Climate News Network

Bionic leaf can fuel energy revolution

June 10, 2016, by Tim Radford

Natural exploitation of sunlight by maple leaves is only a tenth as effective as the new artificial variety. Image: Martin LaBar via Flickr

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Renewable energy experts and microbiologists have teamed up to create a super-efficient artificial leaf that uses photosynthesis to produce carbon-neutral liquid fuels.

LONDON, 10 June, 2016 − Scientists in the US claim to have beaten nature at its own game. They have created a “bionic leaf” that exploits sunlight to create biomass − and they say their invention is now 10 times more effective than an oak or maple leaf.

Two separate laboratories at Harvard University have co-operated to devise, enhance and test a system that uses sunlight to split water molecules and feed the hydrogen to bacteria that then produce liquid fuels. The next task is to scale up the experiment to produce carbon neutral fuels to combat climate change.

“This is a true artificial photosynthesis system,” says Daniel Nocera, a leading researcher in renewable energy who is professor of energy at Harvard. “Before, people were using photosynthesis for water-splitting, but this is a true A-to-Z system, and we’ve gone well over the efficiency of photosynthesis in nature.”

Photosynthesis was perfected by the plant world over more than 3 billion years of evolution. It drives the entire living world and it is the primary source of all fossil fuels.

Ancient sunshine

Climate change became a problem only when humans started to extract ancient sunshine in the form of coal, oil and natural gas, stored in the Carboniferous rocks, and put it back in the atmosphere.

Just as wood fires from felled timber make no difference to the atmosphere’s carbon dioxide levels – because the same forest that shelters the fallen tree will absorb it again – so biofuels converted from surplus maize or sugarcane should, in theory, make no difference to global warming.

So the idea of what the Harvard team call “bionic leaf 2.0” is an attractive one. It could deliver liquid fuels in convenient form that would make no difference to the planet’s overall carbon budget. In effect, it could bypass the vegetation stage.

“It’s an important discovery. It says we can
do better than photosynthesis”

Chemists and engineers the world over are racing to exploit human ingenuity and deliver brilliant solutions, including artificial leaves that can capture carbon dioxide. The challenge is to do so effectively, cheaply and on a massive scale.

Which is why Professor Nocera’s lab teamed up with microbiologists led by biochemist and systems biologist Pamela Silver, of Harvard Medical School.

The scientists report in Science journal that they have devised a hybrid system based on cobalt-phosphorus alloy catalyst partnered with bacteria called Ralstonia eutropha, which splits water into oxygen and hydrogen at low voltages.

Organic chemistry

The microbes consume the free hydrogen and, in the presence of oxygen and carbon dioxide, begin some organic chemistry. So far, the system has made isobutanol and isopentanol, and even a bio-plastic precursor product.

The Harvard scientists say their bionic leaf converts solar energy to biomass with an efficiency of 10%. The fastest-growing plants do the same with an efficiency of 1%.

What works in a laboratory may be tricky to translate into large-scale production, but the researchers are confident they have something that works.

Professor Nocera says: “It’s an important discovery. It says we can do better than photosynthesis. But I also want to bring this technology to the developing world as well.

“If you think about it, photosynthesis is amazing. It takes sunlight, water and air – and then look at a tree. That’s exactly what we did, but we can do it significantly better, because we turn all that energy into a fuel.” – Climate News Network

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  • Wait- what? “Just as wood fires from felled timber make no difference to the atmosphere’s carbon dioxide levels – because the same forest that shelters the fallen tree will absorb it again .” This is an absurd claim. It would perhaps be true *over time* if the net amount of forest was retained, but a recently published paper, “Mapping Tree Density at a Global Scale,” (Crowther et al. , Nature 2015) presents evidence that the earth has lost approximately 46% of its forest cover since the start of human civilization. Where do you suppose all the carbon contained in those trees went? While the FAO has claimed that the rate of deforestation is declining globally, their methodology has not been uniformly accepted; more to the point, there is no dispute that net forest loss continues. To imply, as the author does, that we need not be concerned about the climate impact of cutting and burning trees (never mind the ecological damage caused by deforestation) is to deny a very real and very significant driver of climate change.

  • As our planet is not in thermal equilibrium, carbon neutral does not actually mitigate climate change though it may slow change down a bit. We not only have to cease burning fossil fuels ASAP but also reduce the carbon in the atmosphere starting yesterday, else warming, sea-level rise, ocean acidification etc. will continue to increase for a good while yet with awful consequences. Still this is good news. The obvious application is aviation fuel. However, I would like your leaf to go one better, and actually generate carbon products that can be sequestered, in the restoration of soils for instance, rather than burnt again. Could your leaf become a household roof – supplying power and removing carbon?

  • The idea of carbon neutrality ignores Newton’s Second Law.

    We must somehow get it through our punkin heads that there is no free lunch, that if we want to keep Earth habitable, we must stop using combustion for energy, and sharply reduce our consumption across the board. The most humane way to do the latter is to enforce a one-child policy by post-partum sterilisation of both parents (which the Mainland Chinese never did, whence their constantly growing population). If we do that, AND work our butts off for the next 100 years to make sure that everyone alive gets to live our their lives in peace and dignity, we may be able to thwart the climate collapse and prevent further extinctions, including our own.

    As the late theoretical physicist and systems expert W. Edwards Deming summarised the situation: “It is not necessary to change. Survival is not mandatory”.

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