Barium titanate films grown under a H-2-rich atmosphere display a high dielectric constant and therefore can be employed as electrolytes in the all-solid-state supercapacitors. This behavior was attributed to the accumulation of protons at the metal-electrolyte interface over a Debye length (capacitive double layer). Electrical measurements were carried out on hydrogenated layers (BaTiO3:H) and a trilayer stack (BaTiO3/BaTiO3:H/BaTiO3) to study the active defects at the origin of the conduction mechanisms.