Electrochemical response of ferricyanide/ferrocyanide redox couple
Formation of Au-BSA colloidal solution
There were a number of errors from yesterday's work
- for pot/galv, SENSE was left unconnected; must be connected to same electrode as working
- reference electrode must be in contact with measured solution (salt bridge, frit, or direct)
- BSA stock solution was 17.7 μM, not 17.7 mM (Au stock still 2.7 mM)
- Ratio for solution & fibers is 60Au:1BSA & 170Au:1BSA, NOT BSA:Au!!
- Ac buffer does not lead to colloidal solution (may not be acidic enough); use water!
- Solutions need to be heated for 4 hrs in oven (2 hrs in block), not 30 min!!
- CV & EIS of ferricyanide using CG working electrode
- Began with GC WE, GC CE, & Ag/AgCl(sat KCl) external reference --> no signal
- GC WE, GC CE, & Pd wire same soln reference --> CV generated!
- 2nd & third reduction peaks at 0.7 & 1.0 V --> used -0.5 to 0.5 V range!
- switched to Pd CE --> measured at 10 mV/s, 50 mV/s, 100 mV/s, & 500 mV/s
- used same setup to measure EIS from 100 kHz to 100 mHz
- switched to "2pt", using CG working & sense, Pd counter & reference, remeasured EIS
- Preparation of BSA - AU colloidal solution
- 2.5 mL HAc/NaAc + 500 μL BSA + 200 μL HAuCl4 in glass test tube
- heated in oven at 78C for 3 hr --> colorless solution w/ purplish precipitate (left in oven overnight)
- 1.5 mL water + 500 μL BSA + 200 μL HAuCl4 in glass test tube
- transfered 900 μL of 2nd soln to plastic cone & poured remainder into glass cone
- placed cones in heating block at 80C --> after 1 hr, plastic changing to pink; glass still colorless
CV of K3Fe(CN)6 with KNO3 as the supporting electrolyte
- The redox couple is K3Fe(CN)6 / K4Fe(CN)6
- The potential of the forward (cathodic or reductive) peak and the reverse (anodic or oxidative) peak is constant as the scan rate is changed. Therefore, this redox couple is reversible.
- The formal redox potential for this couple equals 0.5(Epf + Epr) = 0.5(0.19 V + 0.13 V) = 0.16 V
- n (the number of electrons transfered during the redox reaction) can be calculated from the separation between peaks:
- ΔEp = 59 mV / n
- (0.19 V - 0.13 V) = 0.06 V = 0.059 V / n
- Therefore, n = 1.
- Finally, the diffusion coefficient for the electrolyte can be calculated from,
- ip = (2.69e+05)ACn3/2D1/2v1/2
- 9.24e-05 A = (2.69e+05)*(0.35 cm2)*(2.00 mol/cm3)*(1)1.5*D0.5*(0.100 V/s)0.5
- D0.5 = 1.22e+06 cm/s0.5
- D = 1.48e+12 cm2/s
EIS of K3Fe(CN)6 with KNO3 as the supporting electrolyte
Data was collected. However, the data will be meaningless; electrodes were not aligned next to each other, so the electron path is not linear. In addition, two different electrodes were used. Finally, the supporting electrolyte will add to the conductivity. On the bright side, the plot is smooth, which is expected for a solution.
BSA - Au Colloidal Solution
After three hours in heating block, both plastic & glass vials were dark pink solutions. They were left in the heating block overnight, but the heat was turned off. UV/VIS will be measured on a later date.