Conclusions

1
Nichole Squair and Robert J. LeSuer Department of Chemistry and Physics, Chicago State University, Chicago, IL 60628
Using scanning electrochemical microscopy to
investigate electron-transfer processes in dye
sensitized solar cells.
i-t amperometric curves
74 of anthocyanin pigment from raspberries is
cyanidin-3-sophoroside
Spanos, Wrolstad. J. Assoc. Off. Anal. Chem.
1987, 70, 1036.
Current response at UME following 5 s
illumination of anthocyanin/TiO2 film

• Incentives for organic dyes
• Amenable to systematic functionalization
• Wealth of knowledge regarding photosensitive
  compounds
• Cost
• Methodology development
• Easy-to-fabricate DSC
• Cherepy et al. J. Phys. Chem. B. 1997, 101, 9342.

Influence of substrate illumination difficult to
observe with SECM-LSV

• Detection of Fe(III)(CN)63- generated at DSC
  illuminated for 5 s.
• Approximate distances based on fit of approach
  curve to insulator feedback
• Theory for kinetic control of Fe(III)(CN)63-
  generated at DSC from 1 mM Fe(II)(CN)64- in 0.1 M
  KNO3.
• keff 1.5x10-5 cm s-1, D0 7.1x10-6 cm2 s-1 5
  ?m radius Pt tip
• Flattening of experimental i-t curves may be due
  to diffusion through TiO2 film.

Methods

• 5 mM ferrocenemethanol in 0.1 M KCl
• 5 ?m radius Pt UME tip (RG 5)
• LSV obtained at tip/substrate gap of 1 ?m
• Quantitative analysis of approach curves
  complicated by large substrate (linear diffusion)

Scanning Electrochemical Microscopy
Dye Sensitized Solar Cell
Fe(II)?Fe(III) at UME
Fe(III)?Fe(II) at UME
Illumination decreases Fe(II) near surface.
Fe(III) production at surface is slow
Sample concentration profile showing linear
diffusion of Fe(III) from substrate and
consumption at UME tip
SECM investigation of a DSC

• Ultramicroelectrode (UME) brought close to ( 1
  um) a large electrode
• Negative feedback
• Blocking effect dominates current
• Substrate does not regenerate redox mediator
• Positive feedback
• Substrate regenerates redox mediator completely
• Mixed feedback
• Can measure reaction kinetics at substrate

Conclusions

• i-t amperometric curves appear to be most useful
  in probing photochemistry at anthocyanin-coated
  plates
• Heterogeneous electron-transfer rate very slow
• Response influence by diffusion through
  nanostructure?
• Quantitative cyclic voltammetry and approach
  curves require higher efficiency DSC system and
  optimal redox mediator.
• Future experiments include
• Use of non-aqueous electrolytes.
• Influence of redox mediator charge on
  electron-transfer process.
• Influence of anthocyanin functionalization on
  heterogeneous et process.