Photoreduction of Carbon Dioxide

The 21st century has begun with the realization that long term solutions are needed to replace our dependence on fossil fuels that dominated the 20th century.  Much attention has been placed on the sun as the future energy source. For electricity and power, much emphasis has been placed on photovoltaic cells and together with many other alternatives, technologies are in place and developing to replace fossil fuel based power plants.  For fuel, needed for transportation and also in many industrial sectors, our progress is less advanced and significant scientific hurdles need to be overcome. In essence, in order to utilize the solar energy as a fuel it must be captured and then stored.  Storage can come in many forms, for example, batteries to store electricity, hydrogen from water splitting and biofuels through growth of aquatic or terrestrial flora and algae. In our group we are investigating an additional option, the reduction of carbon dioxide to carbon-based fuels with solar energy using chemical catalysis. This option, if proved to be viable has the attraction that the huge carbon-based infrastructure already in place need not be replaced.
In the research in our group we are considering a less studied catalytic chemical approach to the recycling of CO2 to fuel. More specifically, we are interested in the direct use of solar photochemical energy whereby the photoenergy is initially stored as chemical energy in the two-electron reduced product, carbon monoxide (CO). Although combustion of CO can yield ~67 Kcal/mol, perhaps more importantly liquid fuels would be available from CO using known technologies that include (i) formation of H2 from CO and therefore syn gas via the water-gas shift (WGS) reaction, (ii) methanol synthesis for CO and H2, and (iii) further possible methanol transformations or use of syn gas for Fischer-Tropsch processes. For CO2 photoreduction we are considering two catalytic motifs designed to operate using visible light under ambient or nearly ambient reaction conditions:

  1. A coupling of a water splitting reaction where an O2 evolving photocatalytic semiconductor that also yields electron and protons is coupled to CO2 to CO reduction catalyst.
  2. The development of a catalyst for the direct photocatalytic splitting of CO2 to CO and O2.