Progress On Hydrogen Production By Enzymes

Scientists at the Max Planck Institute for Chemical Energy Conversion (MPI CEC) and the Ruhr-Universität Bochum (RUB) have found a hydrogen-producing enzyme activity that efficiently produces hydrogen, which has great potential as a renewable energy source.

Using a spectroscopic investigation the scientists analyzed an enzyme that catalyses the formation and conversion of hydrogen. In the enzyme’s center is a double-iron core, and is therefore also called “FeFe” hydrogenase.  Hydrogenases are of great interest for energy research, since they can efficiently produce hydrogen. However, new catalysts can only be developed given a deep understanding of their mode of action.

The research team describes their results with a paper published in the journal “Angewandte Chemie”.

The Max Plank team has learned electron transfer occurs over several steps.  In hydrogen gas production, H2, two electrons get together with two protons. The research team showed that, as expected, the first electron is initially transferred to the iron center of the enzyme. The second transfer on the other hand is to an iron-sulfur cluster that is located on the periphery, forming a temporary storage for the second electron.

This “super-reduced” state may be responsible for the extremely high efficiency of the hydrogenase. Subsequently both electrons are transferred in one step from the enzyme to the protons, so that hydrogen is generated.

Agnieszka Adamska, a doctoral student at MPI CEC who carried out the spectroscopic studies said, “Only the use of two different spectroscopic techniques made the discovery possible.”

Camilla Lambertz, a postdoc at the RUB who prepared the biological samples for the project looks at the productivity saying, “Up to 10,000 molecules of hydrogen per second can be generated by a single FeFe center.”  Keep in mind that a gram or mole of hydrogen gas or H2 is about 6*10^23 molecules vs 1*10^4 production per enzyme molecule.  The enzyme is thus among the most efficient hydrogenases and is therefore also being intensively investigated by biologists and chemists with a view to achieving environmentally friendly hydrogen production.

The complete mechanism of hydrogen formation is, however, complex and several steps need to be clarified. Next, the researchers at MPI CEC and the RUB aim to use sensitive spectroscopic methods to locate the proton to which the two electrons are transferred. This negatively charged hydrogen atom (hydride) reacts with another proton to form hydrogen. Inspired by the FeFe hydrogenase, the researchers would like to develop their own hydrogen-producing catalysts that could be used for the generation of hydrogen.

Sounds good.  Bur what are the reactants and the energy input requirements?  Usually the German press releases are quite on point and complete.  But here there are basic questions that diminish the news value.

In view of Germany taking the lead in serious concern for carbon dioxide in the atmosphere and a run to the exits from fission nuclear power the need for energy supplies is going to get very costly for a leading economy.  Just how a hydrogen molecule catalyst is going to help remains a puzzle.

One might celebrate with more acclaim if the source and cost of the electrons and protons being used were better explained and understood.  Meanwhile, a hydrogen catalyst could be quite beneficial from simply making H2 fuel on to all the other uses that consume hydrogen.

Our cup is out – More info, Please?

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