TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: The method further comprises: attaching an inner current collector to the hollow fibrous membrane separator at the bore side; attaching an outer current collector to the hollow fibrous membrane separator at the shell side; forming an inner electrocatalyst layer on the hollow fibrous membrane separator at the bore side; forming an outer electrocatalyst layer on the hollow fibrous membrane separator at the shell side.    TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The fibrous substrate structure consists of removable substrate material in solid phase. The fibrous substrate structure comprises an inner current collector, and layer(s) of removable substrate material coating over the inner current collector, so that after the removable substrate material is removed, the membrane-forming material layer coating over the fibrous substrate structure forms the hollow fibrous membrane separator, with the inner current collector at its bore side. The fibrous substrate structure comprises a removal interface (51) in contact with the removable substrate material, which facilitates the removal of the substrate material. The fibrous substrate structure comprises an inner current collector, removable substrate material coating, and an inner electrocatalyst layer coating. The electrolyte medium of the hollow fibrous membrane separator comprises at least one solid electrolyte material.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Materials: The removable substrate material is sublimable materials, meltable materials, or soluble materials. The removable substrate material comprises a soluble material such as acid-soluble materials, alkali-soluble materials, organic-solvent-soluble materials, or water-soluble materials.    TECHNOLOGY FOCUS - POLYMERS - Preferred Materials: The removable substrate material comprises a water-soluble polymeric material is polyvinyl pyrrolidones, polyvinyl alcohols, or polyethylene glycols. The solid electrolyte material comprises an ion-exchange ceramic, or an ion-exchange polymer such as perfluorocarbon-sulfonic-acid-based polymers, polysulfone-based polymers, perfluorocarboxylic-acid-based polymer, styrene-vinyl-benzene-sulfonic- acid-based polymers, or styrene-butadiene-based polymers.