January 24, 2014
Simultaneous reduction of carbon-dioxide (CO2) and water using sunlight has been an important step in life cycle on earth. This single reaction performed by plants in an energetically frugal, albeit inefficient, process allows simultaneous balance of CO2 gas and energy harvesting from the primary source of energy on earth, the sun. Several strategies are being investigated currently for converting sunlight into viable renewable source of energy, to address the growing emission of greenhouse gases and depleting sources of cheap energy for burgeoning human population. Developing an efficient artificial photosynthetic process to carry out simultaneous reduction of CO2 and water can address this issue of rising level of greenhouse gas emission and provide an alternative source of renewable energy. While several research groups have been trying to develop titanium dioxide (TiO2) nanoparticle catalysts, using expensive metals (like platinum) as chemical dopants for obtaining high catalytic activity, lack of insights into energetic pathways governing multi-electron reduction of CO2 into selective fuels has impeded further research.
Researchers from Assistant Professor Prashant Nagpal’s group recently utilized measurements of electronic density of states (DOS) of nanoparticle catalysts, to identify energy levels responsible for photocatalytic reduction of CO2-water in an artificial photosynthetic process. They introduced these desired states in their nanoparticle catalysts, using dopants or semiconductor nanocrystals, and the designed catalysts were used for reduction of CO2 selectively into hydrocarbons, alcohols, or aldehydes. Using their new design strategy, they also demonstrated a new composite nanocatalyst which shows highest selectivity for hydrocarbon solar fuels (ethane here, >70% selectivity), and high catalytic activity. They also demonstrated that their inexpensive nanocatalyst (4.3% internal quantum efficiency) outperforms platinum-doped TiO2nanoparticles (2.1%), using a small solar concentrator (4 X solar radiation). Their study can have important implications for development of new inexpensive photocatalysts with tuned activity and selectivity.
This research was recently published in the journal Nano Letters. Along with Prashant Nagpal, the study was conducted by Chemical Engineering postdoctoral associate Vivek Singh and graduate students Ignacio Beltran (co-first author) and Josep Ribot. Prashant’s recent NSF CAREER Award will support further development of other nanoparticle catalysts for making selective solar fuels.