Bionic leaf might power Earth
Using artificial and bionic leafs, a Harvard scientist with New Zealand links has created solar biofuels that could run engines. Veronika Meduna reports.
"I can use sunlight and water to power the Earth."
It's a bold statement, but Harvard University chemist Daniel Nocera is more than delivering on its promise with a string of potentially game-changing technologies.
His trick is to learn from nature, and in particular from plants, which are rather good at using sunlight and water to generate energy. Nocera set himself the challenge of mimicking the process of photosynthesis – and he is now producing solar biofuels even more efficiently than plants.
As a member of the MacDiarmid Institute's International Science Advisory Board, Nocera shares his knowledge with New Zealand scientists working on solar energy and new materials aimed at making solar panels cheaper and more versatile.
The fossil fuels we rely on today once started out as sunlight, providing the energy plants need to combine water and carbon dioxide into sugars that fuel their growth. The first step in natural photosynthesis is the splitting of water into oxygen and hydrogen, and in 2011, Nocera developed an artificial leaf which does just that, as well as or even better than plants.
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The artificial leaf is smaller than a playing card and as thin as a real leaf. At its core is a wafer of silicon, the material used in standard solar panels. It is sandwiched between two coats of chemical catalysts. The silicon's job is to absorb sunlight and to pass the energy to the catalysts, which then in turn pull water molecules apart. One catalyst produces oxygen, the other makes hydrogen – and in 2011 the artificial leaf was hailed by Time magazine as the innovation of the year for its potential to efficiently distil and store the energy of sunlight as hydrogen fuel.
"What's different from a solar panel is that none of this is wired up. It's just simply coating. When light hits the silicon the charge goes straight into the catalysts, and once they are energised they can split water."
Solar panels on the roof work only when the sun is out, but the artificial leaf technology provides a way of storing the harvested energy, he says. "Once you have the hydrogen you could store it so that even when the sun goes down at night you have this rich fuel, which you could use in your house. You could burn it or, better still, use a fuel cell to make electricity."
Nocera could have stopped there. But hydrogen is a combustible fuel and difficult to transport. He says even though several car makers have developed models that run on hydrogen fuel, they haven't taken off because of the challenges in setting up hydrogen refuelling stations.
So he turned the artificial leaf into a bionic leaf, with help from a microbe and some scientists specialising in synthetic biology. This system mimics the second step in natural photosynthesis. The genetically engineered micro-organisms take the hydrogen fuel generated by the artificial leaf component and uses carbon dioxide to produce liquid biofuels. Scientific American and the World Economic Forum declared the bionic leaf as the breakthrough technology for 2017.
Nocera's bionic leaf has already produced a suite of solar biofuels that you could use to run an engine. The technology seems ideally suited for cheap, small-scale, distributed biofuel production, which works even in dirty or ocean water. So what's stopping it from being commercialised?
"The multi-trillion-dollar infrastructure that the world has invested in," he says. "We've built this huge infrastructure and spent a huge amount of money, so there's nothing any scientist can do to compete or displace 20 or 30 trillion dollars' worth of investment over the last 100 years in a fossil fuel-based infrastructure.
"We argue whether this [renewable energy] is cheaper, but that's a relative term. If I were to go back a 100 years before the world built this infrastructure, then yes, this is way cheaper than the path the world decided to take. To get off that now you should price carbon, put a tax on carbon dioxide, and things will go quicker."
Ultimately, he says, none of the existing methods we use to generate electricity, including nuclear power, have the capacity to meet world energy demands. The same applies to electric vehicles. "Batteries store 50 to 100 times less energy than fuel, and they can't get better. You can't talk about powering the Earth with batteries, they just don't store enough energy, but they are close to an infrastructure where people can make money from it.
"That's fine and I'm all for it but when we start talking about saving the planet, batteries just can't do it and we're going to need [renewable] fuels."
Nocera's focus for now is on emerging economies "where they haven't made that investment yet into a centralised power generation infrastructure, but are making that decision now."
There is an added motivation in this approach. Developing and emerging economies are likely to have the biggest growth in energy demand in coming decades, and Nocera hopes that the bionic leaf, which is already 10 times more efficient than plants in making renewable solar fuels, could take care of this projected increase in energy consumption without adding further greenhouse gas emissions to the atmosphere.
"The projected growth in energy consumption will drive climate change in the future, so it's logical to go there. That's where you're going to have the most carbon in the atmosphere and they don't have this large infrastructure that you have to fight against. My goal is to power at least the growing energy demand with water and sunshine."
Nocera's approach is part of his broader thinking about how science can contribute to society. "How most people do science is that they study something and create new knowledge or a discovery – and they hope that this will someday make it into the world, which it might. But I get to invent things more quickly because I work backwards. I ask what are the big problems in the world, and is there some science that needs to be discovered to solve the problem. If there's some new science to do, I'll do it."
As if his new science so far isn't enough, Nocera's most recent invention, announced earlier this year, has transformed the bionic leaf into a system that makes nitrogen fertiliser. It uses a different engineered microbe that, when added to soil, makes fertiliser on demand – and could disrupt another expensive and energy-hungry industrial process the world embraced more than a century ago.
Daniel Nocera is expected to visit New Zealand next year.