New solar cell powers hydrogen economy

25 September 2014
Posted by Chris Smith.

Low-cost production of hydrogen from water using solar energy has been unveiled by Swiss scientists this week.

Hydrogen is regarded as an excellent candidate future fuel on the grounds that it is relatively easy to store and it burns cleanly, yielding just heat and water. But present methods of producing hydrogen usually involve the reaction of methane with steam at high temperature, which is energy intensive and produces carbon dioxide as a bi-product.

As such, any environmental benefit arising through the use of the hydrogen is more than offset by the carbon footprint. Instead scientists would like to produce hydrogen using electricity from renewable sources to split water into hydrogen and oxygen, with soalr power being one obvious choice.

Unfortunately, the present generation of silicon-based cells cannot product a sufficiently high output voltage individually, meaning that several of them need to be linked together in series. Expensive and heavy as they are, this makes them an impractical source for efficient hyodrogen production.

Now, writing in Science, Michael Gratzel and his colleagues at the Swiss Federal Institute of Technology in Lausanne have unveiled a working solar-hydrogen system based on a new type of solar material called a perovskite cell, which is a compound containing lead, nitrogen carbon and iodine.

Critically, these cells generate a much greater potential difference, returning 0.9 volts per cell; just two of them coupled together are capable of splitting water to make hydrogen.

In tests, presented this week in the journal Science, the perovskite cells turned sunlight into electricity with an efficiency of over 17% and drove a hydrogen-generating reaction with an efficiency of 12.3%, the best achieved yet with most rival technologies failing to beat 10%.

And although this may still appear to be low, commentators are remarking that the rate at which perovskite cells are developing, this number may soon top 15%, which is the target set by the US Department of Energy for 2015.

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