We heard about hydrogen as a fuel could be easily generated from the solar energy. Sounds amazing! However, there was no convenient or easy solar hydrogen system available in the world from which we can harvest hydrogen from the solar energy directly. The Ideal solar hydrogen system should be such that it creates hydrogen easily from the abundant available material with minimum cost and sufficiently reliable to power cars and homes in future.
I think our search for such kind of system is over; the journal ‘Science’ has published a new way to produce hydrogen fuel from sunlight and water, the method was discovered in Michael Gratzel’s laboratory at Ecole Polytechique Federale Lausanne in Switzerland. Researchers have created a way to use abundantly materials to build a device that uses solar energy and water to make hydrogen. By combining a pair of solar cells made with a mineral called perovskite and low cost electrodes, scientists have obtained 12.3 per cent conversion efficiency from solar energy to hydrogen, a record using earth-abundant materials as opposed to rare materials. The race is on to optimize solar energy’s performance. More efficient silicon photo-voltaic panels, dye-sensitized solar cells, concentrated cells and thermodynamic solar panel all pursue the same goal: to produce a maximum amount of electrons from sunlight.
How hydrogen is made
At the Laboratory of Photonics and Interfaces at EPFL, led by Michael Gratzel, where scientists recently invented dye solar cells that mimic photosynthesis in plants, they have also developed methods for generating fuels through solar water splitting. To do this, they either use photo electrochemical cells that directly split water into hydrogen and oxygen when exposed to sunlight, or they combine electricity-generating cells with and electrolyser that separates the water molecules. By using the latter technique, Gratzel’s student Jingshan Luo and his colleagues were able to convert water into hydrogen using energy diffused by the sun on perovskite absorbers – a compound that can be obtained in the laboratory from common materials, such as those used in conventional car batteries, eliminating the need for rare-earth metals in the production of usable hydrogen fuel.
Store hydrogen in a bottle
This high efficiency provides stiff competition for other tech used to convert solar energy and has several advantages over other methods. “Both the perovskite used in the cells and the nickel and iron catalysts making up the electrodes require resources that are abundant on Earth and that are also cheap,” explained Jingshan Luo. “However, our electrodes work just as well as the expensive platinum based models customarily used.” On the other hand, the conversion of solar energy into hydrogen makes its storage possible, which addresses one of the biggest disadvantages faced by renewable electricity – the requirement to use it at the time it is produced. Once you have hydrogen, you store it in a bottle and you can do with it whatever you want to, whenever you want it. Such a gas can be burned – in a boiler or engine – releasing only water vapour. It can also pass into a fuel cell to generate electricity on demand.
Powerful cells for future
These high efficiency values are based on a characteristic of perovskite cells: their ability to generate an open circuit voltage greater than 1V (silicon cells stop at 0.7V). A voltage of 1.7V or more is required for water electrolysis to occur and to obtain exploitable gases. To get these numbers, three or more silicon cells are needed, whereas just two perovskite cells are enough. As a result, there is more efficiency with respect to the surface of the light absorbers required. This new invention requires more focus on further development to get it more suitable for commercial applications.