Abstract: Disclosed herein are fuel cell elements including at least one electronically conductive layer and an ion conductive layer. The fuel cell elements can have a tubular cross-section or an enclosed cross-section of another shape. Also disclosed is an assembly of fuel cell elements to form cell tubes and stacks of such fuel cell elements or cell tubes. Fuel cell elements, or cell tubes, or stacks thereof can also be used as an electrolyser. Further disclosed are methods of making such fuel cell elements, cell tubes and stacks thereof, as well as methods of using the same.