An improved technique for producing hydrogen by electrolysis
Material improvenments is an essential prerequisite for the use of renewable energy in large scale.
Production of hydrogen by electrolysis of water using renewable energy is expected to become increasingly important in the future. Currently, it is usually more expensive to produce hydrogen from natural gas by reforming rather than by electrolysis. The day produced only 4% of world hydrogen by electrolysis. A significant reduction in the price of hydrogen from electrolysis coupled with rising prices for oil / gas could change this. An essential element here is that the efficiency of the electrolysis process is pretty low and there is great potential for improvement.
Research activity within hydrogen production by electrolysis of water has until now been remarkably small, compared with research activity in fuel cells. This despite the fact that hydrogen produced by renewable energy is a prerequisite for the use of fuel cells could possibly lead to a reduction in the use of fossil fuels. Likewise, water electrolysis is crucial for wind, wave, hydro and solar energy so far also can be used to produce fuels for transport. There is thus an area which is relatively open, both in research and commercially. On the other hand, it is precisely now (from 2007) been heavily upgraded, not least in the EU context, and it is expected that future will be greatly increased focus on the topic.
Technology developed for fuel cell research can also be used for water electrolysis.
An alternative to the dominernde electrolysis technology is to use the technique known from polymerbrændsels cells (PEM), which uses proton conductive polymer membranes as electrolytes. There are basically talking about reversing a fuel cell, ie. impose a voltage so that it "runs backwards" and then develops H2 and O2 from water, instead of burning H2. The principle of PEM fuel cells are described under research project "Fuel Cells". Because of the anodic oxygenudvikling in cells by electrolysis, the Oxygen, however, be more resistant than required by fuel cells and carbon / graphite can not be used. Instead they have so far tried to use titanium, niobium or tantalum. There is thus a number of material problems (high cost) associated with PEM electrolysis technology in its current form, and this has limited its use compared to conventional alkaline electrolysis. On the other hand, can operate at much higher temperatures up to 150 ° C or even 200 ° C. Not least therefore expected to achieve much higher efficiency since a higher operating temperature means that the required energy (ΔG) for operating water decomposition process decreases.
New materials technology must be developed: New surface coatings.
As shown there is a need for new electrode materials, especially at the anode side, which both meet the technical requirements, and simultaneously is sufficiently cheap. There are, of course, in addition, a number of other issues also may be subject to further research and development, not least new cheaper catalysts are not based on precious metals, and new polymer membranes with higher conductivity etc, just as in fuel cells.
For anodes ("Oxygen") may issue till no summed up the need to develop new materials or surface coatings that are chemically sufficiently resistant to water vapor oxygenblandingen, combined with the anodic potential at the anode during water electrolysis. These surfaces must also be sufficiently electrochemically active to the excitement kept suitably low - even through prolonged use.
At the cathode, corrosion problems are less, since the potential is precisely the reduction and metals is not oxidized. In return, this is one important requirement that over voltage for hydrogen development must be kept low, and of course the price is reasonably low.
In our research on electrode materials for water electrolysis here at DTU Kemi, we plan to test various refractory metals (Ta, Nb, Ti, Zr or Mo) only in solid form, then as coatings on copper or steel. These metals may have an additional coating for not passivate, ie. done elektrokatalytiske. This can be achieved by coatings containing platinum group metals or oxides thereof.
Scanning electron microscope image of crystals of niobium on the surface of coating precipitated by salt melt electrolysis
Offered assignments in the manufacture of coatings, electrochemical characterization and test them in electrolytic cells (New electrode materials for hydrogen production by water electrolysis). The work is closely linked to research in fuel cells.
The Institute has had a longstanding collaboration with Danfoss A/S regarding. coatings with refractorymetaller, especially tantalum, which has resulted in the creation of a new device, Danfoss Tantalum Technologies, which continues to operate at the institute.
Beginning in 2007 collaboration with the University of Iceland who is known internationally for their commitment to the introduction of a "hydrogen economy" in Iceland, and with the Physik Department, Technical University of Munich.
For further information contact: Niels J. Bjerrum, Erik Christensen, Jens Oluf Jensen, Jens von Barner or Irina Petrushina
Sidst opdateret af 02.11.2011
Danmark har særlige traditioner indenfor udviklingen af vandelektrolyse. I årene omkring 1900 gennemførtes på Askov Højskole et ”fuldskalaforsøg” med indførelse af et lokalt ”brintsamfund”. Der udførtes en lang rækkende grundlæggende undersøgelser af vindmøllers funktion, og højskolens daværende forstander, Poul La Cour, står som dansk vindmølleindustris fader. Hans idé var imidlertid allerede fra starten i 1891 at oplagre vindeenergien ved elektrolyse af vand til ilt og brint, da akkumulatorer på det tidspunkt var for dyre. Se i øvrigt Poul La Cour museets hjemmeside.
La Cour tog i 1893 kontakt til italieneren Pompeo Garuti, som havde konstrueret et teknisk anvendeligt elektrolyseapparat. Det bestod af en blyforet trækasse, hvor væsken var fortyndet svovlsyre. Elektroderne var også af bly. La Cour skriver selv, at han "opnaaede en Overenskomst, hvorved Danmark skulde have fri Afbenyttelse af det konstruerede Apparat og hvad dermed blev sat i Forbindelse, imod at Selskabet skulde have Retten uden for Danmark ogsaa over, hvad jeg under Vindforsøgene muligvis fandt af hensigtsmæssigt paa dette Omraade."
La Cour udviklede selv videre på systemet, og omkring år 1900 kunne han oplyse: "Nu laves Apparaterne udelukkende af Jærn, og Væsken er en opløsning af kaustisk Natron. Kali kræver en endnu mindre elektrisk Spænding….." Tegningen viser et sådant apparatur. Luftarterne opsamledes i hver sin ”pyramide” med afledning gennem toppen.
Med hensyn til valg af elektrolyt og materialer ligger dette faktisk temmelig tæt på den nuværende ”alkaliske elektrolyse”.
Man arbejdede i princippet med de fleste aspekter af brintsamfundet: Vindkraft, vandelektrolyse, lagring af brint, distribution (Askov Højskole havde rørledninger med hydrogen og oxygen), anvendelse til belysning (der konstrueredes en særlig lampe, der benyttede knaldgas) samt andre anvendelser, bl.a. eksperimenteredes med en brintmotor. Brintdistributionssystemet blev nedlagt ca. 1930, idet energiprisen her generelt blev så lav, at det dengang blev urentabelt.