Carbon Dioxide and Alkanes as Electron-sink and Source in a Solar Nanocell: towards Tandem Photosynthesis of Carbon Monoxide and Methanol

Lead Research Organisation: University of York
Department Name: Chemistry

Abstract

A major solar energy challenge is the goal of artificial synthesis in which sunlight is used to generate fuels or high energy chemicals. Natural photosynthesis uses solar energy to generate dioxygen and carbohydrates from carbon dioxide and water, but the targets of artificial photosynthesis can be more diverse. Our vision is to create a solar nano-device which will drive the coupled photo-conversion of methane and carbon dioxide into methanol and carbon monoxide respectively. This challenging target differs fundamentally from the familiar one of splitting water into hydrogen and oxygen. Our target offers products both on the oxidation and the reduction sides that are significant fuels or feedstocks. The photocatalytic reduction of CO2 and oxidation of alkanes represent long-standing goals of great complexity, but we base our concepts on well-established principles. We break down the goals into individual components, each of which is highly challenging within its own right and delivery of each would constitute a major breakthrough. The challenges will be met by a team of scientists, integrated across the four centres of Manchester, Nottingham, York and Norwich, who lead teams with expertise in photophysics, nanoscience, photochemistry, electrochemistry and synthesis. Thus these researchers will seek to establish the science required to underpin technologies that will allow the conversion of abundant and environmentally damaging feedstocks into products of high economic value by constructing a new class of solar device capable of driving green chemical reactions.
 
Description The energy of sunlight is used by plants to form starch and sugars by using carbon dioxide from the atmosphere and, at the same time, generating oxygen gas. Why can't we do the same? The goal of artificial photosynthesis is to design an analogous process that yields a fuel that can be burnt or a compound that can be used to form other materials, such as polymers. We call such products "solar fuels". Our consortium addressed this problem from the point of view of the chemical reduction (analogous to reducing carbon dioxide in photosynthesis) and the chemical oxidation (analogous to producing oxygen from water in photosynthesis). The task of the York chemists was to design and synthesise molecules that catalysed the reduction of carbon dioxide with the aid of visible light. Our design incorporated a dye molecule and a catalytic centre in the same molecule. The dye absorbs the light and transfers an electron to the catalytic centre where carbon dioxide is reduced to carbon monoxide. The latter can be used as a fuel or as a source for making petroleum or polymers. Our design succeeded in making carbon monoxide from carbon dioxide with very low energy light but the number of molecules of product formed per molecule of catalyst was low. We found that the results could be substantially improved by using separate dye and catalytic molecules rather than incorporating them into one molecule, the "dyad". This result opens the way to optimising the choice of dye and catalyst without the laborious synthesis of the dyad. At a more detailed level, the dye was composed of a molecule closely related to natural chlorophyll but containing zinc or palladium at the centre instead of magnesium. The catalyst centre contained the unusual metal rhenium and an electron accepting component. In the dyads the two halves were linked by an amide bond like in a protein. The liaison with other members of the consortium was very productive. We collaborated extensively with Professor Michael George (Nottingham) to measure the speed of electron transfer from the dye to the catalytic centre and the speed of electron return using his equipment for time-resolved infrared spectroscopy. These experiments were very valuable for understanding our results and improving our designs. We also collaborated with Professor Wendy Flavell (Manchester) and Professor Chris Pickett (East Anglia) to provide dye molecules that were adapted to bind to nanoparticles. The regular progress meetings of the consortium were extremely stimulating for the York members of the team met and enabled them to grasp the connections between the different components of the project. The major results from York have now been published. I was active in several initiatives for encouraging research into solar fuels and spoke about the project at conferences and at university seminars. Together with other members of the consortium, the York group contributed to a major outreach event, the Royal Society Summer Exhibition in 2011 (http://royalsociety.org/summer-science/2011/solar-nanotech/). The event had more than 13000 visitors and our stand was thronged with people throughout.
Exploitation Route to devlop new methods of photocatlysis for solar fuels
Sectors Energy
 
Description The findings have been used for scientific engagement
First Year Of Impact 2011
Sector Culture, Heritage, Museums and Collections
Impact Types Societal
 
Description Fundacion Caja Madrid
Amount £12,000 (GBP)
Funding ID Master's Studentship 
Organisation Caja Madrid Foundation 
Sector Charity/Non Profit
Country Spain
Start 10/2011 
End 09/2012
 
Description University of York
Amount £65,000 (GBP)
Funding ID DTA studentship 
Organisation University of York 
Sector Academic/University
Country United Kingdom
Start 10/2009 
End 03/2013