Sometimes referred to as an ionic membrane dehumidifier, Rosahl uses an electrochemical process to continuously transport moisture from inside an enclosure to the outside.

The Solid Polymer Electrolyte (SPE) consists of a proton-conducting polymer membrane with porous electrodes containing a noble metal catalyst. When a 3 V DC supply is applied, water molecules at the dehumidifying (anode) side are split into hydrogen ions (H⁺), oxygen and electrons.

The hydrogen ions migrate through the polymer membrane while the electrons flow through the external electrical circuit. At the moisture discharge (cathode) side, the hydrogen ions, electrons and oxygen from the surrounding air recombine to form water vapour, which is released outside the enclosure.

The overall effect is that moisture is continuously pumped from inside the enclosure to the outside, providing reliable long-term humidity control without compressors, fans or desiccants.

Oxygen is generated at the dehumidifying electrode as part of the electrochemical process. Although this can theoretically result in a small increase in oxygen concentration within a sealed enclosure, the membrane also transports moisture by electro-osmotic drag, so the increase is considerably less than would be predicted from electrolysis alone. In normal applications, any increase remains well below the level regarded as an oxygen-enriched atmosphere and does not present a practical safety concern.

Rosahl has no moving parts, making it silent, vibration-free and economical to operate. Because moisture is transported outside the enclosure rather than stored, the membrane requires no routine maintenance and there are no reservoirs to empty or consumable materials to replace.

The compact, solid-state construction makes Rosahl ideal for remote installations and applications where long service life and high reliability are essential. Typical operating life is measured in years.

By simply reversing the polarity of the DC supply, the membrane can also operate as a humidifier, allowing precise humidity control over a wide range of applications.