Abstract: A high surface area valve-metal capacitor electrode is formed on a moving substrate in vacuum by a continuous multilayer vapor-phase deposition process under conditions of substrate temperature and speed that produce continuously growing, uninterrupted dendritic structures. The process is carried out in an atmosphere of inert gas, preferably including He or Ar, with or without an impurity gas such as oxygen. The substrate may be a valve-metal foil or wire, a metal screen, a polymer film, an organic or inorganic fiber, or a composite material. The direction of motion of the moving substrate may be reversed during the deposition process in order to increase the porosity of the dendrites. The electrode may be passivated using an oxygen-containing plasma before exposure to air. The process may also be carried out under conditions that produce boundary-layer turbulence in order to promote the continuously growth of uninterrupted dendritic structures.