Scientists at MIT have demonstrated the first practical artificial leaf.
This doesn’t mean the oak tree out the front of your house should be worried, these leaves will never hang from a branch. Nor do they look like a leaf, with a silicon cell immersed in a cylinder of bubbling water they are more laboratory ready than they are garden ready.
Instead of simply using the solar cell to produce electricity the cells use a special coating on the silicon, along with the power from the cell to split the water into its hydrogen and oxygen components.
Being able to directly convert water and sunlight into storable gas provides solutions to the biggest problems with solar power, no light no power. At night the gas could be fed to a fuel cell to convert the gases back into electricity and water. The holy grail of renewable power just got one step closer.
Based on a silicon solar cell with a special catalyst coated on the surface, professor Daniel Nocera developed the catalyst three years ago. The catalyst and electricity interact to cause the water to split into hydrogen and oxygen ready to be stored. This is Photo catalytic water splitting, the conversion of solar energy into hydrogen via a water splitting process. Various materials are being tested as catalysts, professor Daniel Nocera demonstrated cobalt-nickle but indium tin oxide has also been tested, titanium is being experimented with by other groups. All of them provide a layer to protect the silicon cell – silicon exposed to water breaks down quickly and produces silicon dioxide – and also improve the efficiency of the Photo-catalytic process. By using solar cells no power is required. This is the theory anyway, at the moment a little extra power must be fed to the leaf for it to efficiently produce gas.
Electrolysis has traditionally been the process used to split water into hydrogen and oxygen. At its most basic electricity is passed through water by placing the positive and negatives wires from a power source in the water. At the end of the wires bubbles appear, oxygen on the positive and hydrogen on the negative. Electrolysis is one of those classic school room experiments that many kids get to try. Hook a battery up to two wires in water and watch it bubble away as gas is produced. Which brings us to the other problem with electrolysis, the amount of power it requires to free the hydrogen. Generally more much more energy is required than you will get by back using the hydrogen. Making it more efficient just to do the work with the electric power you started with. The artificial leaf and Photo catalytic water splitting are attempting to improve upon electrolysis, making it more efficient and practical.
Once the gas has been produced by the leaf it is stored and made available to refill you car or provided to a fuel cell to power your house. Hydrogen infrastructure is going to be a huge issue as we try to ween ourselves off oil and this is a very elegant solution to that problem. The petrol station of the future will only require light and water to provide for all of our refueling needs. Home systems are possible by only storing relatively small amounts of the volatile gases. Hydrogen is going to become an essential part of the energy equation for humanity. The most abundant substance in the universe should ensure it never runs out.
The first artificial leaf was developed more than a decade ago by John Turner of the U.S. National Renewable Energy Laboratory in Boulder, Colorado. Although highly efficient at carrying out photosynthesis, Turner’s device was impractical for wider use, as it was composed of rare, expensive metals and was highly unstable — with a lifespan of barely one day. Nocera’s artificial leaf overcomes these problems by being constructed out of common materials and clever manufacturing techniques to increase the lifespan. Normally when water is submerged in water it will produce silicon dioxide, not very useful for power generation. In order to protect the silicon alternative process were developed. In one process a layer of cobalt-nickel was laid down in gas form, this form the catalyst and a protective layer for the silicon.
Ultimately the design will evolve to use the front and back side of the silicon cell. immersing the cell in a cylinder of water divided so that the front would produce oxygen and the back hydrogen. There are still a number of hurdles to overcome yet, solar cells need to become more efficient to be able to self sustain the process. The developers of the artificial leaf hold out hopes that it may supply cheap power to the third world and allow everyone else to change over to a hydrogen economy. Home power and refueling stations with the only emission being water.
Artificial leaves are brilliant idea that’s evolving before our eyes. They are an example of what happens when creative people are inspired by nature, then get busy. With teams working on improving the artificial leaf we can expect some exciting progress in the future. Now if we can develop an electric banana growing tree we’ll all be much happier.
Buddha’s Brother out…
