The Nano Revolution 2: Learning from Biosystems
While humans have been experimenting for centuries, nature has been doing it for millions of years. Biological systems are far superior to human creations when it comes to using nature’s gifts like sun’s energy. Biology combined with nano could lead to major breakthroughs.
Second of the series
Column by Dr. N.S. Rajaram, Contributing Editor
Biology: promise and the challenge
Our dream of using the limitless resources of the sun to generate power is getting ever closer to reality. But challenges remain, especially in storing energy. Also, systems and processes we have created so far are quite primitive when compared to what nature has accomplished. This was first brought home to me when my colleagues and I were working on robotics for NASA applications. We found, when it came to strength and efficiency, even the most advanced man-made materials were no match for human and animal muscle. This is even more true of applications involving sensory input like vision and touch. Computer vision systems, now making their way into industrial plants are extraordinarily primitive compared to what human and animal senses are capable of.
In designing systems, we depend mainly on physics and chemistry. Biological systems on the other hand work on biophysical and biochemical principles that are not easy to replicate in the laboratory, much less in the workplace. Plants for example make sugars using energy from the sun employing a process called photosynthesis. Protein chains convert light energy into electrons which drive the plant’s sugar-producing factories. Remarkably, nearly all of the sunlight falling on them gets converted into electrons, meaning they achieve near 100 percent conversion efficiency. This is because these plant proteins, which are the result of millions of years of evolution, are optimized to maximize solar energy use. Nature has done its homework by eliminating inefficient ‘workers’ through natural selection. Only the fittest remain.
Commercial solar panels which are based on the photoelectric phenomenon are nowhere near this efficient. They convert less than 20 percent of the light falling on them. Among other things, currently available photovoltaic cells convert radiation (light) falling within a relatively narrow frequency band. A major area of research is to extend this band to include ultraviolet and thermal (or infrared) frequencies also. In addition, we humans have still not mastered the art of storing energy while plants both generate energy from the sun and also store it.
Researchers hope that nanotechnology may become the link between the physical sciences and the creation of systems that mimic biological systems and their functions. We must recognize, however, that when we do succeed in mimicking biological functions, they will not necessarily function like plants. This is what we learned in creating artificial intelligence programs and robots. Computers don’t think like humans: a chess playing program doesn’t play chess like a chess master thought it may beat him.
Biosynthesis: plant doping
A widely used method for altering the properties of materials is to add impurities. This is called ‘doping’. In fact doping is indispensable in semiconductor manufacturing. (Solar panels are also semiconductor devices.) It has been found that titanium dioxide, particularly in what is called the anatase form, is a photocatalyst under ultraviolet (UV) light. Recently it has been found that titanium dioxide, when spiked with nitrogen ions or doped with metal oxide like tungsten trioxide, is also a photocatalyst under either visible or UV light. This means that with proper doping, it is possible to extend the conversion frequencies to the ultraviolet range.
This may be called conventional doping. But now researchers are using plant molecules (like DNA) to dope materials. At the Massachusetts Institute of Technology, physicist Andreas Mershin and his colleagues say they have simplified the production of plant-based solar cells so that any lab can make them. This new solar panel is green both literally and in spirit. Instead of using semiconducting silicon, proteins from plants transform light into electricity. But this is only a beginning since their cells have a long way to go before becoming practical on a commercial scale.
Mershin’s idea is to reproduce the efficient electron generation process in plants to generate electricity to be used by people. This means building a working solar panel using proteins instead of (or in addition to) photovoltaic materials like silicon. This required proteins on the surface to be stabilized so that they perform just like they do in cells. To do this, Mershin had to attach enough of them to generate a measurable current. And this is where nano comes into the picture. He found he could achieve this by painting the protein solution on a glass slide covered with nano-sized rods of zinc oxide. The rods hold more protein than the flat surfaces commonly used to make photosynthetic solar panels.
In order to achieve all this, Mershin had to extract a type of light-collecting protein chains from photosynthetic bacteria. The picture illustrates the scheme, though not exactly the same as Mershim’s but similar. In the diagram, a strand of DNA (the figure 8 coil) is attached to a bundle of proteins called peptides. The gray cylinders are carbon nanotubes. They are needed to hold in place the corkscrew-shaped peptides which are coated with a special virus. Yellow spheres are titanium dioxide used to coat the molecules (pink spheres) surrounding the bundle.
All told, it is a real tour de force that involves nanotechnology and biology. But we have a long way to go before we begin to see them in the field.
Nano Leaf for the storage challenge
Although remarkable progress has been made in the generation of solar and wind power, several problems need to be solved before its utilization can become widespread. Of these the most challenging is storage. Solar power plants generate dc (direct current) power while we use mostly ac (alternating current) power though it is often converted into dc in many of our appliances. It can be said that while the challenge of ac power is transmission, the main challenge of dc power (like solar) is storage.
To see this we must recognize that solar power generation is intermittent— it is interrupted when there is no sunlight. So we need some other source of power during that time, like in nighttime. Small power users like domestic consumers can use ordinary batteries that can be charged by solar power and used as the source at night. This has limitations and not practical for large consumers like industries. Plants create and also store energy in the form of sugar and other chemicals. One possibility is to try to mimic this by using solar powerto breakdown water into hydrogen and oxygen to be stored and used later to generate clean energy.
Daniel Nocera of MIT (now at Harvard) has created what is being called the ‘artificial leaf’ by borrowing from the process of photosynthesis to split water to produce molecular oxygen and hydrogen, which is a form of separated protons and electrons. The primary steps of natural photosynthesis involve the absorption of sunlight and its conversion into spatially separated electron–hole pairs. (A hole is a positively charged entity created by electron gap.) The holes of this wireless current are captured by the oxygen evolving complex (OEC) of what is called photosystem II to generate oxygen from water by oxidation.
Nocera and his colleagues’ idea is to replicate this phenomenon or something like it in the laboratory and eventually produce an ‘artificial leaf’. For a synthetic material to realize thesolar energy conversion function of the leaf, the light-absorbing material must capture a solar photon (light particle) to generate a wireless current that is harnessed by catalysts. These catalysts in turn drive the four electron/hole fuel-forming water-splitting reaction under suitable conditions and under normal solar illumination falling on a leaf (about 0.1 watt per cm2).
Without going more into technical details, we may say the goal is to construct a simple, stand-alone leaf-like device composed of abundantly available materials. Such an artificial leaf provides a means for an inexpensive and highly distributed solar-to-fuels system that employs low-cost systems engineering and manufacturing. The important thing to note is that when fully practical, Nocera’s invention gives us a way of storing electricity; the source itself can be anything, solar or wind power.
If only we could store energy
It may be that in the long run storage will prove to be both more important and prove a greater challenge than power generation. Strange as it may sound, we have too much energy,but we don’t know how to store it. Many of us have noticed that wind generators are idle much of the time. This is because there is too much power available, and the grid can’t absorb the extra electricity especially since it flows intermittently. (For stability reasons we cannot have more than 10 to 15 percent intermittent load on any grid.) In fact, the world wasted 25 tera watt-hours (a million megawatt hours) of potential electricity generation from windmills last year because we had no way of storing all this excess power. It will be the same when solar power becomes abundant. Storage is the real challenge.
If the goals of Nocera and his colleagues are realized, we will eventually have a device (nano leaf) that not only generates cheap energy from the sun (and/or water) but can also store it. This will be like a computer chip that has both the processor and the memory on it. (Plants already do it.) When this happens, it will be possible to design cars and other vehicles that use water as fuel. This in fact is one of the goals of industry today.
One person who has been impressed by the work of Nocera and his team is the Indian industrialist Ratan Tata. As of a year ago, Tata had put $15 million into Nocera’s research. There are reports that Nocera and Tata will jointly float a start up venture to build a prototype that can store hydrogen in a compressed form and fit it into a car for using as an alternative fuel. As a first step they plan to build a prototype that can hold hydrogen in a compressed form that can fit into a car to be used as an alternative fuel. Nocera holds a patent that may prove to be a key to realizing it.
The company in question could be Sun Catalityx, founded originally by Nocera. Its goal is to produce a power plant about the size of a refrigerator but capable of generating enough electricity to power a small home using only water and sunlight. The artificial leaf system, which will be the key to the power plant, will also have wireless capabilities. This means the home ‘wiring’ will be wireless like a WIFI network. If this comes to pass, each home will have its own power plant and its electrical network. Then it will be “Good bye electrical grids.”
Here again nano is crucial. “Because there are no wires, we are not limited by the size that the light-absorbing material has to be,” says Steven Reece, a research scientist with Nocera’s company who worked on the discovery. “We can operate on the micro- or even nanoscale…so you can imagine micro- or nanoparticles, similar to the cells we’ve worked with here, dispersed in a solution.” How much of this will actually be realized and when remains to be seen. Nonetheless their work so far has been sufficiently convincing for Ratan Tata to pump a cool $15 million into it, if not more.
World moves on as India dithers
All this has special relevance to energy production and waste water recycling, the two greatest challenges facing us today. The two are closely related; once we have cheap energy, water recycling from sources like polluted rivers and desalination of sea water becomes technically and economically feasible. In fact, some of the greatest interest in the use of solar power happens to be in the energy rich Middle East, in places like Dubai and Bahrain which get plenty of sunshine but are short of water. So the push is on to exploit cheap solar energy to alleviate water shortage.
By contrast, the Indian government has been at best indifferent in its promotion of solar power and technologies related to it including nano. This was clear during the recently held Global Indian Business Meet (GIBM) in New York which I participated in and spoke on these topics. There was considerable excitement and interest from among the participants but nothing from India. Curiously, several of the leaders in these technologies, even at prestigious institutions are persons of Indian origin. But there was no participation by anyone from the Indian government even though I had personally impressed upon the Planning Commission to have a presence. (An acquaintance there told me that he could not leave Delhi for several weeks because the PM who is also the Chairman could call a meeting any time!)
The Planning Commission has been a dinosaur almost from the time it was born, but Indian science, particularly experimental science which holds the key to these fast emerging fields seems no better. Bangalore has several centers flaunting the title ‘advanced’ that do no experimental work worth the name. These centers (like the Planning Commission) have become post-retirement resorts for elderly scientists and political favorites. Ambitious young scientists are forced to look for opportunities in other countries, especially the U.S., which is always on the lookout for young scientific talent.
Nanotechnology as a field is still very young that calls for young people with energy and fresh minds. The two key scientists at Daniel Nocera’s Sun Catalityx, Dr. Arthur J. Esswein and Dr. Steven Reece are in their early thirties and full of energy. The U.S. National Science Foundation says nano is “at a level of development similar to that of computer technology in the 1950s,” and holds that nano-energy in particular shows tremendous promise. My own sense, based on extensive contacts with key research centers in the U.S. and Europe is that the situation today is closer to computing in the 1960s when semiconductor devices were making their way into computers. But a major breakthrough can upset all calculations.
While the Indian government and academia are at best indifferent, private parties are quite active. It has been the same with solar. For example, those interested in learning more about what is going on in nanotechnology are advised to contact NANO2012 at www.nano2012.org/ for a forthcoming conference. It is being hailed as the “most renowned scientific gathering of distinguished scientists in the field of Nanomaterials.” The event will be in Bangalore in the first week of December. It should certainly be of interest to persons interested in nanotechnology. The world is not going to stand still waiting for India to wake up.