Reductive Electropolymerization of a Vinyl-containing Poly-pyridyl Complex on Glassy Carbon and Fluorine-doped Tin Oxide Electrodes

The overall goal of the following experiment is to demonstrate a generalized electro polymerization procedure for attaching redox active compounds to electrode surfaces. This is achieved by synthesizing molecules that attach polymer realizable functional groups to the Redox active center in order to build larger monomeric compounds capable of polymerization. As a second step, the newly synthesized redox active monomeric compounds are placed in an electrolytic solution in a carefully controlled electrochemical cell environment, which prepares the monomers for electro polymerization attempts.

Next, the monomers are subjected to standard electrochemical experimental procedures in order to induce electro polymerization at the surface of the electrode. The results show whether or not stable electro polymers surface modified electrodes are produced based on follow-up cyclic vol telemetry experiments, and fresh electrolyte solution absent of the monomer precursor and UV vis spectroscopy of film modified fluorine, doped tin oxide, or FTO slides. The main advantage of this technique over existing methods like phosphonate or car carboxylate metal oxide electrode surface absorption is that electro polymers are not absorbed to electrode surfaces through easily hydrolyzed covalent bonds, but rather precipitation.

This makes electro polymers a viable substrate material operating on electrode surfaces over a wide pH range, and can be placed on a number of electroactive substrates. This method can help answer key questions in the solar fuels field, like can we use modified electrodes to absorb and convert light energy into electrical energy? And can we use modified electrodes to perform electric catalytic conversions of abundant small molecules and to stored energy?

Generally speaking, this method allows us to learn about fundamental differences between freely diffusing and surface attached inorganic and organ metallic compounds. Generally, individuals new to this method might struggle to obtain reproducible results because of the numerous experimental factors that can affect the success of electro polymerizing and attaching compounds to electrode surfaces. That is assuming that the monomers intrinsic properties do not prevent surface absorption.

First place, 0.969 grams of tetra and butyl ammonium hexa fluoro phosphate in a 25 milliliter flame dried volumetric flask. Then add dry acetyl nitrile to bring the flask to volume place, 0.0049 grams of previously prepared compound one in a dry four gram vial and add four milliliters of the tetra and butyl ammonium hexa fluoro phosphate stock solution. Following this transfer, 3.5 to four milliliters of the resulting red orange colored electrolytic solution into the central compartment of a three compartment cell.

With each compartment separated by a medium porosity glass fret, quickly fill the outer compartments of the three compartment cell to an equal heus, the central compartment stalk solution with some of the remaining dry 0.1 molar tetra and butyl ammonium hexa fluoro phosphate solution to prevent leakage to the outer compartments. At this point, cut a slit into three rubber SEPTA and guide a thin POLYTETRAFLUOROETHYLENE or PTFE tube through each slit. Slide the silver, silver nitrate reference electrode through one of the septa.

Then place the reference electrode PTFE tube in one of the outer compartments and seal the compartment with the septum. After guiding the platinum wire gauze counter electrode through a different septum, place the platinum wire PTFE tube in one of the outer compartments and seal the compartment with the septum. Guide a freshly polished three millimeter glassy carbon electrode through the remaining septum and place it such that the electrode is suspended in the solution.

For an FTO slide guide a wire connected to an alligator clip through the septum and clamp the slide with the alligator clip. Then place the slide in the solution, making sure that the conductive side is perpendicular to the counter electrode When submerged. Next, collect a UV vis spectrum of the FTO slide by placing the slide in a position in the beam path of the spectrometer that has been predetermined to ensure consistency.

Following this, connect one end of the tigon tubing to the nitrogen supply and connect the other end to a gas washer containing aceto nitrile. After cutting another piece of tigon tubing, connect one end to the outflowing acetyl nitrile washed nitrogen, and connect the other end to a four-way splitter. Once the PTFE tubes have been connected to the three remaining connections of the four-way splitter, submerge the PTFE tubes into the solutions in each of the compartments and turn on the flow of nitrogen such that a rapid bubbling of the solution commences.

After deaerating the solution for five to 10 minutes, pull the PTFE tubes just above the surface of the solution, leaving the flow of nitrogen on in order to keep a positive pressure of inert gas on the system and to prevent solution convection caused by bubbling. To perform the electrochemical experiments, connect electrodes from the potential stat to the appropriate electrodes in the three compartment cell. Perform a cyclic vol telemetry or cv, experiment with the following parameters.

When the CV experiment is complete, remove the working electrode from the polymerization solution and gently rinse the surface of the electrode with an acetyl nitrile squirt bottle to remove any remaining monomer solution. At this point, place the rinsed working electrode in an electrochemical cell containing a freshly prepared solution of 0.1 molar tetra and butyl ammonium hexa fluoro phosphate in acetyl nitrile, a counter electrode and a reference electrode. Perform a CV experiment with the following parameters.

Integrate the charge under the anodic and cathodic peaks for the absorbed electro polymer ruthenium three, two, couple, and average the charge under the anodic and cathodic peaks. Then determine the surface coverage using the following equation. Next place the FTO slide in the predetermined position in front of the UV vis sample holder, such that the beam path passes through the colored film.

Finally, subtract the spectrum obtained for the FTO spectrum that was collected for that particular slide prior to electro polymerization. From the spectrum of the film on FTO in order to produce an absorption spectrum for the film itself. The first cycle of the electro polymer growth experiment with compound one produces a volt.

Graham roughly resembling that which is expected for a ruthenium solution of similar concentration, but upon successive cycles, increasingly enhanced currents are observed. This phenomenon is due to the summation of the current for the monomer in solution and that of the electro polymer film that is deposited from the previous cycle past the ligand centered reduction waves. The pink trace is the first cycle after reductive electro polymerization of compound one, while the blue trace is the second cycle and the remaining third to 15th cycles are in black.

The red arrows indicate decreasing current while the green arrows indicate an increase. Electro polymerization on FTO follows roughly the same trends as glassy carbon, but with the added benefit of larger surface areas and transparency. The UV vis spectrum for the FTO slide is subtracted from the electro polymer coated FTO to give the spectrum of the film alone.

DUVV spectrum of compound one is overlaid for comparison. Once mastered, this technique can be done in one to two hours if it is performed properly. While attempting This procedure, it's important to remember that the experimental setup is critical for consistent and continued reproducibility.

Stringently drying the electrolytic solution, exclusion of oxygen, strict placement of electrodes in three compartment cells, utilizing different electrochemical techniques and many other procedures may be required for reproducible results. After watching this video, you should have a good understanding of how to perform preliminary experiments to evaluate the ability of a compound to undergo electro polymerization and to preliminarily probe its stability on any number of electrode surfaces, solvent conditions, and phs.