Chemists Create ‘Artificial Photosynthesis’ System Ten Times More Efficient Than Existing Systems

For the past two centuries, humans have relied on fossil fuels for concentrated energy; hundreds of millions of years of photosynthesis packed into a convenient, energy-dense substance. But this supply is limited and the consumption of fossil fuels has a considerable negative impact on the Earth’s climate.

“The biggest challenge that many people don’t realize is that even nature has no solution for the amount of energy we use,” said University of Chicago chemist Wenbin Lin. Even photosynthesis isn’t as good, he said: “We’ll have to do better than nature, and that’s scary.”

One possible option scientists are exploring is “artificial photosynthesis” – reworking a plant’s system to make our own kinds of fuels. However, single-sheet chemical equipment is incredibly complex and not so easy to use for our own purposes.

A Natural catalysis A study by six University of Chicago chemists shows an innovative new artificial photosynthesis system that is an order of magnitude more productive than previous artificial systems. Unlike ordinary photosynthesis, which produces carbohydrates from carbon dioxide and water, artificial photosynthesis could produce ethanol, methane or other fuels.

Although it still has a long way to go before it becomes a way for you to power your car every day, the method gives scientists a new direction to explore and may be useful in the short term for the production of other chemical products.

“This is a huge improvement over existing systems, but just as importantly, we were able to exhibit a very clear understanding of how this artificial system works at the molecular level, something that has never been accomplished before,” said Lin, who is the James Franck Professor of Chemistry at the University of Chicago and lead author of the study.

“We will need something else”

“Without natural photosynthesis, we wouldn’t be here. It created the oxygen we breathe on Earth, and it makes the food we eat,” Lin said. “But it will never be efficient enough to provide us with fuel to drive cars, so we will need something else.”

The problem is that photosynthesis is designed to create carbohydrates, which are great for fueling us, but not for our cars, which need much more concentrated energy. Researchers looking to create alternatives to fossil fuels therefore need to rethink the process to create more energy-dense fuels, such as ethanol or methane.

In nature, photosynthesis is carried out by several very complex assemblies of proteins and pigments. They absorb water and carbon dioxide, pull molecules apart, and rearrange atoms to form carbohydrates, a long chain of hydrogen-oxygen-carbon compounds. Scientists, however, need to rework the reactions to instead produce a different arrangement with just hydrogen surrounding a juicy carbon core – CH₄also known as methane.

This reengineering is much trickier than it looks; people have been tinkering with it for decades, trying to get closer to nature’s efficiency.

Lin and his lab team thought they might try adding something that artificial photosynthesis systems haven’t included to date: amino acids.

The team started with a type of material called a metallic organoframework, or MOF, a class of compounds made up of metal ions held together by organic binding molecules. Then they designed the MOFs as a single layer, to provide the maximum surface area for chemical reactions, and immersed everything in a solution that included a cobalt compound to transport electrons. Finally, they added amino acids to the MOFs and experimented to see which worked best.

They were able to make improvements to both halves of the reaction: the process that separates water and the one that adds electrons and protons to carbon dioxide. In both cases, the amino acids helped the reaction to proceed more efficiently.

However, even with vastly improved performance, artificial photosynthesis still has a long way to go before it can produce enough fuel to be relevant for widespread use. “Where we are now, it would have to increase by several orders of magnitude to produce enough methane for our consumption,” Lin said.

The breakthrough could also be widely applied to other chemical reactions; a lot of fuel has to be produced for this to have an impact, but much smaller amounts of certain molecules, such as the raw materials to make pharmaceutical drugs and nylons, among others, could be very useful.

“A lot of these fundamental processes are the same,” Lin said. “If you develop the right chemistries, they can be connected to many systems.”