The global reliance on fossil fuels as the primary energy source is unsustainable due to massive CO2 emissions. An extremely appealing solution is to develop Artificial Photosynthesis (AP) technologies that utilize solar energy to drive the conversion of water and negatively valued CO2 into positively valued chemicals and fuels.  Previous research in this field has focused on photocatalytic AP reactions at near ambient conditions, high temperature dissociation of H2O and CO2 through metal-oxide looping, or photoelectrochemical approaches. These approaches are limited by low rates, high temperatures, and/or complicated and expensive process design. We will discuss an approach that has the potential to exploit full solar spectrum conversion to split water and reduce CO2 at moderate temperature on autonomous multifunctional materials. The hypothesis driving this work is that a single material can be designed that utilizes high-energy photons to drive the endothermic water splitting reaction and low energy photons to heat the catalyst and drive the exothermic CO2 reduction process. Multifunctional catalysts are designed by combining autonomous GaN and ZnO based water-splitting photocatalysts with co-catalysts for thermocatalytic CO2 reduction.We have explored the effect of co-catalyst metal type and oxidation state, CO2:H2 ratio, reaction temperature, and light intensity on thermocatalytic CO2 reduction. We tested various GaN:ZnO supported methanation co-catalysts, Ni, Ru, Rh and their oxide counterparts, for their ability to drive CO2 reduction and suppress oxidation back reactions. Results have shown a difference in catalytic activity and selectivity between metal types and oxidation states as well as CO2:H2 ratio in the CO2 hydrogenation reaction. In addition, an increase in activity of CO2 hydrogenation has been observed in the presence of light at elevated temperatures. These results will be discussed in the context of designing an overall H2O and CO2 conversion process based on autonomous, multifunctional materials.

Compositional study of GaN:ZnO supported artificial photosynthesis co-catalysts

247th National Meeting (2014)

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