The years-long quest to make an ‘artificial leaf’ as a promising fuel alternative

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More than 10 years ago, Miguel Modestino was a PhD student at the University of California Berkeley and he worked on a research project that had the promise of turning solar energy into fuel. 

It would replicate what leaves do: use solar energy to break water into hydrogen and oxygen, and add carbon dioxide to produce a source of fuel. Leaves make sugar, a “fuel” that helps plants grow. The artificial leaf would make fuel that can be used to generate electricity. 

“The concept of an artificial leaf is beautiful. It’s inspiring. It’s one of the reasons why I first joined my research group,” said Modestino, who is now an associate professor of chemical engineering at New York University. “Engineering is not always pretty and inspiring, but it’s focused on getting something done and getting something done as efficiently and as good as you can.” 

In the years since, Modestino and the other researchers have run into obstacles, particularly with making their devices profitable, but they continue to work on the research. The question is whether this technology could improve and become widespread quickly enough to help counter the effects of climate change. 

“You start with a vision and idea, and those ideas take shape and forms that you really never predicted,” Modestino said. 

The main hurdle is that existing sources of power like fossil fuels are cheap, making it hard for hydrogen or other fuels from an artificial leaf to compete. 

“Clean fuels do the same function as dirty fuels,” he said. “You need to compete on very similar markets, and fuel markets are hyper competitive.” 

He cast around for something he could make with an artificial leaf that would have a smaller environmental footprint compared to an existing product, and also compete when it comes to price. He landed on nylon, because it’s a valuable chemical that is popular in clothing for products like swimsuits or active wear. Companies now make nylon from crude oil; Modestino’s goal is to use the artificial leaf technology to make nylon and other chemicals using solar power and materials that can be grown. 

“There have been tremendous developments, some of them pushing the artificial leaf concept forward and some of them branching out in directions that are different but leading to advances in many other different fields,” Modestino said, adding that the final goal is “abundant, inexpensive, renewable energy deployed everywhere across society.”

Chemist Dan Nocera inspired Modestino’s work by popularizing the concept of an artificial leaf. Nocera has also hit the same challenges Modestino encounters, and is now a professor of energy at Harvard University. He spun off his research into a separate company, which started making large scale batteries. The defense contractor Lockheed Martin bought that company in 2014. Two years ago, the Army base in Fort Carson, Colorado, started building one of these batteries, which could power hundreds of homes. 

Nocera looked for other ways to adapt the artificial leaf research, and decided to apply it to making fertilizer, which also has a large carbon footprint. He started with genetically engineering bacteria to “be like a hibernating bear: take the hydrogen from water, solar water splitting, take carbon dioxide, and make this energy rich biopolymer and store it.” 

He said the bacteria consumes a lot of hydrogen and carbon dioxide like a bear preparing for winter to “become sort of obese on energy … you can look at the bacteria and they get all puffed up.”

The puffed up bacteria then goes into the ground, where it decomposes to become fertilizer. He founded another company based on this work, which he said now makes and sells fertilizer at the same cost of commercial fertilizer made from mined chemicals or natural gas.

These developments are promising to physicist Varun Sivarum, a senior fellow for energy and climate at the Council on Foreign Relations. In his 2018 book, “Taming the Sun,” he surveyed solar energy projects around the world, and said he is now “delighted” at how the cost of solar energy has gone down to “below 10 cents a watt for a solar panel, a level I thought unthinkable just about a decade ago.” 

However, his concern is that the artificial leaf research is not progressing fast enough to tackle climate change. He said the clean energy sector has a joke about how for decades now, people have said nuclear fusion is just 10 years away. 

“The artificial leaf, I hope, does not fall into this trap because the artificial leaf has had a great deal of promise … for multiple decades now,” he said. “If you ask me today, it still feels like we’re a decade away from these technologies being truly commercially competitive, if not longer. I don’t think we can afford that.”

He pointed out that since the modern solar panel was invented around 70 years ago, solar energy is “literally taking over the world,” but humans cannot afford to wait another 70 years for research from artificial leaf projects to catch up with fossil fuel based chemical production. 

Chemist Dan Nocera agrees, but said that is out of the hands of scientists like himself. 

“You invent and create and it gives people in society more options. But once I’ve done that as a scientist, it’s out of my control if they choose that option or not,” he said. “Since the 1900s as a society, we’ve invested hundreds of trillions of dollars into an energy infrastructure. There is no scientist who’s going to come up with something in their lab tonight that replaces a hundred trillion dollar paid off energy infrastructure.”