A new leaf: Solar power for the masses

It might sound like the stuff of high school science class, but when researchers and scientists from around the world gather on Lord Howe Island this week to talk photosynthesis, they'll be doing so with a view to solving the current and future energy supply problems of the world.

In high school science terms, we understand photosynthesis to be the process by which plants, some bacteria, and some protistans use the 'unusable' energy from the sun to produce a 'usable' chemical energy. But in terms of energy generation, finding a way to replicate this natural electrochemical process is the holy grail. And when you think of a leaf as "a solar collector crammed full of photosynthetic cells," you begin to understand why.

The quest to create an 'artificial leaf' – or artificial photosynthesis – has been going on for decades.The main aim of the game is to find catalysts that, as The Economist puts it, "can mimic the intricate dance of electron transfers that chlorophyll makes possible." Find this, and you find a way to split water into hydrogen and oxygen gases, that could then be recombined in a fuel cell to create cheap, abundant carbon-free electricity.

And to this end, there have been some promising breakthroughs. In 2009, researchers with the US Department of Energy's Berkeley Lab made the discovery that nano-sized crystals of cobalt oxide could effectively carry out the critical photosynthetic reaction of splitting water molecules.

“Photooxidation of water molecules into oxygen, electrons and protons (hydrogen ions) is one of the two essential half reactions of an artificial photosynthesis system – it provides the electrons needed to reduce carbon dioxide to a fuel,” said Heinz Frei, a chemist with Berkeley Lab’s Physical Biosciences Division, who conducted the research along with postdoctoral fellow Feng Jiao. “Effective photo-oxidation requires a catalyst that is both efficient in its use of  solar photons and fast enough to keep up with solar flux in order to avoid wasting those photons. Clusters of cobalt oxide nanocrystals are sufficiently efficient and fast, and are also robust (last a long time) and abundant. They perfectly fit the bill.”

And this year, MIT chemist Daniel Nocera and his team created much excitement when they unveiled their version of an 'artificial leaf' – a cobalt- and phosphate-coated silicon device the size of a playing card that, when stuck in a jar of water, generated power at an efficiency greater than today's solar panels. And while it's not the first of it's kind (Nocera told Nature.com that John Turner of the US National Renewable Energy Laboratory produced a version back in 1998, but using "really expensive materials... like NASA would use") it is the first to use abundant, cheap materials. "The word here is practical," Nocera says – it doesn't even require clean water to work.

The reality, however, is that Nocera's technology is still a few years from commercialisation. It's “still a science project,” he told MIT News recently. “We haven’t even gotten to what I would call an engineering design.” What's missing from the puzzle, he says, is "some tricky engineering to collect the gases as they're coming off the silicon. We don't know how to do that yet."

But there are plenty of people working to find out. At the time of Nocera's breakthrough this year, four research teams from the UK and US were awarded $10.3 million in funding to overcome limitations in photosynthesis, says NewScientist. In the meantime, Nocera's leaf is being developed as a way to produce power using fuel cells, fed by conventional solar panels. "By the end of 2011, we're going to have prototypes of that on the ground, probably in India," Nocera told Nature.

Still, the ultimate goal is for Nocera's newly-formed company, Sun Catalytix – now in collaboration with global giant Tata Group – to turn the "science project" into a low-cost device that could be used wherever electricity is unavailable or unreliable. As described by MIT News, "it would consist of a glass container full of water, with a solar cell with the catalysts on its two sides attached to a divider separating the container into two sections. When exposed to the sun, the electrified catalysts would produce two streams of bubbles – hydrogen on one side, oxygen on the other – which could be collected in two tanks, and later recombined through a fuel cell or other device to generate electricity when needed."

According to Fast Company, Tata and Nocera envisage the research leading to a refrigerator-sized "mini power plant," that could bring power to the estimated three billion people who are currently living without it.

And that's what this quest is really all about, says Nocera. "The real goal here," he says, "is giving energy to the poor," especially those communities in the rural outposts of countries like Africa, India, and China.

But to Thomas Faunce – Associate Professer at ANU's College of Law and the organiser of this week's conference – the goal is even more fundamental: it's about finding the key to humanity’s future survival.

"Artificial photosynthesis, with timely and coordinated government, academic, corporate encouragement, may become a global phenomenon, deriving inexpensive, local (household and community) generation of fuels and basic foods from simple raw materials – sunlight, water and carbon dioxide – just like plants do," Professor Faunce said in June during a kenote address at the fifth annual Michael Kirby lecture series at Southern Cross University.

"But by using nanotechnology humans can do it better and more efficiently.

"A global artificial photosynthesis project (GAP) could advance existing justice equity and respect for human dignity principles, as well as emerging principles and virtues such as environment sustainability, plus related bioethical principles, health law and international human rights.

"In other words, this is one area where we need to have law and science working side by side if it's going to work."

And that's the idea behind the Towards Global Artificial Photosynthesis conference: to pool the intelligence of international experts in energy policy and governance, energy capture and storage, energy conversion and modified and synthetic biological processes, towards one end: to deal with the needs of an ever-increasing population which, as Faunce puts it, "is rampaging through the environment and destroying it in a never-ending quest for energy."

To address this problem, Faunce says, we must approach it "in a way that fulfills basic social virtues and concepts, like justice and equity, which will have to be complemented by emerging fundamental social virtues, like environmental sustainability reflected in law for these changes to take place."

"GAP [Global Artificial Photosynthesis] is the moral culmination of nanotechnology. It's the reason why we are doing nanotechnology. It also fulfills the foundational social virtue of environment sustainability," Faunce said at SCU.

"It's promoting a community-orientated rather than a corporate-orientated world. There's a hopeful vision about it. And it's satisfying key bioethical and international human rights goals related to the United Nations Millennium Development Goals, as well as core components of a right to health, that is, shelter, food and water. And, in a sense, it satisfies our conscience."

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