Did you know that just one-thousandth of the sun’s light that reaches the earth could satisfy all of humanity’s energy nine times over? What if we capture this energy cheaply? Perhaps, artificial leaves are the answer?
Today we have solar cells to make energy. But there are some problems. If it gets cloudy, these cells aren’t much use. Solar cells are also expensive. Also, they do not convert light into electricity very efficiently. But there is a solar cell that’s been around for two billion years that’s perfect. It is the leaf of a plant!
How natural leaves do it
As you know, leaves are the part of a plant where photosynthesis occurs. In this, the leaf uses light energy to convert carbon dioxide & water into glucose.
Photosynthesis has two parts. One part is where hydrogen ions join carbon dioxide to make glucose molecules. The other part is more important to us. This part takes up energy from sunlight and uses that to split water into hydrogen and oxygen. All this happens in a big complex of proteins and chlorophyll.
Scientists have figured a way to make a simple device that works like a leaf. One part of it will capture sunlight, and another part will transfer the energy to a cell which will split water into hydrogen and oxygen, which can be stored in tanks. When we need energy, we can put these gases in a fuel cell, where they react to form water and release electricity.
The trick is to find material that is cheap enough for building millions of such devices. These can then be put in vehicles and power plants. Right now a big search is on for finding materials to do these things.
Finding Cheap Materials
Why not directly use the chlorophyll present in leaves? That’s what a team in North Carolina State University in USA did. They extracted chlorophyll from leaves and trapped it in a transparent jelly(Petrolatum). They put tiny electrodes made of carbon nanotubes in this jelly. When sunlight falls on chlorophyll, it seizes a photon and releases an electron. The electron is carried away by the carbon nanotubes to make electricity.
This electricity can drive a cell in which water is split to form hydrogen and oxygen. For that, another team in Massachusetts Institute of technology, USA have found cheap materials to make a cell. It uses electrodes made of indium and tin oxide, and an electrolyte of cobalt and phosphorus ions. This is able to split water quite efficiently.
If we put these two parts together, we can get a cheap artificial leaf that collects energy from the sun. But it is still sometime to go before we have a small, cheap and portable device that can go into our car. But by the time you’re grown, it might be ready!