Degussa Aktiengesellschaft

Forschungszentrum Juelich Gmbh

Andreas Fischer

Christian Wandrey

Andreas Bommarius

Ralf Zuber

Guenter Knaup

Hartmut Wendt

Karl-Heinz Drauz

Alexander Schwarz

A porous gas diffusion electrode for membrane fuel cells on an ion-conducting polymer. The electrode contains a finely divided electrocatalyst which is dispersed in a proton-conducting ionomer and has a total porosity of more than 40 to less than 75%. It supplies considerably improved performance data in comparison to known electrodes. The electrode can be produced by using pore-forming materials which are dissolved during the re-protonation of the ion-conducting polymers with sulfuric acid or are decomposed by the action of temperature.

Gas diffusion electrode for membrane fuel cells and method of its

Protected and unprotected di- or oligopeptides are synthesized by reacting an N-terminally protected .alpha.-amino acid alkyl ester or peptide alkyl ester of the formula X--E--R.sup.1 with an amino acid or a di- or oligopeptide or a derivative thereof of the formula H.sub.2 N--Q--R.sup.2 in aqueous solution in the presence of a hydrolase, and, removing protective groups from the reaction product separated from the reaction mixture, where E is the residue of an .alpha.-amino acid or of a di- or oligopeptide, R.sup.1 is lower alkyl and X is a group which carries a charge or is polar at the pH values used for the reaction and which increases the solubility by a factor &gt;5 compared with compounds wherein X=H, Q is the residue of an amino acid or of a di- or oligopeptide, and R.sup.2 is an optionally esterified or amidated acid group. In a preferred embodiment, the peptide or (.alpha.-)amino acid ester concentration is greater than 50 mM, wherein in a particularly preferred embodiment, the concentration ranges from 100 to 1000 mM with approximately comparable nucleophile and electrophile concentrations. The preferred substrate/enzyme ratios are &gt;10.sup.5 M/M or &gt;10.sup.3 M/M when papain is employed. Phthalyl, maleyl or citraconyl radicals and their derivatives or N-betainyl compounds are envisaged for use radicals (X) in the electrophilic component.

Process for the enzymatic preparation of protected and unprotected di-

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Bonn, Germany

Andreas Fischer