▎ 摘　　要

NOVELTY - The filter unit (100) has a filter element (101) which is filled with a filter material (103) which comprises cyclodextrin. The filter material comprises one material from the following list of materials such as alpha-cyclodextrin, beta-cyclodextrin, gamma-cyclodextrin, powdered cyclodextrin, polymeric cyclodextrin, and pressed cyclodextrin. The filter material comprises one material from graphite, graphene, phthalocyanine, silica and ceramic foam. The filter unit comprises one interface for applying a vacuum. A temperature control element is configured for setting a temperature in the filter element. USE - Filter unit e.g. hydrogen tank for filtering fluid for operating fuel cell of fuel system such as solid oxide fuel cell system or membrane fuel cell system, using cyclodextrin (claimed). ADVANTAGE - The operation of fuel cells with pure hydrogen or hydrogen that is essentially free of impurities is achieved. The fluid is optimized for efficient operation of a fuel cell system. The filter unit acts as a pressure reducer, and is configured to reduce a pressure at which the fluid flows onto the fuel cell stack to a predetermined pressure. By cleaning a respective filter material, a cost-effective operation of a fuel cell system can be made possible. By exchanging a respective filter unit, a long maintenance interval can be achieved when operating a fuel cell system. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (1) a fuel cell system; and (2) a method for operating a fuel cell system. DESCRIPTION OF DRAWING(S) - The drawing shows the schematic diagram of the filter unit. Filter unit (100) Filter element (101) Filter material (103) Fluid (105) Impurity (107)