1. STSM @ Department of Chemistry, University of Bath
Electrochemistry of Ferrocene Decorated Cellulose Nanocrystal – Gold Nanoparticle Composite Films
Department of Chemistry, University of Bath
Sam Eyley, Frank Marken, Wim Thielemans

2. Outline Introduction Previous work Aims Preparation
Electrochemical measurements
Conclusions
Future work

3. Previously
S. Eyley, S. Shariki, S. E. C. Dale, S. Bending, F. Marken, W. Thielemans, Langmuir, 2012, 28,
Cellulose nanocrystals with grafted with ferrocene via azide-alkyne cycloaddition
Resulting nanocrystals showed charge diffusion along CNCs
CV – confirm ferrocenyl
EIS – 45° line
Warburg diffusion
𝐷 𝑎𝑝𝑝 = 10 −19 𝑚 2 𝑠 −1
Bottleneck at CNC-CNC contacts?
Also determined from scan rate dependence of peak current in CV

4. Aim Solve low diffusion coefficient
Improve contacts by addition of AuNPs
Wire up ferrocene centres on Fc-g-CNCs
Increase in ferrocene signal
Improved diffusion coefficient

5. Preparation of electrodes
Premixed suspension
Layer by layer
Kapton film

6. Initial testing - CV
Confirm performance of Fc-g-CNCs is in-line with previous data
CV performed in 0.1 M KNO3
SCE reference
Pt counter
CV peak on initial cycle not reported previously
After first cycle shape as reported previously for “thin-film regime”
Reversible potential – 0.35 V vs SCE
Remember to introduce CV

7. Initial testing - EIS
Sample shows higher than 45° phase indicating non-ideal diffusion
Film heterogeneity
System most closely modelled by a series combination of resistor and constant phase element
𝑍=𝑅+ 1 𝑗𝜔 𝛼 𝐶
Detect performance improvement via signal enhancement in CV

8. Premixed Fc-g-CNC:AuNP electrodes
Electrodes prepared with varying ratios of AuNP to Fc-g-CNC
𝑋 𝐴𝑢 =0, 1 6 , 1 5 , 1 4 , 1 3 , 1 2
Peak cathodic (Faradaic) current for ferrocene - 𝑖 𝐹
Capacitive current - 𝑖 𝑐
2 𝑖 𝑐
𝑖 𝐹

9. Premixed Fc-g-CNC:AuNP electrodes
Electrodes prepared with varying ratios of AuNP to Fc-g-CNC
𝑋 𝐴𝑢 =0, 1 6 , 1 5 , 1 4 , 1 3 , 1 2
Peak cathodic (Faradaic) current for ferrocene - 𝑖 𝐹
Capacitive current - 𝑖 𝑐
Decrease in Faradaic current with increase in Au
Increase in capacitive current
Large experimental errors
2 𝑖 𝑐
𝑖 𝐹

10. Does impedance spectroscopy give a better idea?
All premixed systems show behaviour associated with a series circuit of a resistor and a constant phase element
Same as Fc-g-CNCs alone
Non-ideal diffusion
No trend in phase of CPE
Overall premixed films offer poorer performance than Fc-g-CNCs alone

11. Layer by layer electrodes: CV
Electrodes produced by alternating layers of 0.7 μg AuNPs and 5.6 μg Fc-g-CNCs
Addition of one layer of AuNPs to one layer of Fc-g-CNCs
Enhanced ferrocene signal
Enhancement diminished after two layers
Capacitance higher for gold containing films

12. Layer by layer electrodes: EIS (1)
Layering of Fc-g-CNCs without gold
Unusual behaviour on some samples – 2 time constants
Systems modelled as two parallel series of a resistor and constant phase element
𝑍 𝑛 = 𝑅 𝑛 𝑗𝜔 𝛼 𝑛
1 𝑍 = 𝑛= 𝑍 𝑛
Only for 2 and 3 layers of Fc-g-CNCs
Poor contact between Fc-g-CNC layers?

13. Layer by layer electrodes: EIS (2)
Addition of gold between layers does not result in a coherent change in impedance data
Heterogeneous deposition?
Further analysis of this data required to extract diffusion coefficients
Possible solution is “anomalous diffusion” model suggested by Bisquert and Compte
𝑍 𝐷 = 𝑍 𝐷 (0) 𝜏 𝛾 2 coth 𝑗𝜔𝜏 𝛾 2
gamma – anomalous diffusion exponent
Tau – diffusion time constant
If we say restricted diffusion, must have a physical meaning
J. Bisquert, A. Compte, J. Electroanal. Chem., 2001, 499,

14. Conclusions
Ferrocene decorated cellulose nanocrystal gold nanoparticle composite based electrodes were successfully created by drop coating
Performance of Fc-g-CNCs was different to previously reported
Non-ideal diffusion indicative of poor film homogeneity
Premixed Fc-g-CNC:AuNP films exhibited the worst performance
Loss of ferrocene signal associated with an increase in gold content
Layer by layer films showed some enhancement with addition of gold nanoparticles, but only for thin films
Addition of gold was associated with an increase in capacitive current in all cases
Impedance data on layer by layer films was inconsistent, probably due to heterogeneity in film deposition

15. Future work SEM of coated electrodes to analyse electrode structure
Application of anomalous diffusion model to impedance data
Must have physical basis - SEM
Optimization of coating of electrode to minimize film heterogeneity

16. Acknowledgements University of Bath, UK Frank Marken (Host)
Barak Aaronson
Elena Madrid
KU Leuven, BE
Wim Thielemans