Iron unlocks path to hydrogen fuel.

Nov 21, 2011

Boddien, A, D Mellmann, F Gärtner, R Jackstell, H Junge, PJ Dyson, G Laurenczy, R Ludwig and M Beller. 2011. Efficient dehydrogenation of formic acid using an iron catalyst. Science 333(6050):1733-1736.

Synopsis by Audrey Moores

Researchers look to nature and use iron – instead of precious metals – to transform formic acid into hydrogen for use as a clean source of energy.

For decades, means of producing hydrogen fuel efficiently and without using traditional fossil fuels have eluded chemists and engineers. Yet some organisms sequester the element to fuel their life processes. Their secret lies in iron-based enzymes.

To mimic a hydrogen-based energy source for people, researchers from Germany and Switzerland successfully proved that iron can be a very efficient agent to generate hydrogen from formic acid. The simple and powerful system may have wide commercial appeal if researchers can determine why the system shuts down after just two-thirds of a day. The group's results are published in the journal Science.

Hydrogen is a clean source of energy, with water as the sole combustion waste. Yet it provides a great deal of energy considering its low weight. That explains why it is highly attractive as a future source of clean energy. Much research is currently devoted to designing engines that can run on this fuel.

However, hydrogen is currently produced using energy from fossil fuels, which is a major hurdle to its development as a fuel. It can also be generated by splitting water into oxygen and hydrogen. Again, this reaction requires energy from traditional means, such as fossil fuels, nuclear power or hydroelectric power.

Formic acid is a promising starter material to generate hydrogen, as it is readily available from biomass –  plant or animal material usually collected through agriculture or forestry. Formic acid could also be used to store hydrogen, as it breaks down into hydrogen and carbon dioxide and can be made from these same two molecules. Attempts to harness formic acid have so far fallen short because processing it requires high temperature or additives.  

The big problem is how to easily, efficiently and cleanly break apart formic acid to liberate the needed hydrogen. The researchers – inspired by organisms that do this naturally – found that switching out the precious metal catalysts used now with a simple compound based on iron and phosphorus can transform formic acid into hydrogen and carbon dioxide. No other by-products are produced.

The researchers combined formic acid, the iron-based compound and propylene carbonate, a green and non-toxic solvent. They tested the reaction in a realistic set up where the reaction was constantly fed with formic acid.  

The reaction worked very well at normal temperatures. It was not affected by the presence of common impurities – such as water and air – typically found in formic acid supplies.

Hydrogen production was remarkably stable over 16 hours. After this time, water accumulated and deactivated the system. This difficulty will have to be overcome before the process can be used commercially.

The discovery means that chemists are a step closer to turning formic acid into hydrogen and carbon dioxide. This reaction would ideally happen inside the engine of a car fed with formic acid to allow the generated hydrogen to burn and power the car. The process will generate carbon dioxide, but since formic acid comes from biomass, the whole cycle would be carbon neutral.

This system is preliminary and will need to be elaborated upon and streamlined to meet commercialization requirements. But the system is very simple and powerful and may lead to humans using hydrogen as other organisms already do.

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