The description above is a gross oversimplification, of course, but in essence this is what a joint paper published in the journal Science [03 May 2011, paywalled, Comparing Photosynthetic and Photovoltaic Efficiencies and Recognizing the Potential for Improvement] is saying. The target for this improvement on nature is biofuels.

The study itself compares the efficiencies of solar photovoltaic devices (solar panels, etc.) compared to photosynthesis and finds photosynthesis lacking. For evolutionary reasons, most photosynthesis occurs with the green and some blue portions of the spectrum. This is sufficient for the needs of plants and algae. It is not, however, good enough for human energy needs.

The solution, as these scientists propose, is to create hybrid organics (plants, algae) that can absorb photons (solar energy) in different colors and install them in tandem so that more of the Sun’s energy is captured simultaneously. Prototypes of this approach are already underway, but the techniques are difficult, essentially the building of plant material from scratch using synthetic biology and genetic manipulation. The results may be startling, with much darker plant colors and plant forms that may seem alien.

Keep in mind this paper is a proposal, an outline, of an approach that will involve a lot of new research. That means it will take years before tangible results are available. On the other hand, human beings have been modifying plant life for millennia. This is an accelerated process of modification. The fact that we may be building new plant life from scratch with basic organic building blocks may seem radical, and it is, but it’s hardly shocking. Presumably researchers will deal with ecological impact and other environmental issues if and when these synthetic plants are real and viable.

The “leaf” in this case is a silicon-based square about the size of a large business card. Drop it into water with plenty of direct sunlight and its catalytic properties split the molecules of water (H20) into hydrogen and oxygen gas. Anyone who follows alternative energy will immediately recognize what this means – fuel cell. The hydrogen gas is the primary source of energy for fuel cells, one of the big hopes for the future of clean “green” energy.

Unfortunately, color me skeptical, not green.

There are labs all over the world working on various forms of artificial photosynthesis. This particular artificial leaf idea comes with good pedigree from the lab of Daniel Nocera at the Massachusetts Institute of Technology (USA). He got the idea from researchers at the U.S. National Renewable Energy Laboratory (Boulder, Colorado), who developed a similar device in 1998 but used platinum, or other similarly expensive materials for catalysts and which did not last a day. The achievement for the MIT lab was to use much less expensive materials, nickel and cobalt, to operate continuously and at a high level of output for around 45 hours. The key is that this ‘artificial leaf’ produces gasses that can be stored and used in a fuel cell system – there is no need for electrical storage such as a battery.

This sounds great and the researchers are not bashful about it:

“A practical artificial leaf has been one of the Holy Grails of science for decades. We believe we have done it. The artificial leaf shows particular promise as an inexpensive source of electricity for homes of the poor in developing countries. Our goal is to make each home its own power station.”

[Source: EurekAlert]

The claim is that the ‘leaf’ could provide up to 30 kilowatt-hours of electricity per day, roughly equivalent to the electrical use of an American household.

This would indeed be quite wonderful, revolutionary, in fact. I wish, however, that the accompanying press release and most of the coverage this has received would also emphasize that:

- This is a presentation of a concept (at the American Chemical Society convention), with a prototype catalytic device.
- The findings for the newest device are not yet published in a peer reviewed journal.
- This is not a working device in the sense that it hasn’t been paired with a functional fuel cell environment.
- A production-ready fuel cell based on this technology is years away (actually, the researchers do mention this).
- One of the known hurdles for all such technology is the ability to ‘scale,’ that is, can it be manufactured in large quantities?
- Like traditional solar cells, this device requires direct sunlight – what are the specific necessary operating conditions for long-term high output?

There are always questions about technology that supposedly has a major impact. Not addressing them squarely leads to skepticism. It’s a standing notion in science that extraordinary discoveries require extraordinary evidence. That level of detail and planning has not accompanied this announcement of technology.

Note these are reservations that should apply to any significant technology at this early stage of its development. In defense of Dr. Nocera and the researchers at MIT – who do have a good idea of science and technology requirements – the ‘artificial leaf’ has been in the works for several years, and practicality has always been the focus. It is also true that Dr. Nocera and MIT inked an agreement in October of 2010 with the Tata Group of India (the company that developed the world’s least expensive car) for further development of the concept. So somebody (big) is putting money where their mouth is. All to the good. The world sorely needs inexpensive, small-scale, minimal polluting sources of energy.

With this kind of motivation and for the most part adequate money, scientists and their engineering brethren are hard at work on scientific and technological fixes for the looming energy crisis. The work takes many paths, not all of which lead anywhere, but they don’t know that until they try them.

That said; here are two relatively ‘out there’ stories of work in progress on solar energy. They both take their cue from plant life. One is about creating an ‘artificial leaf’ to produce electricity, the other is about solar cells that regenerate – just as leaves do when sunlight breaks down the chemistry of photosynthesis.

Water-gel solar device like a synthetic leaf

The concept is not hard to describe: Take a water-based gel, mix in some light-sensitive molecules, add electrodes coated with carbon nanotubes. When the light-sensitive molecules become excited (electrically charged) by sunlight, the electrodes tap the charge for use elsewhere. Something like this happens when plants capture sunlight for the production of glucose in photosynthesis, which is how studying plant biology inspired the approach.

A team of researchers from the United States and South Korea led by Dr. Orlin Velev from North Carolina State University (Raleigh, USA) have reported their proof of concept for mixing water-based gels (in the jargon, aqueous soft gels) with photosensitive compounds (including chlorophyll) in the Journal of Physical Chemistry Aqueous soft matter based photovoltaic devices. The photovoltaic devices created by the team are made with inexpensive materials and can be flexibly packaged in both a literal and figurative sense. Sounds good, but this is work in the very early stages.

“The next step is to mimic the self-regenerating mechanisms found in plants,” Velev says. “The other challenge is to change the water-based gel and light-sensitive molecules to improve the efficiency of the solar cells.”
…
“We do not want to overpromise at this stage, as the devices are still of relatively low efficiency and there is a long way to go before this can become a practical technology,” Velev says. “However, we believe that the concept of biologically inspired ‘soft’ devices for generating electricity may in the future provide an alternative for the present-day solid-state technologies.”

[Source: North Carolina State University]

Self-regenerating solar cells

We’ve all seen how sunlight can make fabric colors fade. Ever wonder why the color of leaves doesn’t fade? (Discounting, of course, seasonal changes.) Actually, they would fade as the sunlight used for photosynthesis also breaks down the plant’s chemistry, but nature has developed ways for the chemistry to automatically regenerate. Scientists would like to do that too, regenerate as people no doubt, but this is about imitating nature for regenerating solar cells.

Solar cells degrade under the power of the sun. This is especially true for the new organic solar cells. To get around the problem, Michael Strano and a team of colleagues at the Massachusetts Institute of Technology (MIT, Boston, USA) studied how plants regenerated their photosynthesis chemistry. Published in Nature [Photoelectrochemical complexes for solar energy conversion that chemically and autonomously regenerate] the approach they developed is not difficult to describe: A solution is created containing carbon nanotubes, bacterial light-harvesting proteins, tiny discs made from the lipid molecules that form the membrane of cells (phospholipids), and a surfactant. The surfactant, a chemical that makes the molecules of a liquid spread, prevents the mixture from interacting.

Remove the surfactant with a filter and the proteins bind to the lipids, which attach to the nanotubes – all self-assembling. Expose this mixture to sunlight and the light-harvesting proteins generate a charge that is carried to the electrical contacts of the solar cell by the carbon nanotubes. Eventually the proteins break down. Pour in surfactant, the molecules disperse, add some new protein molecules, take out the surfactant again – and the solution regenerates. Repeat as needed for efficiency.

Crude as this is, the team assembled cells that produced electricity for 32 hours and required 8 hours for regeneration. Even including the hours of regeneration, this cycle was at least 300% more efficient than non-regenerative organic solar cells. At the molecular level, this new solar cell is operating at about 40% efficient; roughly double that of the best commercial solar cells. The difficulty will be to continuing this level of efficiency in a device that can survive mass production and commercial competition. There are plenty of practical hurdles, for example, how are the protein molecules to be replenished for the regeneration cycle? How, physically, is the removal and injection of surfactant to be handled?

Theoretically, the efficiency of the structures could be close to 100 percent, Strano says. But in the initial work, the concentration of the structures in the solution was low, so the overall efficiency of the device — the amount of electricity produced for a given surface area — was very low. They are working now to find ways to greatly increase the concentration.

[Source: EurekAlert]

Now a new collaborative team, including Graham Fleming, has added confirmation that the photosynthetic process uses quantum entanglement to utilize nearly 100% of the sun’s energy in the conversion of sunlight to carbon-based (sugar) energy.

The new study published in the journal Nature Physics in May, provides confirmation of quantum effects in a specific photosynthetic mechanism, and according to Mohan Sarovar, one of the authors:

“…this is the first instance in which entanglement has been examined and quantified in a real biological system.”
…
“We present strong evidence for quantum entanglement in noisy non-equilibrium systems at high temperatures by determining the timescales and temperatures for which entanglement is observable in a protein structure that is central to photosynthesis in certain bacteria.”

[Source: Lawrence Berkeley National Laboratory]

Quantum entanglement is one of the signature effects in the strange-seeming world of quantum physics. It basically involves two atomic particles, which though physically separated, behave as if they were one particle; they are ‘entangled.’ The new study establishes that various pigments in a specific light harvesting protein (called, technically, the Fenna-Matthews-Olson or FMO protein) use quantum entanglement to simultaneously choose the optimum pathway for capturing photons of light – capturing all of them. Such efficiency human engineers can only dream about.

Having demonstrated entanglement in the FMO protein, the researchers believe the same effect will also be found in larger light harvesting proteins and, in fact, there may be multiple instances of the effect to act like a kind of highly adaptive filter, trapping the photons of light as they penetrate into the pigments of the protein.

The researchers remain surprised at much of what they discovered: That the entanglement effect persisted even when the molecules of the protein were not strongly coupled (connected) with electronic and vibrational states, and that temperature has so little impact on the process. It appears that the light harvesting quantum effects in plants are almost immune to heat – especially in comparison to quantum effects that are produced in the laboratory.

It should be emphasized that this is pioneer work. Only a few years ago, most scientists did not consider the possibility that natural processes might use quantum effects. Now we are nearly sure that quantum effects lie at the heart of one of the most important natural processes of all. Photosynthesis is the basis of most life as we know it (including our own, since we must eat energy produced by photosynthesis). Eventually, some of the knowledge gained in this area will contribute to human-made artificial photosynthesis. It may also be a path that leads to other fundamental discoveries about the nature of quantum physics, which are now almost totally unsuspected. Great stuff for both biologists and physicists.

The development of a ‘natural’ (biological) and efficient way to split water is potentially very important. Of course, there are many uses for deriving hydrogen from water – fuel cells, hydrogen cars, for example. This particular approach, developed by a team led by Angela Belcher (Massachusetts Institute of Technology, USA), professor of materials science, uses a common bacterial virus (a virus that infects only bacteria) as the structure (or scaffolding) to hold the photosynthetic components. The virus was genetically engineered to bind to the two components: zinc porfyrins, a kind of organic pigment (like the red in red blood cells), which was used as the photoreceptor; and iridium oxide, which was the catalyst for the conversion.

The treated viruses became, in effect, wires. They became wires that absorb photons from light for energy and hold the catalyst for the chemical reaction with water. Most other approaches to photosynthesis have tried to use the organic (plant) material, usually resulting in dead plant material. Dr. Belcher reasoned that it might work better to use the organic matter as a scaffold to hold the artificial components in place. Better still, the virus proves to be an active organizer of the photosynthetic process, making it more efficient.

There is a problem though, right now the photosynthetic process produces oxygen and also splits the hydrogen into its fundamental protons and electrons. Now the researchers have to come up with a way to put the protons and electrons back together as hydrogen. This is what I meant by a technology not fully implemented. They’re also trying to find a catalyst that is less expensive than iridium oxide. The prognosis might be even gloomier. Take the words of Thomas Mallouk, the DuPont Professor of Materials Chemistry and Physics at Pennsylvania State University, who was not involved in this work…

“This is an extremely clever piece of work that addresses one of the most difficult problems in artificial photosynthesis, namely, the nanoscale organization of the components in order to control electron transfer rates.”

He adds: “There is a daunting combination of problems to be solved before this or any other artificial photosynthetic system could actually be useful for energy conversion.” To be cost-competitive with other approaches to solar power, he says, the system would need to be at least 10 times more efficient than natural photosynthesis, be able to repeat the reaction a billion times, and use less expensive materials. “This is unlikely to happen in the near future,” he says. “Nevertheless, the design idea illustrated in this paper could ultimately help with an important piece of the puzzle.”

[Source: EurekAlert]

I was particularly struck by the phrase “…need to be at least 10 times more efficient than natural photosynthesis…,” which will be difficult because photosynthesis is about 3-6% efficient. Hitting 60% efficiency will be…difficult; 30% perhaps not so much. In any case, the researchers are aware that this is just the beginning of the road to artificial photosynthesis and/or conversion of water to oxygen and hydrogen by natural means. Whatever the ultimate practical value, the point is still made: This kind of work opens eyes, provides new methods, and perhaps will provide insights that are useful for other, better, approaches.

We can think about this in terms of Feynman’s way of talking about quantum mechanics: rather than a particle taking a unique path between two points, as in classical mechanics, a quantum particle takes every possible path, with simple paths getting a bit more weight than complicated ones. In the case of the protein, different paths for the energy might be more or less efficient at any particular moment, but this bit of quantum trickery allows the energy to find the best possible route at any one time. Imagine at rush hour, if your car could take every possible route from your home to the office, and the time it officially took would be whatever turned out to be the shortest path. How awesome would that be?

[Source: Quantum Photosynthesis; Cosmic Variance]

The pioneering work, done by a team of chemists at the University of Toronto (Canada), started with collecting what are called ‘light-harvesting complexes’ from two species of marine algae. Light-harvesting complexes capture photons from sunlight and use them to excite electrons in protein compounds to higher levels – a transfer of energy. Later that energy can be attached to organic compounds, such as glucose (sugars), for storage. These light-harvesting complexes were stimulated with femtosecond pulses of laser energy to simulate sunlight, and observed with a two-dimensional electronic spectroscope. What they found was that during this conversion the same quanta of energy existed in two places at once (in the photon and in the electrons) – a quantum superposition – which is a hallmark characteristic of quantum mechanics.

This was a surprising and highly suggestive result. As one of the researchers put it:

“There’s been a lot of excitement and speculation that nature may be using quantum mechanical practices,” says chemistry professor Greg Scholes, lead author of a new study published this week in Nature. “Our latest experiments show that normally functioning biological systems have the capacity to use quantum mechanics in order to optimize a process as essential to their survival as photosynthesis.”

“This and other recent discoveries have captured the attention of researchers for several reasons,” says Scholes. “First, it means that quantum mechanical probability laws can prevail over the classical laws of kinetics in this complex biological system, even at normal temperatures. The energy can thereby flow efficiently by—counter intuitively—traversing several alternative paths through the antenna proteins simultaneously. It also raises some other potentially fascinating questions, such as, have these organisms developed quantum-mechanical strategies for light-harvesting to gain an evolutionary advantage? It suggests that algae knew about quantum mechanics nearly two billion years before humans,” says Scholes.

[Source: EurekAlert]

The finding also suggests that if this quantum-based process is correctly identified, that other biological processes may also utilize quantum mechanics in ways that, up to now, science has not even considered. Oh my, goodness.