The present invention relates to microfibrous fuel cell sub-bundle structures, fuel cell bundles and fuel cell assemblies formed by such fuel cell sub-bundles and bundles. Specifically, a fuel cell sub-bundle is provided, which comprises multiple microfibrous fuel cells. Each microfibrous fuel cell comprises: (a) a hollow microfibrous membrane separator comprising an electrolyte medium, (b) an inner electrocatalyst layer in contact with an inner surface of such membrane separator, (c) an outer electrocatalyst layer in contact with an outer surface of such membrane separator, and (d) an individual current collector in electrical contact with the inner surface of such membrane separator. Each of such multiple microfibrous fuel cells is in electrical contact with a common current collector at the outer surface of its membrane separator.