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Normal Pulse Voltammetry (NPV)

Last Updated: 3/6/19 by Support

ARTICLE TAGS
  • AfterMath NPV,
  • current vs. potential,
  • normal pulse voltammetry,
  • NPV
Capable Potentiostats
AFTERMATH LINKS
Article Contents/Section Navigation
  1. Technique Overview
  2. Fundamental Equations
  3. Experimental Setup in AfterMath
    1. Basic Tab
    2. Advanced Tab
    3. Ranges, Filters, and Post Experiment Conditions Tab
  4. Sample Experiment
  5. Example Applications
  6. References

1Technique Overview

Normal Pulse Voltammetry (NPV) is a derivative technique of Normal Pulse Polarography (NPP).  NPP is a technique that was traditionally used with Dropping Mercury Electrodes and Static Mercury Dropping Electrodes. The waveform for the two techniques is the same; however, it is appropriate to use the term “Normal Pulse Voltammetry” when referring to the application of the waveform to nonpolarographic electrodes.
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2Fundamental Equations

Consider the reaction
 
O + ne^- \rightleftharpoons R
 
where O is reduced in a one-electron reaction to R with formal potential E^0.  The application of a baseline potential should be sufficiently positive of E^0 such that no faradaic current flows.  After a period of time ({\tau}'), typically 100 - 5000 ms, the potential of the working electrode is stepped to a more negative value for a period of time.  The total time from the application of the baseline potential through the application of the potential pulse is {\tau}.
The potential pulse is incrementally increased with each cycle. As the potential of the working electrode approaches E^0 faradaic current flows due to the reduction of O to R.  Upon the application of the baseline potential in the next cycle, R is oxidized back to O. When the potential of the working electrode gets sufficiently negative of E^0, O is reduced to R at a maximum rate and the current levels off to a plateau The magnitude of this current plateau is given by
\displaystyle i_{d,NPV} = \frac{nFAD_O^{1/2}C_O^*}{{\pi}^{1/2}({\tau}-{\tau}')^{1/2}}
where n is the number of electrons, F is Faraday's Constant (96,485 \; C/mol), A is the electrode area (cm^2), D is the diffusion coefficient(cm^2/s), C is the concentration (mol/cm^3) and {\tau}' and {\tau} are as described above.
As seen in the Typical Results section, RNPV gives the same wave shape but not the same current. These results are analogous to DPSCA where the current during the forward pulse is different than the current in the reverse pulse. Here in RNPV, the baseline potential is such that  O is being reduced to  R at a maximum rate. As the potential of the working electrode approaches  E^0 a faradaic current flows due to the oxidation of  R to  O . Once the potential of the working electrode is sufficiently positive of  E^0 ,  R is being oxidized at a maximum rate and the current plateaus. The magnitude of this current plateau is give by
$latex i_{d,RPV} = \frac{nFAD_O^{1/2}C_O^*}{{\pi}^{1/2}}\left[{\frac{1}{({\tau}-{\tau}')^{1/2}}}-{\frac{1}{{\tau}^{1/2}}}\right]&s=3$
where the parameters are as described above. Notice that in the Typical Results section, there is a slight anodic current flowing at the beginning of the experiment. The magnitude of this current is given by the equation
$latex i_{d,DC} = \frac{nFAD_O^{1/2}C_O^*}{{\pi}^{1/2}{\tau}^{1/2}}&s=3$
where the parameters are as described above. The magnitude of this current is the difference between the NPV and RNPV currents.
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3Experimental Setup in AfterMath

To perform a normal pulse voltammetry experiment in AfterMath, choose Normal Pulse Voltammetry (NPV) from the Experiments menu (see Figure 1).
 
Normal Pulse Voltammetry (NPV) Experiment Menu Selection in AfterMath

Figure 1. Normal Pulse Voltammetry (NPV) Experiment Menu Selection in AfterMath

 
Doing so creates an entry within the archive, called NPV Parameters. In the right pane of the AfterMath application, several tabs will be shown (see Figure 2).
 
Normal Pulse Voltammetry (NPV) Experiment Basic Tab

Figure 2. Normal Pulse Voltammetry (NPV) Experiment Basic Tab

 
Continue reading for detailed information about the fields on each unique tab.
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3.1Basic Tab

3.2Advanced Tab

3.3Ranges, Filters, and Post Experiment Conditions Tab

4Sample Experiment

5Example Applications

6References

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