A porous electrode assembly for tissue heating and ablation systems and methods includes a wall having an exterior peripherally surrounding an interior area. The assembly includes a lumen to convey a medium containing ions into the interior area. An element couples the medium within the interior area to a source of electrical energy. According to the invention, the wall includes at least two spaced apart zones. Each zone comprises a porous material sized to pass ions contained in the medium, to thereby enable ionic transport of electrical energy from the source through the medium and porous material to the exterior of the wall. In a preferred embodiment, the at least two zones are spaced apart by a third zone comprising a material that blocks passage of ions contained in the medium.