A voltammogram is a graph that can be drawn after an electrochemical experiment. This graph has a typical, recognizable form (Figure 1) in which the electron flow (current: I) is measured in Ampere against the potential (E) in Volt.
The typical shape of the voltammogram is due to the way in which an electrochemical experiment is usually set up. There are roughly two groups of measurements that are plotted as voltammograms: pulsed techniques and linear sweeps. We will focus here on linear sweeps.
Phases in a voltammogram
- In order to investigate the presence of a particular substance in a liquid, a potential is applied to an electrode in the liquid by means of a potentiostat. This potential is increased linearly by a fixed increase per period of time.The potential of the electrode will cause the substance to react.The initial cathodic (negative), where no reaction took place, turns into a more anodic (positive) potential. The electrode starts to draw electrons from the substance in the liquid towards itself. The curve now shows an exponentially upward trend, i.e. with increasing potential the current increases.
- After reaching the so-called redox potential, the initial exponential rise of the curve levels off. The cause being the decreasing amount of substance in front of the electrode, which also results in a lack of electrons, until eventually no electrons are left to draw close. The curve is at its highest point.
- The potential is still being increased towards anodic (positive) potentials. Still the current is decreasing , because there is less and less substance left to collect. Due to diffusion substance is transported towards the electrode. All substance that reaches the electrode is immediately converted. A further increase of potential doesn’t lead to an increase of current. The current is limited by the diffusion of new substance towards the electrode.
- The researcher no longer has any reason to further increase the potential. In case of a Cyclic Voltammetry the potential descend linearly again. This drop in potential causes the lower curve, that shows exactly the same gradient as the upper curve of the voltammogram, but then reversed. The substance, which was converted furing the anodic increase will now be reduced (receiving electrons) again.
What a voltammogram shows
A voltammogram shows the potential of the substance present in the liquid. This potential is equal to the mean of the two peaks of the voltammogram. Due to the fact that the potential of various substances is known, the results of the electrochemical experiment can be used to – in a short period of time – determine which substance is present in the liquid. Without permanently changing the liquid, that is.
Drawing a voltammogram can of course be done manually by connecting different measured points. A simpler way to create a voltammogram is by using the software usually supplied with the potentiostat used by the researcher.
Palmsens has developed various potentiostats that are supplied with their own user-friendly software. Do you prefer using your own spread sheet oftware? No problem: the data can easily be exported to it.
Voltammograms are the results of electrochemical experiments that can be performed with a potentiostat. Palmsens developed a line of attractively priced potentiostats that you can use for your own research. You can choose (among other things) from:
- EmStat: This small economical potentiostat has everything in it for conducting research grade experiments of a general nature.
- OEM EmStat: Our EmStat potentiostat is also available as an OEM potentiostat, fully applied to your specific research. In addition to the potentiostat, the software is also fully adapted to this. Please ask us about the possibilities!
- Palmsens4: This small potentiostat is also a galvanostat and EIS analyzer and can be used not only for the creation of voltammograms but also for other types of experiments in which, for example, it is not the potential of a substance that has to be demonstrated, but the present electron flow (current).