(414c) Design of Autonomous Multifunctional GaN:ZnO Based Photocatalysts for Artificial Photosynthesis

The global reliance on fossil fuels as a 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 exploits full solar spectrum conversion to split water and reduce CO₂ at moderate temperatures 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 for CO₂ reduction based on co-catalyst composition, oxidation state, and CO₂:H₂ feed ratio. In addition, an increase in activity of CO₂ reduction was 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.