September 12, 2010 | David F. Coppedge

World’s Top Chemists Can’t Match a Plant

There’s a race on: a race to get cheap energy from the sun.  “The design and improvement of solar cells is one of the most vibrant areas of science,” said the BBC News, “in part because sunlight is far and away the planet’s most abundant renewable energy source.”  Two recent articles show that top labs around the world have not been able to do what plants do with such seeming ease under the sun.
    The BBC News article explores one approach: harvesting real photosynthetic enzymes from plants and employing them on a scaffold of carbon nanotubes.  Michael Strano of MIT and his team have succeeded in getting the enzymes, lipids and surfactants to self-assemble on nanotubes, a promising step that may allow for solar cells that both harvest light and can repair themselves.  Oxygen, unfortunately, is very damaging to solar cells.  “There’s a kind of a horse race among scientists around the world to make the highest efficiency cell, but very few people are asking what happens with that cell when you plug it in for a few hours or for a week or for months.”  Obviously a short-lived efficient cell is no good.  Despite Strano’s advances in mimicking self-repairing structures, “the efficiency of the cells as designed is just a tiny fraction of that provided by the current best solar cells,” the article noted.  Still, plants give him hope that a solution will be found: “What our paper is good for is starting to think about device lifetime and borrowing concepts from nature.  Can we make cells that have an infinite lifetime?”
    A different approach is to imitate what photosynthetic cells do using synthetic materials.  New Scientist reported that chemist Daniel Gamelin at the University of Washington is building on a previous synthetic water-splitting discovery to find ways to mass produce tiny arrays of them, get the cost down and the efficiency up while improving device lifetime.  Meanwhile, a team led by another scientist, coincidentally named Dr. Sun, is at work in Stockholm, Sweden experimenting with different kinds of electrodes that produce more-desirable hydrogen gas instead of hydrogen ions.  Unfortunately, “the efficiency is abysmal” for these and all other electrodes tested so far, said rival John Turner in Colorado at the National Renewable Energy Laboratory.  Dr. Sun would be happy to get 10% efficiency – far below the near-100% efficiency plants get from the sun. Turner has achieved 12% efficiency, but his electrodes are only stable for a few days.  (The best solar cells achieve 27% efficiency.)
    Getting efficiency, durability and low cost in one device is, so far, out of reach.  That’s why the photo in the New Scientist article of green leaves under the bright sun, with its caption “Catching up with nature’s innovation,” remains tantalizing but frustrating.  “Take sunlight, add water, and there you have it: free energy,” the article teased.  “Plants have been doing this for quite some time, splitting water’s hydrogen apart from its oxygen, but our efforts to turn water into a source of free hydrogen fuel by mimicking them have borne no fruit.

Even if their efforts do bear fruit some day, the next trick – bearing fruit, with its seed in itself, after its kind – would make electrolysis look like a fruitcake.  Stories like these are important to remind ourselves that the wonders in nature are far more marvelous than we realize.  If imitation is the sincerest form of flattery, cheap imitation that falls far short of the goal only accentuates the perfection of the original, like a bunch of sports fans with vuvuzelas trying to play a Mozart symphony.
    Plants (even the measliest weeds in your yard) are light-years ahead of human science.  They split water with ease, at near 100% efficiency in ambient temperatures (09/16/2004, 02/10/2010, bullet 1, 05/09/2007), with self-repair (06/29/2010), self-defense (09/13/2006), sunscreen (08/22/2002, 06/23/2006), and automatic response to vastly different light levels and temperatures (01/24/2005, 11/28/2007, 10/13/2008, 05/13/2008).  On top of all that, they then package their technologies in tiny seeds launched into the air or soil or water (06/16/2009, 06/02/2009, 05/11/2007), where they can take root and grow into copies of themselves.  Until you can mimic that, scientists, don’t tell us plants evolved by blind, unguided processes (01/17/2010, 03/23/2009).  Even if you ever succeed (03/27/2010, bullet 2, 01/12/2010, bullet 3), you will have only illustrated the necessity of intelligent design to account for the exquisite engineering we observe in living things.

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