Carbon dioxide concentrations in the atmosphere are relentlessly increasing due to fossil fuel combustion which is significantly contributing to global warming. In addition to the global warming implications of fossil fuel usage, supplies of liquid fuels critical for modern life will become more scarce physically and economically. To combat these dual problems of CO₂ sequestration and liquid fuel shortages, renewable energy could be stored in the form of liquid fuels with CO₂ as the feedstock. A significant barrier to this process is the lack of an efficient, fast and robust catalyst for CO₂ reduction, especially to higher order products like methanol, ethanol, or butanol. The Bocarsly group seeks to uncover the mechanism of CO₂ electrochemical- and photoelectrochemical-reduction by aromatic amines.

In 1992 it was reported by the Bocarsly group that pyridinium could catalyze the reduction of CO₂ to methanol at 30% yield at hydrogenated palladium electrodes.¹ This chemistry was subsequently extended to platinum metal electrodes, also resulting in methanol formation at about 30% yield. In 2004, a mechanism for the reduction of CO₂ at platinum was proposed as follows, including both surface and solution based catalytic steps as well as a key intermediate, the reduced pyridinium-CO₂ radical adduct:

The evidence for this mechanism includes the detection of formic acid and formaldehyde as well as methanol in solutions following electrolysis, cyclic voltammetry with electrochemical modeling of pyridinium in the presence and absence of CO₂ as well as possible intermediates (formic acid and formaldehyde) and pressure and temperature studies.^2,3

The chemistry has been expanded to other metal and semiconductor electrodes, including demonstration of 96% faradaic efficiency for methanol formation at p-GaP electrodes at an underpotential of -0.32 V.⁴ Pyridinium derivatives have also been found to catalyze the reduction of CO₂ to products including isopropanol and ethanol.

Current work in the lab is focused on further mechanistic understanding of CO₂ reduction, especially the C-C bond formation observed in higher order reduced products. Work continues on novel catalysts and surfaces, with particular attention to observing reaction intermediates in situ using FTIR, EPR, and Raman spectroscopies. Electrochemical techniques including cyclic voltammetry and bulk electrolysis are used frequently in the lab as well as surface science techniques such as XPS, XRD, SEM, and TEM. It is hoped that greater understanding of the parameters controlling catalysis will lead to the design of more efficient, robust and fast catalysts for CO₂ reduction, as well as further the knowledge of CO₂ activation and C-O bond breakage, and C-C and C-H bond formation.

1. Seshadri, G.; Lin, C.; Bocarsly, A. B. A new homogeneous electrocatalyst for the reduction of carbon dioxide to methanol at low overpotential. J. Electroanal. Chem. 1994, 372, 145-50.

2. Barton, C. E.; Lakkaraju, P. S.; Rampulla, D. M.; Morris, A. J.; Abelev, E.; Bocarsly, A. B. Using a One-Electron Shuttle for the Multielectron Reduction of CO₂ to Methanol: Kinetic, Mechanistic, and Structural Insights. J. Am. Chem. Soc. 2010, 132.

3. Morris, A. J.; McGibbon, R. T.; Bocarsly, A. B. Electrocatalytic carbon dioxide activation: The rate-determining step of pyridinium-catalyzed CO₂ reduction. ChemSusChem 2011, 4, 191-196.

4. Barton, E. E.; Rampulla, D. M.; Bocarsly, A. B. Selective Solar-Driven Reduction of CO₂ to Methanol Using a Catalyzed p-GaP Based Photoelectrochemical Cell. J. Am. Chem. Soc. 2008, 130, 6342-6344.