A water electrolyzer comprises a membrane, a cathode and an anode. The membrane comprises a first membrane layer comprising a first ion-conductive polymer, a second membrane layer comprising a second ion-conductive polymer, and a platinized nanostructured layer disposed between the first layer and the second layer. The platinized nanostructured layer comprises close-packed whiskers having at least one of platinum or platinum oxide disposed thereon. The cathode is disposed on the membrane and comprises a first catalyst consisting essentially of both metallic Pt and Pt oxide. The anode is disposed on the opposite surface of the membrane and comprises a second catalyst comprising at least 95 percent by weight of collectively metallic Ir and Ir oxide, calculated as elemental Ir, based on the total weight of the second catalyst, wherein at least one of metallic Ir or Ir oxide is present. Membranes and methods of making them are also disclosed.