The world’s dependence on fossil fuels and nuclear power could easily become a thing of the past if someone could figure out a cost-effective and efficient process of converting the sun’s energy into a form of convenient and inexpensive fuel. While doing so may sound like a fantasy worthy of a science fiction tale, scientists are working on the process. It’s called artificial photosynthesis. Plants have been using photosynthesis for billions of years, converting sunlight into carbohydrates and oxygen.
Artificial photosynthesis and the artificial leaf
Artificial photosynthesis is so important to the generation of solar fuel technology that the U.S. Department of Energy established the Joint Center for Artificial Photosynthesis (JCAP) in 2010. It was funded with a budget of $122 million over five years. JCAP’s primary mission is the development of a renewable fuel source for the nation while reducing carbon emissions. In addition, the mission statement also says they are to “develop a manufacturable solar-fuels generator, made of Earth-abundant elements, that will use only sunlight, water, and carbon dioxide as inputs and robustly produce fuel from the sun ten times more efficiently than current crops.
Artificial photosynthesis was the basis for the development of Nocera’s artificial leaf. Basically, it is a thin rectangular object made with silicon. Sandwiched between the layers is a photovoltaic cell. The “leaf” is placed in water, and when sunlight is shone on the leaf, the inorganic materials bonded to the surface use the sun’s energy to split the water into oxygen and hydrogen via the cell. The hydrogen can actually be seen bubbling to the surface as the process takes place.
When Daniel Nocera, a professor of chemistry at Harvard University first developed the artificial leaf, infrastructure was not in place to collect, store and use the hydrogen being produced by the leaf. According to many of Nocera’s critics, he went too far and way too fast, But Nocera was not ready to give up. He theorized that it would be possible to create a liquid fuel from the artificial photosynthesis process.
The making of a liquid fuel using sunlight
In collaboration with biologists at Harvard, a gram-negative bacteria, Ralstonia eutropha was used. R. eutropha is a member of the Betaproteobacteria class of bacteria. It is found in waste water and soil, and is able to use both organic compounds and hydrogen as an energy source. Being non-pathogenic and easy to work with, R. eutropha was genetically engineered to create R. eutropha H16, making it capable of utilizing CO2 as a sole carbon source for alcohol-based liquid fuels.
The scientists needed to find out how to store solar energy when there was no sunlight. In natural photosynthesis, a natural biomass is created when sunlight meets carbon dioxide and water, but another step is needed to turn the biomass into a fuel. (For example, the added production process needed to turn corn into fuel). But the researchers used the genetically engineered bacteria, R. eutropha to skip the production process, going directly to producing fuel.
Hopefully nobody is lost yet. Here is a step by step breakdown of what happens:
1. Using the artificial leaf, water is split into oxygen and hydrogen.
2. R. eutropha absorbs the hydrogen and combines it with carbon dioxide, producing isopropanol.
3. The whole setup might look like an algae farm, except the bacteria would not need maintenance, says Nocera
“This is sort of the next step moving beyond hydrogen to make a fuel that is integratable with our current infrastructure,” Nocera, a co-author of a study that appeared in the journal Proceedings of the National Academy of Sciences Monday, told CBS News.
While Nocera’s team has been successful, there are still plenty of barriers to overcome. The big problem is improving the process so that it is efficient. So far, the team is only able to convert about one percent of the sunlight into liquid fuel. According to Nocera, they would need, at a minimum, 10 percent efficiency to meet requirements for a viable and sustainable solar fuel industry.
Artificial photosynthesis and the search for a solar fuel is a team effort
Daniel Nocera and his team at Harvard are not alone in the search for a viable solution to finding an efficient and commercially sustainable solar fuel. To date, it has taken research in a number of laboratories around the country and for that matter, the world to get to where we are today.
For example, it was another DOE program, called the electrofuels program, that developed the genetically engineered R. eutropha. “The idea was, could you take a bug like Ralstonia eutropha and mess around with its guts, do a bunch of genetic engineering so that bug will take hydrogen, carbon dioxide and make liquid fuel,” said Eric J. Toone, who founded the electrofuels program but is now the director of the Duke Innovation and Entrepreneurship Initiative.
Panasonic, based in Japan has been working on artificial photosynthesis for a number of years. The company’s website focuses on their interest and involvement in the environment as well as their search for a cleaner and sustainable solar fuel. To view Panasonic’s video on artificial photosynthesis, go HERE.
As with many ideas and theories, there are those against the use of artificial photosynthesis and the creation of solar fuels. Stephen Mayfield is the director of the California Center for Algae Biotechnology. In his opinion, the whole solar fuel thing is a “solution looking for a problem.” He goes on to downplay Nocera’s findings, pointing out that solving the problem of turning electrons into biomass has already been done and with using the same bacteria.
“Our problem is not that we have too much H2 and O2 sitting around generated by PV cells that we need to convert it to liquid fuels. Our problem is that fossil fuels were cheap so we burned a boatload of them and now we have problems with our climate,” says Mayfield. He also questions if the process is even carbon neutral, citing the infrastructure needed to run everything, including feeding the bacteria. He just can’t wrap his mind around it, saying, “It’s not that I don’t believe. It’s that damn math thing. It just never works out.”
Nocera agrees that a certain amount of infrastructure is needed, but he goes on to say, “If we used his argument, we would stop working on renewables. You have to build things and that takes carbon. It takes carbon to build silicon but people have shown that the payback is a few years in terms of it becoming carbon neutral.”
