A bipolar membrane combines a cation exchange layer and an anion exchange layer in a single film. When voltage is applied in the right direction (reverse bias), water splits into H⁺ and OH⁻ ions at the interface between the layers, so acid and base can be produced without gas evolution. Fumasep FBM is reinforced with woven PEEK, has a dry thickness of 130–160 µm and is supplied as a 100 × 100 mm sheet.

Unlike Nafion (cations only) and FAA-3 (anions only), it carries two opposite layers in one membrane. Orientation matters: the cation exchange side marked "cathode side" must face the cathode; mounting it the wrong way round can cause blistering and delamination. It is delivered wet in NaCl solution, must never dry out and should be used at 40 °C at most.

Key Features

Single-film bipolar membrane with cation and anion exchange layers
Water splitting voltage below 1.2 V at 100 mA/cm², efficiency above 98% (0.5 M NaCl, 25 °C; manufacturer data)
Woven PEEK reinforced; dry thickness 130–160 µm, 0% swelling in water
Produces H⁺ and OH⁻ without gas evolution
The side marked "cathode side" must face the cathode; operated in reverse bias
Delivered wet in NaCl solution; never let it dry, maximum 40 °C

Technical Specifications

Membrane type	Bipolar membrane (cation + anion exchange layer)
Reinforcement	Woven PEEK
Thickness (dry)	130–160 µm
Weight per area (dry)	15–17 mg/cm²
Dimensional swelling in water	0% (25 °C)
Water splitting voltage	< 1.2 V (100 mA/cm², 0.5 M NaCl, 25 °C)
Water splitting efficiency	> 98% (100 mA/cm²)
Maximum operating temperature	40 °C
pH stability	pH 1–14 (25 °C)
Orientation	Cation exchange side ("cathode side") to the cathode, anion exchange side to the anode
Delivery and storage	Wet in NaCl solution; store in 1 M NaCl in a closed container; not stable against chlorine (Cl₂)
Size	100 × 100 mm