What is the reaction of CO2 reduction in TBAH/acetonitrile?

As far as I understand, standard potential can be calculated from free Gibbs energy of a reaction. Thus, for CO2 reduction in aqueous electrolytes:

CO2 + 2H+ + 2e- -> CO + 2 H2O, E0=-0.52 V NHE (pH=7)

(literature value). Then, using Nernst equation, you can calculate E0 for the concntrations in your system.

But for acetonitrile solution, E0 might be different: either above reaction, or its free energy may not be the same.

Thanks Sergey. Yes, there is E0 value only for the aqueous solution, but not for the acetonitrile has been reported. The expected reaction is exactly what you have mentioned here. We may be able to calculate the value, but seems like it involves so much maths. I am kind of trying to estimate the turn over frequency of the catalyst from CV data using the rate equation.

The Tetra butyl Ammonium Hydroxide (TBAH) is highly alkaline in nature and is available only as aqueous solution at various concentrations to a maximum concentration of 60% and pH is about 14 in aq soln. The dissolved CO2 in acetonitrile will react with TMAH to its carbonate. We have developed electrochemical process for the production of TBAH ( upto 60%) from the respective bromides and chlorides and the process has been commercialised by Tatva Chintan Pharma Chem, ankeleswar, Gujarat.. We have learnt the properties of TBAH to some extent.

Thanks Subramanian for your information. Actually TBAH here refers to tetrabutylammonium hexafluorophosphate. So the electrolyte solution, TBAH in dry MeCN, should not be alkaline. Small amount of water is added to enhance the CO2 reduction by the transition metal catalyst via protonation.

First of all you have to remember that there is no correspondence between the thermodynamic value of the standard redox potential and the peak potential experimentally observed in solution. This is because you have a chemically irreversible process and you don't know its speed. CO2 is reduced to a several side reaction products, not only CO! If you have only CO2 in solution you reduce CO2 to [CO2]-, which have a large overpotential, that in turn quickly decomposes to several reaction products.

If you want to evaluate the standard redox potential you have to study very careful the mechanism of the electrochemical reaction, or try to avoid the associated chemical complications. However, I doubt that very fast CV scans can avoid chemical complications...

Have you seen the paper by Aaron Appel and Jim Mayer and coworkers? It addressed just this!

http://pubs.acs.org/doi/abs/10.1021/acs.inorgchem.5b02136

Sincerely,

Kyle