Question

Answer the following questions about sampled-current voltammetry.

#1 describe the difference between a charging current and Faradaic current.

#2 Explain why you should wait for a few seconds before applying the voltage and measuring the current in the sampled-current voltammetry.

Answer 1

In voltammetry the total current consists of two part. The current from analyte's oxidation or reduction and a residual current.

Residual current again consists of faradaic current of trace impurities and anotherbis charging current.

Current resulting from redox reaction is called faradaic current.

The current other than faradaic current in an electrochemical cell is nonfaradaic current. Let charge of an electrode in neutral and suddenly it acquires some positive charge, anions then migrate towards that electrode and cation will migrate away. This phenomenon takes place untill positive charge of electrode and negative charge of the solution near the electrode are same. Such movement of ions and electrons are not distinguishable. This type of short lived nonfaradaic current is called charging current.

In Voltammetry , the charging current decays follows exponential curve.

But faradaic current decays as function of 1/ (time).

Rate of decay of faradaic current is slower than that of charging current.

2.

As decay of charging current is faster , that is why you have to wait some seconds so that charging current has decayed. The first current is instrumentally substracted and the time difference is plotted against applied potential. So that charging current has negligible contribution .