A thin film structure, method of producing it and the use thereof. The thin film structure comprises a substrate with a thin conductive layer containing an oxidizing enzyme mixed with an electron transfer mediator. The thin layer is protected against wetting to allow for its storage in dry conditions and further being sufficiently porous to allow for immediate activation of the oxidizing enzyme when contacted with an aqueous solution. The thin film can be used as a cathode in electrochemical fuel cells.
