Question

(a) Estimate the iR drop expected in a cyclic voltammetry experiment run at 100 Vs^‐1, where a 1mm diameter disc electrode is used in a 10mM solution of ferrocene dissolved in dichloromethane. The diffusion coefficient is 2 x 10^‐5 cm² s^‐1 and the resistance between the working g and reference electrode is 600Ω.

(b) Estimate the iR drop in the same solution at the same scan rate, when a 25 um diameter microelectrode is used instead. (Assume the resistance between the working and reference electrodes remains at 600Ω).

(c) Same for 1 um diameter microelectrode.

(d) Draw a rough sketch of what the CVs in (a) and (b) might look like.

Answer 1

a. i_p = 0.4463*1*96485*0.00785*10^-6*0.00001*√(1*96485*100*2*10^-5/8.314*298)

i_p = 1.24*10^-9

i_R drop = i_p*R = 1.24*10^-9*600

i_R drop = 7.44*10^-7

b. i_p = 0.4463*1*96485*0.049*10^-6*0.00001*√(1*96485*100*2*10^-5/8.314*298)

i_p = 7.74*10^-9

i_R drop = i_p*R = 7.74*10^-9*600

i_R drop = 4.64*10^-6

c. i_p = 0.4463*1*96485*0.785*10^-12*0.00001*√(1*96485*100*2*10^-5/8.314*298)

i_p = 1.23*10^-10

i_R drop = i_p*R = 1.23*10^-10*600

i_R drop = 7.38*10^-8