SIEMENS

If Dr. Osman Ahmed had his way, every building on earth could become a tree. Ahmed, who heads Research and Innovation at Siemens’ Building Technologies division in Buffalo Grove, Illinois, would be happy to see "green" buildings everywhere - metaphorically speaking, that is. "If we apply the principles of photosynthesis to facade coatings, every building could convert carbon dioxide (CO₂) in the air into other carbon compounds, such as methanol," he says when describing his "Building as a tree" vision, which he is promoting together with Prof. Maximilian Fleischer from Siemens Corporate Technology (CT) in Munich, Germany. Such coatings should contain nanoscale pigment particles that help to capture sunlight in the same way as the chlorophyll in plants, as well as titanium dioxide, which is also found in wall coatings and toothpaste and, like the silicon of a solar cell, can convert sunlight into electricity. "The coatings can be green like a leaf, but also orange, pink or gray," Ahmed adds.

Solar energy captured this way could be used to convert CO₂ into fuels like methanol that would then be conveyed through a system of capillary pipes into a tank inside a building. From there it could be transported to other locations or used on site if needed to produce heat and electricity. Ahmed is particularly impressed with the method’s tremendous potential. "By harnessing just a quarter of the solar energy falling on buildings in the United States, a major portion of the carbon dioxide emitted in the U.S. could be reused," he says.

But achieving as much as 25 percent efficiency in such systems is still just a vision - albeit an attractive one. The German Chemical Industry Association (VCI) considers synthetic photosynthesis to be "one of the most attractive variants" for the reuse of CO₂ "in the long term." In fact, shimmering red dye-titanium dioxide cells that convert sunlight into electricity already exist. They are being manufactured by Australian solar cell company Dyesol for deployment on roofs and have an efficiency of ten percent. And Welsh firm G24 Innovations has been producing such solar cells as plasticpackaged electricity suppliers on a roll since late 2009. Using sunlight to convert CO₂ and water into methanol and oxygen, however, is still a matter for scientists conducting basic research. Their studies focus on finding suitable and stable catalysts for the chemical reaction.

Synthetic photosynthesis is one of many options when it comes to reusing climate-damaging CO₂ rather than just blowing it into the atmosphere or burying it underground. After all, everything that is produced today using fossil raw materials - from fuels to plastics - could theoretically also be produced from carbon dioxide. Experts representing science, business and industry took a closer look at the most promising ideas for the recycling of CO₂ at a workshop in Bonn in the fall of 2009. The colloquium was organized by Siemens and the German Federal Ministry of Education and Research (BMBF). "Our primary goal was to illustrate the potential for realization of the various strategies for using CO₂," says Dr. Jochen Kölzer of Siemens CT. The BMBF alone will invest €100 million over the next five years in research and development in this field.

Biofuels from Algae. One of the methods discussed at the Bonn workshop was algaebased CO₂ recycling. "Algae use photosynthesis to build new biomass from the carbon atoms in carbon dioxide, and they do so five to ten times more efficiently than land plants," reports Dr. Manfred Baldauf, a chemist at Siemens CT in Erlangen.