Photoelectrochemical Conversion of Carbon Dioxide to Alcohols: Formation of Carbon-Based Fuels Via Carbon Bond Formation

In 2008, we reported1 the photoelectrochemical reduction of CO2 in an aqueous electrolyte at a p-GaP interface, demonstrating that pyridinium efficiently catalyzed the multielectron reduction of CO2 to methanol. This result represented the first report that CO2 could be reduced to methanol in a purely light driven system. In other words, this was the first example that one could store solar energy as a methanol fuel using a semiconductor based system. Further, the reduction by 6-electrons and 6-protons in near quantitative yield was unprecedented. The catalytic activity of pyridinium ran contrary to the standard thinking that CO2 reduction would best be achieved using a multielectron charge transfer reagent pyridinium is a one-electron, oneproton reagent. Thus, a major focus of our AFOSR research has been to develop an energetic and mechanistic understanding of this pyridinium catalyzed process as well as to expand this chemistry to other semiconductors, catalysts and electrolytes with the aim of increasing the available product distribution. The work reported here involved the activities of three postdoctoral fellows and two graduate students producing four papers of which three are either published or in press. Several undergraduate researchers also supported the project.