UF-SEC a User-Friendly SpectroElectrochemical Cell

for UV-Vis, NIR and IR measurement

F. Fabrizi de Biani,a P. Mugnai,b A. Pellissier,c

a Dipartimento Biotecnologie Chimica e Farmacia, University of Siena, Via A. Moro 2, 53100, Siena, Italy

bLab-o-Mak, Via S. Nallo 5, 53019 Castelnuovo Berardenga (SI), Italy c Bio-Logic Science Instruments, 1 Rue de l'Europe, 38640 Claix, France

fabrizi@unisi.it

for

Structural changes of an electroactive species during an electrochemical reaction not always can be determined from the electroanalytical technique alone, while the combination of two techniques based on very different phenomena, like electrochemistry and spectroscopy, has revealed to be able to answer this and many other questions about the chemistry of inorganic, organic and biological molecules. Virtually, all the spectroscopic methods can be coupled with many different electrochemical techniques, anyway, absorption spectroscopy in the UV-Vis and IR range are, by far, the more widely diffused in spectroelectrochemical techniques.

The Heineman prototype [1] of an Optically Transparent Thin Layer Electrochemical cell (OTTLE cell) was very smart in its minimalism: a gold minigrid, used as the optically transparent electrode, was sandwiched between two glass slides with an adhesive material serving also as spacer. The cell was then dip into the sample solution and filled by suction. The open bottom allowed contact with sample reservoir solution and the reference and auxiliary electrodes.

Prototype of the OTTLE cell designed by Heineman.

Years after, this prototype has been redesigned and a simple, robust, air-tight and versatile thin layer cell has been obtained by Hartl et al. [2]

The UFS-SEC (User-Friendly-Spacer for UV-Vis, NIR and IR SpectroElectrochemical Cell) is the OTTLE cell 3.0 Since the electrodes-containing spacer is what converts a common semi-demountable IR cell in a SEC cell, we have designed the UFS set (spacer+frame), which fits with the more popular demountable or semi-demountable IR cell and can be used with every kind of windows. A dedicated frame, carved in Teflon®, works as windows- and spacer-aligner, at the same time, and the spacer can be easily removed together with its electrodes-set and plugs.

The cell can be placed directly in a bench spectrometer. Alternatively, optical fibres can be used to connect the cell to light source and to the spectrometer

The UFS – SEC set has been conceived to perform thin-layer spectroelectrochemistry. In such finite diffusion conditions, a thin solution layer ( 0.2 mm) adjacent to the electrode is confined by the cell walls, so that the cell thickness is smaller than the diffusion layer and the mass transfer can be ignored. The most significant virtue of thin-layer cells is the absence of diffusion and the rapidity with which the electroactive species can be exhaustively electrolysed. The dropping to zero of the current flow following the peak in the current potential plot is a characteristic behaviour of thin-layer cells, indicating exhaustive electrolysis of the reactant and minimal diffusion effects in the thin-layer cell.

The most significant virtue of thin-layer cells (finite diffusion conditions) is the rapidity with which the electroactive species can be completely electrolysed (few seconds): this way, the interfering reactant absorption is not observed, while in semi-infinite diffusion controlled methods the time scale may be inconveniently slow.

An IR cell with the UF set

Spectroelectrochemical cell with optical fibres

--- first cycle, ... second cycle.

The UF Spacer UV-vis SEC of ferrocene/ferrocenium redox change. Concentration: 5 mM in CH2Cl2/NBu4PF6 (0.2 M); starting potential 150 mV, step: +50 mV, 1 min.

CVA of ferrocene/ferrocenium (7 mM in CH2Cl2/NBu4PF6 0.2 M). Absorbance at 620 nm has been monitored during a cyclic potential scan (10 mV/s) in a IR cell equipped with UFS and optical fibers.

Cathodic/anodic area ratio.

Ferrocene in CH2Cl2/NBu4PF6 (0.2 M); scan rate 5 mV/s.

You can freely choose your preferred windows according to the specific spectral region you want to explore: by using the UFS set you can easily access both windows, which can be cleaned, replaced or removed for safe storage, without any difficulty. You can easily clean or substitute the electrode set: the UFS spacer can be quickly removed from the frame to be cleaned and even sonicated. You can freely choose Au or Pt as your preferred material for the working electrode, avoiding foolish of the electrodes due to undesired absorption phenomena: the UFS spacer can be quickly removed from the frame to be substituted.

This makes the UF- SEC set the more cost-effective and versatile solution for highly efficient UV-vis, NIR and IR spectroelectrochemistry

Due to the subtleness of the wires, electrodes soldering to the plugs is possibly the more fragile part of every spectroelectrochemical cell, for this reason in the UFS the soldering nuggets connecting the silver wires to the plugs are well protected by a cover. Anyway, they are also easily accessible just unscrewing a couple of spins. This way you can simply check the possible presence of a broken contact.

UF-SEC

IR Spectroelectrochemistry during [Pt6(m-PtBu2)4(CO)6]2+ reduction. Concentration: 9 mM in CH2Cl2/NBu4PF6 [3]

Performance

REFERENCES

1. R. W. Murray, W. R. Heineman, G. W. O’Dom, Anal. Chem., (1967), 39, 1666.

2. M. Krejčik, M. Daněk and F. Hartl, J. Electroanal. Chem. (1991) 317, 179.

3. P. Leoni, F. Marchetti, C. Bonaccorsi, F. Fabrizi de Biani, L. Marchetti, P. Zanello, Chem. Eur. J. (2008) 14, 847

See also: F. Fabrizi de Biani and A. Pellissier EC-Lab - Application Note #52 06/03/2014 on http://www.bio-logic.info