Open Session - SWISS GEOSCIENCE MEETINGs

108
Symposium 2: Mineralogy-Petrology-Geochemistry
2.3
Experimental geochemistry and mineralogy for industrial applications:
new membranes for alkaline electrolysers
V. Zakaznova-Herzog*, D. Wiedenmann*, M. Gorbar**, B. Grobéty***, U. Vogt*, A. Züttel*
* Laboratory “Hydrogen & Energy”, EMPA, Überlandstrasse 129, 8600 Dübendorf
Valentina.Herzog@empa.ch
** Laboratory for High Performance Ceramics, EMPA, Überlandstrasse 129, 8600 Dübendorf
*** Dept. of Geosciences, University of Fribourg, Chemin du Musée 6, Pérolles, CH-1700 Fribourg
Mineral stability and reactivity with hydrothermal solutions from low to high temperatures and pressures are important
issues in petrology and geochemistry. These data may also be of importance Industrial applications of such minerals. An
example is the hydrogen production by alkaline electrolysis, for which membranes resisting concentrated KOH solutions are
needed. About 1.6 million tonnes per year of world hydrogen production is by means of electrolysis (U.S. Department of energy,
http://www.hydrogenassociation.org). Currently, chrysotile asbestos membranes are used to separate hydrogen and
oxygen gases during water electrolysis (Fig. 1).
The focus of our project is the study of the currently used asbestos membranes and the development of new membranes to
replace asbestos membranes, which are banned due to recent health regulations. The new material needs to be impermeable
for O 2 and H 2 , ion-conductive, stable in 30% KOH at 90°C and 32 bars, flexible, robust and affordable.. Because of their proven
stability in alkaline solutions and low costs, Mg-silicates, such as olivine (Hänchen et al, 2006), are perfect candidates as replacement
materials. Chrysotile asbestos membranes have a high ion conductance and gas tightness and sufficient flexibility
and mechanical robustness, even for very large dimension i.e. diameters up to 2meters. The reason for these excellent
physico-chemical properties are, however, not well understood.
The electrochemical performance of membranes made of replacement materials will be monitor in a prototype test cell.
Stability and dissolution behaviour of chrysotile asbestos and a selection of replacement materials will be studied before and
after having served in the test cell by means of environmental scanning electron microscopy, X-ray diffraction and X-ray
photoelectron spectroscopy (XPS). XPS is one useful technique for probing chemical states at fresh and reacted surfaces, from
which insight into the stability and the dissolution mechanisms may be gained (e. g., XPS study of fresh and reacted olivine
and pyroxenes, two potential membrane materials, Zakaznova-Herzog et al., 2008). Material solubility will be monitored by
the gravimetrical method and ICP MS.
Fig. 1 Exploded view of a pressure electrolysis unit (Lurgi, Zdansky-Lonza pressure electrolysis): (a Bipolar electrodes, dimple plate cell par-
tition; b) Pre-electrodes in the form of nets c)Asbestos diaphragm; d) Cell frame; e) Hydrogen and oxygen ducts (Häussinger P., et al.,
2006)
REFERENCES
Häussinger P., Lohmüller R., Watson A. (2006) Ullmann’s Encyclopedia of Ind. Chemistry, Chap.: Hydrogen, v.17.
Hänchen, M.; Prigiobbe, V.; Storti, G.; Seward, T. M.; Mazzotti, M.(2006) Dissolution kinetics of fosteritic oli-vine at 90 150 °C
including effects of the presence of CO 2 Geochimica et Cosmochimica Acta, Volume 70, Issue 17, p. 4403-4416
Zakaznova-Herzog V.P., H.W. Nesbitt, G.M. Bancroft and J.S. Tse. (2008) Characterization of Leached Layers on Olivine and
Pyroxenes using High Resolution XPS and Density Functional Calculations Geochim. Cosmochim. Acta 72, 69-86.