How to turn water into rocket fuel – scientists unlock power of the sun

By Steve Connor, Science EditorFriday, 1 August 2008


Scientists have devised a cheap and simple method of turning water into rocket fuel using solar power in a development that could generate a new source of green energy for the home and workplace.
The researchers used electricity from solar panels to split water into oxygen and hydrogen – the constituents of rocket fuel – with a technology that scientists believe could solve many of the problems that have hampered the development of solar energy.
With the help of a simple and yet highly efficient "chemistry set" made out of commonly available materials, the scientists have found a way of storing solar energy as a chemical fuel that can be used to power pollution-free electricity generators known as hydrogen fuel cells.
Until now the concept has stagnated because it has been too costly and difficult to use solar-generated electricity to split water into oxygen and hydrogen in a domestic setting, but the new method relies on the discovery of a catalyst that speeds up the conversion of water into high-energy fuel.
Daniel Nocera of the Massachusetts Institute of Technology in Boston, said the discovery could remove one of the major obstacles that has prevented solar power from being taken up widely as a viable alternative to fossil fuels such as oil and gas.
"The discovery has enormous implications for the large-scale deployment of solar since it puts us on the doorstep of a cheap and easily manufactured storage mechanism. The ease of implementation means that this discovery will have legs," Dr Nocera said.
Being able to use solar panels to build up a store of chemical energy that is easily transported would revolutionise the way solar energy can be used. It not only means that it could power a building at night, it also means it could be carried around to power electric vehicles running on hydrogen fuel cells.
The secret of the breakthrough, published in the journal Science, lies in the type of electrodes used to generate oxygen and hydrogen when they are inserted into water. The scientists made them from a cobalt-phosphate mixture which acted as a catalyst that speeds up the splitting of water molecules into their components – oxygen and hydrogen.
"The simplicity of this process is amazing. Using common and affordable elements, and a glass of water, these chemists may have given us a future way to efficiently obtain oxygen by splitting water," said Luis Echegoyen, director of the chemical division of the US National Science Foundation, which funded the work.
Dr Nocera said that sunlight has the greatest potential of any power source to solve the world's energy problems given that in one hour enough energy from the Sun strikes the Earth to provide the entire planet's energy needs for a year.
The technique of using sunlight to split water lies at the basis of photosynthesis, the way plants convert the energy of sunlight into a chemical store that can be used for growth, but emulating the biological process has not been easy. Existing methods of splitting water using electrolysis are used in industry but are not suited for artificial photosynthesis as they are expensive and cumbersome to use on the sort of small scales needed for homes and offices.
Within a decade, Dr Nocera predicts that people will be powering their homes in the daytime from photovoltaic solar panels, and using the spare energy to generate that hydrogen that will power fuel cells at night with little or no pollution. "This is just the beginning. The scientific community is really going to run with this," Dr Nocera said.
How the new electrodes work
* Sunlight hits the photovoltaic cells of a solar panel and is converted into electricity. Spare capacity is sent to electrodes placed in a tank of water.
* As electricity runs through each electrode, a chemical catalyst made of a cobalt-phosphate mixture lining their surfaces speeds up the rate at which water is split into oxygen and hydrogen.
* The two gases bubble up to the surface and are collected separately and stored in safety canisters. The catalyst covering the electrodes renews itself spontaneously.
* Hydrogen is used as a fuel to drive a generator known as a hydrogen fuel cell, which can power a vehicle or the home at night. Oxygen can be combined with hydrogen to produce energy-rich fuel.
* Scientists are trying to work out exactly how the catalyst works and hope to refine the technique further. They plan to experiment with other catalysts, such as platinum, which is know to speed up the rate at which hydrogen can be made when electrodes are placed in water.
* The system should also be able to work with electricity generated by wind turbines, which also suffer the problem of variable power caused by differences in wind speed. The energy of the wind can be stored for when it is calm.