced if
the duration of the step is sufficiently long. This results in data that can be treated as originating from
faradaic processes only. The Autolab electrochemical instruments and its software normally use the
staircase method for cyclic voltammetric measurements. True linear sweep voltammetry is available
through the optional SCANGEN module.
Figure 1, shows an example of a waveform for a staircase experiment. The moment at which the
current is measured (designated by the value of α) can be specified; for α=0.25 the current is
sampled at one quarter of the total step duration, for α=1 the current is sampled at the end of the step,
etc. In order to improve the signal to noise ratio, the sampling of the current is done during a certain
time interval, if possible during on net cycle (20 or 16.6 ms).
Waveform for staircase voltammetry.
Figure 1: Waveform for staircase voltammetry. Value of alpha denotes the moment of
When kinetic processes are studied, the difference between the staircase and the linear sweep method
is expected not to be very large. M. Seralthan and R.A. Osteryoung (J.Electroanal. Chem. 222,
69(1987)) have made a theoretical comparison between normal staircase voltammetry and linear
sweep voltammetry. They showed that similar results can be obtained when the current is measured at
the right moment during the step; for a reversible system the current should be sampled at one quarter
of the total step duration. So, for those involved in the research of electrochemical kinetics, staircase
voltammetry is a good alternative for the (true) linear sweep voltammetry.
The story is different for extremely time dependent processes like Under Potential Deposition (UPD),
Electrical double layer effects and Hydrogen adsorption on Pt. In these cases the above described
(normal) staircase method fails. This is due to the effect that these phenomena take place at the
beginning of a step and have vanished at the time the current is sampled.
Autolab instruments and software also offer a staircase method which is able to record these fast
phenomena. In this method the analogue current integrator which is present in the µAutolab, the
PGSTAT10 and the FI20-module, is used. The integrator is reset at the beginning of each step.
Subsequently, the integrated current or charge is sampled at the end of each step. By dividing the
charge value by the step duration a value for the (pseudo) current is obtained.
Since one is measuring a pseudo current with the current integration method, it is important to know
what the difference is between the integration method and the linear sweep method. The theory can be
kept rather simple if it is assumed that the electrochemical cell behaves like a linear system.
In that case the charge at the end of the step is equal to:
∆Q = ∆ E • H (t )
where H(t) is the so-called unit-step response. In case of a simple RC circuit this unit-step response is
C (1 − exp( − te / RC )
where te is the time at the end of the step. Now for large values of te, H(t) reduces to C.
The pseudo current, measured with the current integration method for a linear system now is equal to:
Ips = ∆ Q / ∆ t = ( ∆ E / ∆ t )C (1 − exp( − te / RC))
Ips = ( ∆ E / ∆ t ) H ( t )
Where ∆E/∆t is defined as the scan rate for staircase sweeps. The pseudo current is thus equal to the
scan rate multiplied by the unit-step response. It can be shown that linear sweep voltammetry yields
the same result. The formal mathematics is more complicated and also beyond the scope of this note.
So for linear electrochemical systems, linear sweep voltammetry should give the same result as the
current integration method. In the figures below, some examples of measurements are given, which
show that this is indeed true. Each figure contains a normal staircase voltammogram (SV), a staircase
voltammogram using the analogue current integration (SV-CI) and a linear sweep voltammogram
The measurements with the gold and platinum electrode have been made by Dr. Piotr Skoluda of the
A. Mickiewcz University in Poland.
Figure 2: Full CV for polycrystalline Au, measured with three different methods
Figure 2 shows a voltammogram of polycrystalline Au in perchloric acid. The three different methods
are indicated with SV(Staircase Voltammetry), LSV(true Linear Sweep Voltammetry) and SV-CI
(Staircase Voltammetry-Current Integration). Figure 3 shows the double layer region of the same
curve. It is here clearly visible that charging currents due to the double layer capacitance are
suppressed when the staircase method is used. Furthermore Linear Sweep and Current Integration
Voltammetry give the same response.
Figure 3: Same as figure 2, but zoomed into the double layer region
Figure 4 shows the voltammogram of a Pt electrode in sulphuric acid. The difference between SV and
the other two methods is clearly visible in the hydrogen adsorption region. This region is suppressed in
the case of staircase voltammetry because the hydrogen adsorption is so fast that the process is ended
before the end of the step. One therefore measures only the end of the adsorption process.
Figure 4: CV of Pt electrode in sulphuric acid. The differences between the methods are clear
Figure 5: CV for ferri/ferro measured with three different methods. SV is measured with alpha=1
For a normal kinetic process, the differences between the three methods are small, as is shown in
figure 5. Choosing the right value for α results in identical curves for all three methods (vide supra).
In Autolab instruments and software the specifications for the three different methods are as follows:
Normal Staircase Staircase using Linear sweep using
current integration SCAN-GEN module
Max. scan rate >200 V/s 5V/s 10.000V/s
Max. sampling rate 30.000/s 1.000/s 750.000/s
This short communication clearly shows the differences between three methods of cyclic voltammetry.
It may be concluded that under all investigated circumstances the current integration technique is a
valuable alternative. In case (true) linear sweeps are needed, the Autolab instruments have the
possibility of using the optional SCAN-GEN module.
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