# Differential and Integrated Capacitance of the Pt/solution Inter phase

Question

When a power supply brings an electrode in an ionic solution to a potential versus a reference electrode, then the electrode surface and adjacent layer of solution store charge like two plates of a parallel plate capacitor. The inner potential drop between electrode surface and adjacent layer of solution is like the voltage between the parallel plates, V, and the capacitance C is given by

C = q/V    ---------- (1)

And taking the derivative with respect to time gives the voltage/current relationship

I(t) = C dV(t)/ dt  ----------- (2)

For a Pt disk (that is, the working electrode) in aqueous 0.1M KCl has its potential scanned at a scan rate (dV(t)/dt) of 50, 100, 200, 500 mV/sec (see figure). For the 500 mV/sec scan (black line) calculate

1. the differential capacitance of the Pt/solution interphase at 0.3 volt using equation 2.
2. the integral capacitance of the Pt/solution interphase between 0.2 and 0.4 volt using equ 1.

Summary

This question belongs to physics and discusses about Pt disk working electrode and to determine the differential capacitance of the Pt/solution interphase.

Total word count: 30

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• Giuseppe

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